Published papers

Energy efficiency is a key component of movement strategy for many species. In fish, optimal swimming speed (Uopt) is the speed at which the mass-specific energetic cost to move a given distance is minimised. However, additional factors may influence an individual's preferred swimming speed (Upref). Activities requiring consistent sensory inputs, such as food finding, may require slower swimming speeds than Uopt. Further, although the majority of fish display some form of social behaviour, the influence of social interactions on Upref remains unclear. It is unlikely that all fish within a group will have the same Upref, and fish may therefore compromise individual Upref to swim with a conspecific. This study measured the Uopt, Upref and Upref in the presence of a conspecific (Upair) of pile perch, Phanerodon vacca, a non-migratory coastal marine generalist. Uopt was significantly higher than, and was not correlated with, Upref. Fish therefore chose to swim at speeds below their energetic optimum, possibly because slower swimming allows for greater awareness of surroundings. Mean Upair was significantly lower than the Upref of the faster fish in each pair but did not differ significantly from the Upref of the slower fish. Therefore, faster fish appear to slow their speed to remain with a slower conspecific. Our study suggests that environmental factors, including social surroundings, may be more important than energetic efficiency for determining swim speed in P. vacca. Further studies of fish species from various habitats will be necessary to elucidate the environmental and energetic factors underpinning Upref.

N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPD-quinone) is an environmental transformation product of the widely used rubber tire antioxidant, 6PPD. Found in stormwater runoff, 6PPD-quinone has been reported to cause acute lethality at ≤1 μg/L in salmonids like coho salmon, rainbow trout, and brook trout. Conversely, other species such as Arctic char and brown trout are insensitive, even when exposed to significantly greater concentrations (3.8–50 μg/L). Sensitive species exhibit symptoms such as gasping, spiraling, increased ventilation, and loss of equilibrium, suggesting a possible impact on cardiorespiratory physiology. This study investigated sublethal 6PPD-quinone toxicities, focusing on cardiovascular and metabolic effects in two salmonids of varying sensitivity: a sensitive species, rainbow trout (Oncorhynchus mykiss) and a tolerant species, Arctic char (Salvelinus alpinus). Fish were exposed to measured concentrations of 0.59 or 7.15 μg/L 6PPD-quinone, respectively, in respirometry chambers for 48 h to assess temporal changes in resting oxygen consumption compared to unexposed controls. Following exposure, cardiac ultrasound and electrocardiography characterized cardiac function in vivo, while blood gas analysis examined blood composition changes. In both species, changes in resting oxygen consumption were observed. In rainbow trout only, a decrease in end systolic volume and an increase in passive ventricular filling, cardiac output, and PR interval length were observed, indicating cardiac stimulation. Cardiorespiratory symptoms observed following rainbow trout exposure might partly be driven by a significant increase in methemoglobin, resulting in an impaired ability to oxygenate tissues. This study is the first to examine the effects of 6PPD-quinone exposure on the cardiorespiratory system of salmonid fishes and provides information invaluable to a better understanding of the mechanism of 6PPD-quinone toxicity.

Aquatic insects cope with hypoxia and anoxia using a variety of behavioral and physiological responses. Most stoneflies (Plecoptera) occur in highly oxygenated surface waters, but some species live underground in alluvial aquifers containing heterogeneous oxygen concentrations. Aquifer stoneflies appear to be supported by methane-derived food resources, which they may exploit using anoxia-resistant behaviors. We documented dissolved oxygen dynamics and collected stoneflies over five years in floodplain wells of the Flathead River, Montana. Hypoxia regularly occurred in two wells, and nymphs of Paraperla frontalis were collected during hypoxic periods. We measured mass-specific metabolic rates (MSMR) at different oxygen concentrations (12, 8, 6, 4, 2, 0.5 mg/L, and during recovery) for 111 stonefly nymphs to determine whether aquifer and benthic taxa differed in hypoxia tolerance. Metabolic rates of aquifer taxa were similar across oxygen concentrations spanning 12 to 2 mg/L (P>0.437), but rates of benthic taxa dropped significantly with declining oxygen (P<0.0001; 2.9× lower at 2 vs. 12 mg/L). Aquifer taxa tolerated short-term repeated exposure to extreme hypoxia surprisingly well (100% survival), but repeated longer-term (> 12 hours) exposures resulted in lower survival (38-91%) and lower metabolic rates during recovery. Our work suggests that aquifer stoneflies have evolved a remarkable set of behavioral and physiological adaptations that allow them to exploit the unique food resources available in hypoxic zones. These adaptations help explain how large-bodied consumers might thrive in the underground aquifers of diverse and productive river floodplains.

The success and impact of invasive non-native species depend on how they cope with local abiotic conditions, especially in comparison to co-occurring native taxa. In aquatic systems, salinity serves as a key environmental filter, mediating the establishment of invasive species and influencing biotic interactions. However, the mechanistic basis behind these context-dependent responses remains poorly understood. In this study, we examined interspecific differences in metabolic rate, movement behaviour, and their relationship between the worldwide invasive Gambusia holbrooki and a threatened Spanish endemic fish Aphanius iberus across an experimentally-manipulated salinity gradient. Using intermittent-flow respirometry and automated tracking of movement patterns, we compared aerobic metabolic traits and movement behaviours under various salinities. Toothcarp maintained a stable aerobic scope across salinity treatments, whereas invasive mosquitofish exhibited a markedly lower aerobic scope with higher salinity, primarily due to a decline in maximum metabolic rate. This stress response was not linked to increased osmoregulatory costs, as baseline metabolism decreased. Behavioural tests demonstrated consistent species differences in routine locomotion, with mosquitofish showing more exploratory behaviour and toothcarp showing more stop-go behaviour and remaining more stationary overall. Notably, in toothcarps, we found a negative link between standard metabolic rate and space use, suggesting that individuals with higher baseline metabolism may be constrained in their movement. Conversely, in mosquitofish, although salinity affected metabolic capacities, this effect was not reflected in their movement, indicating a weak relationship between metabolism and behaviour, likely supported by trait flexibility. By integrating metabolic traits with behavioural data, our results reveal mechanisms underlying invasive species responses and strengthen predictions of their performance relative to native fishes under changing conditions, such as salinity in inland waters. This highlights the importance of trait-based approaches for predicting responses to abiotic stressors and for evaluating the ecological impacts of invasive taxa.

Triploid Atlantic salmon are sterile and used in aquaculture to prevent escapees from breeding in the wild. Meanwhile, triploids suffer poor animal welfare in the latter marine growth phase. Previous experiments have mainly tested smaller fish, and physiological differences between triploids and diploids tended to be subtle or non-existing. We therefore hypothesized that triploidy first becomes a disadvantage at larger body sizes where scaling constraints become more magnified in triploids owing to them having larger cells with lower surface to volume ratios. We measured metabolic rates, stress responses, hypoxia tolerance, and critical thermal maximum in big (≈3 kg) triploid and diploid Atlantic salmon. Additionally, we assessed gill histology metrics. Big triploids had higher standard metabolic rates, lower aerobic scopes, and reduced tolerances to hypoxia and thermal stress. Oxygen extraction coefficients were overall lower in triploids, suggesting reduced efficiency in gill oxygen uptake. This was further supported by lower lamellar densities which indicate less gill surface area. In conclusion, big triploid Atlantic salmon were more vulnerable to environmental extremes driven by oxygen supply limitation and higher basal maintenance costs. This provides a mechanistic explanation for why triploids become prone to animal welfare issues in the latter growth phase of marine aquaculture.

Objective Cultured catfish are subjected to cold temperatures during winter, as aquaculture ponds are relatively shallow (<1.5 m) and experience seasonal thermal fluctuations. Cold temperatures reduce metabolic processes; however, little is known about comparative differences in metabolic rates, swimming performance, and blood metabolites among principal types of cultured catfish. Therefore, the objective of this study was to address this knowledge gap for catfish types used in the U.S. aquaculture industry. Methods Standard metabolic rate, maximum metabolic rate, metabolic scope, critical swimming speed (Ucrit), and blood metabolites were analyzed at 10°C and 20°C in juvenile Channel Catfish Ictalurus punctatus, Blue Catfish I. furcatus, and hybrid catfish (Channel Catfish × Blue Catfish). Results It was hypothesized that hybrid catfish would have greater metabolic and swimming performance than Channel and Blue catfishes across experimental temperatures due to heterosis. However, metabolic scope and Ucrit did not vary among fish types, but Ucrit was reduced among all fish types at 10°C. Lactate and glucose concentrations were higher and blood pH was lower in fatigued catfish, with Channel Catfish generally differing in blood metabolites from Blue and hybrid catfishes. Conclusions Results indicate that prolonged exposure to cold temperatures limits metabolic processes and swimming capacity, ultimately requiring catfish to allocate energetic resources to maintenance metabolic requirements. Although no distinct comparative advantage was found for any of the catfish types at low temperature, long-term health and survival likely relate to energy stores accrued prior to and during exposure to cold temperatures. These findings provide useful comparative metrics to direct future efforts into investigating the physiological and environmental mechanisms affecting the catfish aquaculture industry.

Hatchery-raised lake sturgeon (Acipenser fulvescens) are essential to the restoration of this species, but deviation from optimal juvenile growth conditions may limit post-stocking survival. This study investigated the effects of temperature for lake sturgeon raised at 15 °C, 18 °C, and 21 °C. Survival, growth, and synthesis and storage of metabolic energy reserves were measured weekly for 6 weeks following the onset of exogenous feeding. No significant differences in survival, total length, body mass, or SGR were observed based on rearing temperature. Whole-body lipid concentrations were stable over 6 weeks of growth, while mass-specific protein concentrations were significantly increased in all treatments starting at week 3, suggesting the prioritization of lean muscle production in early life at all tested temperatures. Furthermore, total protein accounted for a greater proportion of body mass in fish exposed to lower temperatures. Finally, persistent effects of rearing temperature were examined in stocking-size juveniles by measuring standard metabolic rate following acute transfer from 20 °C to each of the initial rearing temperatures. Metabolic rate increased with temperature, with no differences between rearing groups at each of the measured temperatures. However, fish reared at 18 °C demonstrated improved plasticity within the measured temperature range compared to lake sturgeon that experienced low (15 °C) or high (21 °C) temperatures in their early life. These results indicate that temperature plays a role in balancing the trade-off between rapid growth and nutritional condition of juvenile lake sturgeon, and thermal plasticity later in life, which may influence recruitment to depleted populations.

Synopsis Over 97% of ray-finned fish produce free-swimming larvae. With survival rates of less than 0.01% and radically different morphologies from adults, fish larvae play a crucial role in adapting to environmental changes and dispersing fish populations. Despite over a century of research, a critical gap remains in quantifying the energetic strategies of developing fish to determine how species from different thermal environments self-regulate in response to chronic and acute temperature changes and, the energetic costs associated with allostatic adjustments, referred to as allostatic load (RAL). This study examines the metabolic differences in yolk-sac larvae and their capacity to adjust to energetically adjust to chronic and acute temperature change. We studied the yolk-sac stages of two species: (1) zebrafish (Danio rerio, a tropical eurythermal freshwater fish) and (2) Atlantic cod (Gadus morhua, a cold-temperate stenothermal marine fish), under control (C) conditions (28°C for zebrafish and 5°C for Atlantic cod) and compared responses to larvae raised at chronic higher temperatures (31°C for zebrafish and 10°C for Atlantic cod) and exposed to acute temperature change for 1 h in a respirometer (3°C, zebrafish and 5°C, Atlantic cod) during the first week of larval life. Generally, both species exhibited higher metabolic rates and greater energetic-related changes in response to chronic stressors than to acute stressors compared to C conditions. While an acute increase in temperature resulted in some metabolic compensation, acute decrease in temperature led to what appeared to be metabolic dysregulation. Both species demonstrated higher variability in response to acute decreases in temperature compared to other treatments. Overall, the range of metabolic responsiveness was greater in Atlantic cod than in zebrafish, suggesting that stenothermal Atlantic cod have less resilience to changes in temperature than eurythermal zebrafish, at least at the yolk-sac stage and, during the first week of larval life when the yolk limits energy supply.

The inference of metabolic rate from behavioural measurements is an open question in fish biology. Here, we put forward a predictive model of zebrafish ( Danio rerio ) metabolic rate in still water from mouth opening and pectoral‐fin beating. Our analysis revisits experimental results published in this journal, reprocessed to include information about the pectoral‐fin beating. Using Cobb–Douglas function, we identify a positive (negative) correlation between metabolic rate and mouth opening amplitude (pectoral‐fin amplitude), pointing at the interplay between buccal pumping and pectoral‐fin stabilization.

Objective Freshwater systems have undergone major changes relative to their hydrologic profile, thermal regime, habitat, and connectivity due to anthropogenic causes. Migratory species are particularly susceptible to such changes given the distances that they travel and the diversity of habitats occupied through their life history. Because of this, it is becoming increasingly important to understand freshwater species’ behavior and physiology to help facilitate their up- and downstream passage past physical and hydrological barriers. Here, we use a combination of approaches, including an enzyme assay that measures the reduction of oxygen in the mitochondria to evaluate the potential thermal tolerance of juvenile (<1 year old) Paddlefish Polyodon spathula acclimated at three temperatures (12, 20, and 25°C). We also used critical swimming speed trials to determine the swimming capacity and respiration rate of juvenile Paddlefish that were acclimated to those three temperatures. Methods We collected skeletal muscle samples from three areas of each fish (dorsal epaxial white skeletal muscle, abdominal white hypaxial skeletal muscle, and a combination of epaxial and hypaxial skeletal muscle tissue [mix of white and red fibers] from the caudal peduncle) to determine whether the estimated enzymatic thermal tolerance was different across tissue types for potential future application to field-collected adult Paddlefish. Results The temperatures at peak enzymatic activity differed across tissue these collection sites (range: 23.12–35.55°C), suggesting that tissue collection site should be carefully considered. Critical swimming speed did not vary significantly across acclimation temperatures (mean ± SE = 40.4 ± 3.03 at 12°C, 59.18 ± 7.08 at 20°C, and 50.13 ± 11.56 at 25°C). Although respiration rate increased with swimming speed, there were no significant differences in maximum metabolic rate across acclimation temperatures during critical swimming trials. Conclusions These data contribute to filling our knowledge gaps concerning the metabolic demands, swimming behavior, and thermal sensitivity of juvenile Paddlefish and suggest that nonlethal approaches may be possible.

Ocean warming and marine heatwaves are predicted to have adverse impacts on marine organisms. Yet, knowledge of the molecular mechanisms that underpin successful or failed acclimation to increasing temperatures remains incomplete. We conducted an aquaria-based study of early-life stage clownfish comprising of six thermal regimes, measuring the metabolic, and multi-tissue transcriptional response of Amphiprion ocellaris using seven tissues. Sampling at 31°C increased metabolic rates in fish reared at 28°C; however, these effects were reduced with increasing developmental rearing at 31°C. Transcriptomic analysis revealed multi-tissue reprogramming of metabolic processes at +3°C, particularly in the liver-pancreas axis. Importantly, chronic larval-juvenile exposure to +3°C induced the acclimation of metabolic rates and caused the upregulation of oxidative phosphorylation (liver) and the downregulation of insulin secretion (pancreas). These results indicate that temperature increase will drive tissue-wide metabolic reprogramming in fish, with changes in key energetic pathways underpinning fish's ability to acclimate to warming.

Total dissolved gas supersaturation (TDGS), commonly resulting from dam discharge, poses significant threats to fish survival by inducing gas bubble trauma (GBT) in downstream populations. Understanding the sensitivity of fish to TDGS during developmental stages is critical for evaluating survival risks during flood seasons. This study investigated the adverse effects of TDGS on three life stages-eggs, larvae, and juveniles-of the endemic fish Schizothorax prenanti (S. prenanti) in the upper Yangtze River. After hatching in 120 % and 130 % TDG levels, both eggs and larvae exhibited severe GBT symptoms with survival rates declining to 70 % and 77 % respectively, compared to 88 % in the control group. Hatching rates also dropped significantly to 66 % and 59 %, compared to 84 % in the control group. Larvae exhibited a marked reduction in body length at TDG levels above 120 %, while heart rates increased significantly at TDGS levels above 110 %. Juveniles subjected to 120 % and 130 % TDGS showed extensive GBT symptoms, with median lethal times of 92 and 35 h, respectively. After 35 h of exposure, juveniles in the 130 % TDGS group showed significant reductions in active metabolic rate (AMR), standard metabolic rate (SMR), and factorial aerobic scope (F-AS), while critical swimming speed (U crit ) and burst swimming speed (U burst ) remained unchanged compared to the control group. In terms of S. prenanti exposed to 130 % TDGS, U crit and U burst significantly declined when survival rate dropped to 25 %, while AMR, SMR, and F-AS exhibited significant changes prior to mortality occurred. Moreover, AMR, SMR, and F-AS in juveniles were more vulnerable to TDGS than U crit and U burst. These findings enhance the understanding of TDGS-induced stress on developing fish and support the development of ecological management strategies for TDG during flood seasons.

The thermal dependence of metabolism has attracted much attention because metabolism is linked to many ecological properties, from individuals to ecosystems. The rate at which physiological traits change is an important factor to account for when assessing thermal plasticity since the time of exposure might allow organisms to compensate for the effect of temperature on performance. Here, we studied short‐ and long‐term thermal plasticity of metabolic rate and its scaling with body mass of Alpine charr ( Salvelinus umbla ). To do so, we raised juveniles from Lake Geneva at 4.5°C and 8.5°C, measured their routine metabolic rate at their incubation temperature (long exposure, > 6 months), and individuals raised at 4.5°C were also tested at 8.5°C (short exposure, < 24 h). The metabolic rate of Alpine charr increased with temperature, as theoretically expected. We found no effects of duration of exposure on metabolic rate or its scaling with body mass. Despite a long‐term exposure to higher temperature, individuals did not adjust their metabolic rate as compared to individuals exposed to a rapid increase in temperature, questioning the capacity of Alpine charr to compensate for temperature increase through their metabolic rate. Therefore, our data reveal no compensation mechanisms of Alpine charr to counterbalance the acute effect of temperature. Further studies will be required to fully understand the adaptive potential of Alpine charr in the context of global change.

Thermal studies on fish can help us to understand their robustness to warming climates. Most experiments are performed on smaller individuals and may not represent larger life-stages owing to physiological scaling effects, particularly with regards to thermal tolerance and respiratory capacities. In this study, respirometry experiments were performed on big Atlantic salmon (Salmo salar) (≈4 kg) following 3-weeks acclimation to seawater of 9 °C or 19 °C. Additionally, gill and heart morphology traits were assessed. At 9 °C metabolic rates resembled earlier work on smaller fish. However, at 19 °C following stress exposure, 81 % died unexpectedly within ≈6 h while surviving fish struggled to recover a baseline metabolic rate. Most noteworthy was that maximum metabolic rates remained similar across temperature whereas smaller Atlantic salmon previously were found to increase their maximum metabolic rates until near-lethal temperatures. As standard metabolic rates also inevitably increases with temperature, aerobic scopes become reduced at 19 °C. Meanwhile lamellar density was unaffected, indicating similar gill surface areas. However, acclimation to 19 °C reduced ventricle roundness and symmetry, while bulbus width to ventricle width ratios increased. These changes presumably reflect adaptive responses to more metabolically demanding environments. Yet the fish appeared unable to supply sufficient oxygen at 19 °C during stress, which we attribute to physiological scaling constraints. Big Atlantic salmon were therefore more susceptible to stress-induced mortality at elevated temperatures, indicating reduced thermal tolerance relative to smaller individuals. This highlights the need to include larger fish in experiments as the underlying basis for thermal tolerance changes across large differences in body size.

Isogenic (clonal) fish lines are useful experimental models to study effects of environment versus genetics on phenotypic traits, as they can be maintained for generations without change, providing advantages over outbred groups prone to generational change and higher variation. Here we performed experiments on isogenic Atlantic salmon groups that were either heterozygous diploid, homozygous diploid, triploid, or heterozygous diploid incubated at 4 °C instead of 8 °C. We measured metabolic rates, stress response, and hypoxia tolerance to assess whole-animal performance traits. Then we measured the morphology of hearts and otoliths since both are known to be influenced by environmental history. Isogenic, ploidy, and zygosity statuses were confirmed from microsatellite markers. Embryonic development is affected by temperature, hence the 4 °C incubation group was tested 9 months later when it had reached an equivalent size as the other groups. Curiously, a bimodal size distribution emerged in this group. Physiological traits were similar between groups apart from higher standard metabolic rates in the 4 °C incubated fish. Each group had distinct heart morphologies where fish with a slower growth history resembled wild-phenotypes while homozygous fish had the most deviating hearts. Proportions of vaterite deposition in otoliths showed high individual variation and did not differ between groups. Lower coefficients of variation within groups were found when compared to outbred fish, but this was not consistent for all traits assessed. As such, substantial phenotypic variation in physiology and morphology was still observed in isogenic Atlantic salmon, which can be ascribed to random environmental factors.

Objective We investigated whether physical enrichment can be used at the captive-rearing stage to promote a more natural phenotype and better prepare juvenile Lake Sturgeon for the variability of the natural environment upon release. Methods We exposed age-0 Lake Sturgeon to different types of physical enrichment for 6 months. We used four treatments: a nonenriched (control) tank, a tank with gravel substrate, a tank with vertical structures, and a tank with both gravel substrate and vertical structures. We tracked the survivorship, growth, and body condition of each fish throughout the experiment and analyzed their dorsal color pattern prior to and following 5 months of enrichment exposure. At the end of the experiment (6 months), we measured several physiological parameters, including metabolic rate, plasma cortisol, and critical thermal maximum. Results We observed mortalities in all the enriched tanks but not in the nonenriched tank. Growth rate and body condition varied considerably between enrichment treatments across time. The fish that were reared with structures alone displayed a lower routine metabolic rate and higher aerobic scope than those in all the other treatment groups. We did not observe any effects of enrichment on the critical thermal maximum or the baseline or stress-induced cortisol levels in these fish. Conclusions We recommend that hatchery managers add structures that allow for sheltering and resting behaviors to the rearing environment of age-0 Lake Sturgeon for a few months prior to release. Our study highlights the value of physical enrichment for improving the welfare of captive-reared fish, which could translate to higher rates of postrelease survival and success for reintroduced age-0 Lake Sturgeon.

Variation in rates of oxygen uptake (Mo 2 ) among individuals within a species is widespread and observed during both rest and activity. Such variation is expected to be important in animal physiology, ecology, and evolution, yet the mechanistic bases for this variation are incompletely understood. In the present study, we asked whether interindividual variation in Mo 2 at rest (standard Mo 2) and during an incremental swim test (peak swimming Mo 2 [peak Mo 2,swim ]) in Gulf killifish ( Fundulus grandis ) is related to variation in mitochondrial Mo 2 in five tissues: heart, oxidative skeletal muscle, glycolytic skeletal muscle, liver, and brain. After accounting for the effects of body mass, Mo 2,standard was positively related to liver mass and its maximum capacity for oxygen flux by the electron transport system (ETS). Peak Mo 2,swim was positively related to ETS respiration by heart ventricle and mitochondrial respiration required to offset the dissipation of the proton gradient in the absence of ATP synthesis (LEAK) by glycolytic skeletal muscle. The relationship between peak Mo 2,swim and glycolytic muscle LEAK respiration prompted us to examine the relationship between the aerobic cost of transport and mitochondrial phosphorylation efficiency in glycolytic skeletal muscle. We found that individuals with a lower phosphorylation efficiency consumed more oxygen to travel a given distance (i.e., had a higher aerobic cost of transport). This result supports the idea that LEAK respiration represents an energetic cost during activity, which might be partially offset if higher LEAK results in less reactive oxygen species formation.

Skeletal muscle function and quality are strong indicators of metabolic health. Here, we present a protocol for skeletal muscle phenotyping in zebrafish. We describe steps to evaluate spontaneous locomotion, measure oxygen consumption during incremental exercise, and analyze cross-sectional area of skeletal muscle cells in adult zebrafish. This protocol has potential applications to assess zebrafish muscle quality and function in studies of metabolic diseases, aging, and skeletal muscle health. For complete details on the use and execution of this protocol, please refer to Grepper and Tabasso et al. 1.

Di-2-ethylhexyl phthalate (DEHP), a widely used plasticiser, is a pervasive environmental contaminant with potential detrimental effects on aquatic organisms. The objective of this study was to provide an integrative analysis of how DEHP alters energy balance, temporal homeostasis and fish welfare - interrelated aspects critical to animal survival - to address critical gaps in our understanding of its toxicological effects. Goldfish (Carassius auratus) were chronically (14 days) treated with DEHP. Energy balance was assessed through locomotor activity, metabolic rate, feed intake, and growth indices. Daily of locomotor and metabolic rate rhythms were examined to explore potential circadian disruptions. Anxiety-like behaviours were also examined to assess welfare. DEHP decreased feed intake and food-anticipatory activity (FAA), suggesting an anorexigenic effect, which may have been mediated by increased expression of anorexigenic genes in the hypothalamus and liver, along with decreased expression of orexigenic npy (neuropeptide Y) gene in the hypothalamus. Growth parameters remained unchanged, probably due to compensatory reductions in energy expenditure, as indicated by decreased locomotor activity and metabolic rate. Daily rhythms in these two parameters were preserved, suggesting no disruption in temporal homeostasis. DEHP increased hepatic expression of peroxisome proliferator-activated receptor (PPAR)-related genes, suggesting that PPARs activation is a potential mode of action for DEHP in fish. Anxiety levels were elevated, as evidenced by increased thigmotaxis and scototaxis in behavioural tests, which may be mediated by changes in hypothalamic neuropeptides. These findings highlight the adverse effects of DEHP on energy regulation and animal welfare, providing novel insights into its broader physiological consequences in fish.

Temperature fluctuations challenge ectothermic species, particularly tropical fish dependent on external temperatures for physiological regulation. However, the molecular mechanisms through which low-temperature stress impacts immune responses in these species, especially in relation to chromatin accessibility and epigenetic regulation, remain poorly understood. In this study, we investigate chromatin and transcriptional changes in the head kidney and thymus tissues of Nile tilapia (Oreochromis niloticus), a tropical fish of significant economic importance, under cold stress. By analyzing cis-regulatory elements in open chromatin regions and their associated transcription factors (TFs), we construct a comprehensive transcriptional regulatory network (TRN) governing immune responses, including DNA damage-induced apoptosis. Our analysis identifies 119 TFs within the TRN, with Stat1 emerging as a central hub exhibiting distinct binding dynamics under cold stress, as revealed by footprint analysis. Overexpression of Stat1 in immune cells leads to apoptosis and increases the expression of apoptosis-related genes, many of which contain Stat1-binding sites in their regulatory regions, emphasizing its critical role in immune cell survival during cold stress. These results provide insights into the transcriptional and epigenetic regulation of immune responses to cold stress in tilapia and highlight Stat1 as a promising target for enhancing cold tolerance in tropical fish species.

The importance of energy budgets in understanding the ecology, conservation and production of crayfishes has long been recognized. Standard metabolic rate (SMR) estimates the minimum metabolic rate required for basic maintenance of an organism while at rest, and is a critical parameter for investigating energy balance and metabolism. Estimating SMR involves quantifying oxygen uptake under specific conditions. Standard methodology for estimating SMR has been described and evaluated for fishes, but not thoroughly investigated for crayfishes. We adapted a recommended protocol developed for fishes in order to determine appropriate methodologies for measuring SMR in crayfishes. Study animals consisted of 18 individuals of Procambarus clarkii (Girard, 1852) collected in Alabama, USA. Respiration rates were measured using an optical respirometry system (Loligo Systems®; Viborg, Denmark) and intermittent respirometry techniques. Crayfish respiration stabilized the morning after initiation of the trial indicating that a 12 h overnight period was sufficient to acclimate crayfish to respirometry chambers. After 12 h of daylight, respiration of acclimated crayfish typically exhibited a short spike when lights were turned off, indicating data collected within ~2 h following a light change should be excluded from the dataset used to calculate SMR. When calculating SMR, a quantile approach was typically more appropriate than the mean of the lowest normal distribution approach. SMR calculated during the day was only marginally higher than SMR calculated during the night, indicating that SMR can be estimated during either period if shelters are provided in the respiration chambers. Due to the wide diversity of crayfish species and ranges, our recommendations may not be appropriate for every crayfish species or subpopulation. The recommendations can serve, however, as a valuable starting point and the described methodology provides a standardized approach for determining appropriate protocols to measure SMR of crayfish species of interest.

Little is known about the non-thermal climate change factors (hypoxia and acidification) in the context of freshwater invasions. It is supposed that invasive Ponto-Caspian gobies have relatively wide environmental tolerance ranges due to their evolution in the highly variable environment of local limans and estuaries. Thus, we assumed that they better tolerate reduced oxygen and pH levels in invaded areas of Central and Western Europe compared to native species. Using a laboratory respirometry assay, we compared the effect of short-term progressive hypoxia and acidification on routine metabolic rate (RMR) of the invasive racer goby Babka gymnotrachelus and monkey goby Neogobius fluviatilis and their native counterparts sharing similar ecological niches (European bullhead Cottus gobio and gudgeon Gobio gobio, respectively). The natives displayed a lower hypoxia tolerance compared to the gobies (as changes in their RMR appeared at higher oxygen concentrations), whereas the monkey goby, but not the racer goby, appeared more tolerant to reduced pH than its native competitor. Thus, hypoxia tolerance seems to be a key feature shaping the invasive potential of the monkey and racer goby in benthic fish communities. However, the invasion success of the racer goby may be attenuated by progressing water acidification.

The degree of tolerance to adverse conditions ultimately shapes a species' vulnerability to environmental changes. Some studies have reported limited thermal tolerance due to hypoxia in fish employing aquatic respiration. However, there is a lack of information regarding the effects of hypoxia on thermal tolerance in fish exhibiting bimodal respiration. A set of Amazonian fish species has adaptations to breathe air when oxygen in water is not enough to fulfil demand. Additionally, loricariid species within this group possess stomach adaptations for air breathing. The Loricariidae family exhibits varying stomach types and observed morphological differences could influence their ability to obtain oxygen from the air. This ability may, in turn, have consequences for the thermal tolerance of these species. Our objective was to assess the effects of hypoxia on thermal tolerance, along with the physiological (whole-animal metabolic rates and mitochondrial respiration) and behavioural mechanisms involved, in two facultative air-breathing species: Pterygoplichthys pardalis and Ancistrus dolichopterus. These species showcase morphological distinctions in their stomachs, with the former having a higher capacity to obtain oxygen from the air. Thermal tolerance in P. pardalis remained unaffected by dissolved oxygen in the water when air access was available but decreased when access to the water surface was restricted, specifically in hypoxic conditions. Conversely, the thermal tolerance of A. dolichopterus decreased below the critical oxygen partial pressure (Pcrit), even with access to air, highlighting their limited ability to obtain oxygen through their adapted stomach. Our results underscore that air breathing enhances thermal tolerance, but this effect is prominent only in species with a higher capacity for air breathing.

Cardiac taurine efflux is necessary to counteract swelling and protect function following osmotic stress caused by increased cardiac demands and the accumulation of anaerobic end products at high temperatures in fish.

Anthropogenic noise pollution is increasingly acknowledged as a major threat to marine ecosystems, especially for sound-sensitive species, such as the large yellow croaker (Larimichthys crocea). While the effects of underwater noise on fish behavior and physiology have been well-documented, its influence on oxygen metabolism across varying temperatures remains poorly understood. This study examines the impact of boat noise on the oxygen consumption rate (OCR) of juvenile large yellow croakers at different temperatures, a key factor in their metabolic activity. The underwater noise generated by a fishing boat spans a broad frequency range, with a peak spectrum level of 130 dB re 1 µPa at low frequencies between 100 and 200 Hz. Our findings reveal that boat noise significantly elevates the OCR of juvenile fish, with mass-specific OCR increasing by 65.0%, 35.3%, and 28.9% at 18 °C, 25 °C, and 30 °C, respectively. Similarly, individual OCR rose by 60.7%, 35.3%, and 17.1% at these temperatures. These results demonstrate that boat noise triggers a stress response in fish, resulting in heightened metabolic demands across different seasonal conditions. Notably, the impact of boat noise on respiratory metabolism is most significant at lower temperatures. In aquatic environments with stable oxygen levels, the noise-induced rise in oxygen consumption could lead to hypoxia and provoke maladaptive behavioral changes in fish.

Early rearing environment affects performance later in life. In Atlantic salmon (Salmo salar) aquaculture intensive smolt production has been linked to deviating cardiac morphology and increased mortality risks following stressful events during the marine production phase. To investigate the effects of early growth environment on later life-stages, two smolt groups were produced; a fast-growing group reared at 13 °C under continuous light and a slow-growing group reared at 6 °C under a natural photoperiod. The two groups were smoltified and transferred to 9 °C seawater at the same time and at similar sizes, although the slow smolts were ≈ 1000 day degrees older. Respirometry and swim tunnel experiments were performed to assess physiological performances along with morphological analyses of the hearts. We hypothesized that the slower growth trajectory would allow for the development of heart morphology more resembling that of wild salmon and that this should translate into improved physiological performance. Fast-growing smolt had more misaligned and enlarged bulbi as well as asymmetric ventricles compared to slow-growing smolt. However, contrary to our hypothesis, we did not find clear evidence for impaired physiological performance in fast-growing fish. That is, neither standard nor maximum metabolic rates, absolute critical swimming speed, stress recovery, or haematological parameters at fatigue differed between treatments. Mortality risks associated with deviating cardiac morphology first tend to occur in larger sized fish than investigated here. We therefore conclude that while early rearing environment clearly modulates cardiac morphology, recently seawater adapted Atlantic salmon do not yet show signs of compromised functionality associated with cardiac morphological differences at the whole-animal level. Future research should aim to incorporate larger sized fish in physiological experiments for a more appropriate representation of the latter production phase in Atlantic salmon aquaculture and its associated fish welfare problems.

We use the sentinel mangrove crab, Minuca rapax, as a model to investigate the effects of metallic settleable particulate matter (SePM) on wetland. Multiple levels of energetic responses, including (i) metabolic rate and energy budget, (ii) oxidative stress, and (iii) behavioral response by righting time, were assessed as well as the metal and metalloid content in crabs exposed to 0, 0.1 and 1 g.L -1 of SePM, under emerged and submerged conditions over five days, simulating the rigors of the intertidal habitat. Al, Fe, Mn, Cr, and Y exhibited a concentration-dependent increase. Metal concentrations were higher in submerged crabs due to the continuous ingestion of SePM and direct exposure through gills. Exposure concentration up to 1 g.L -1 decreased metabolic rate and enzymatic activities, reduced assimilation efficiency and energy for maintenance, and induces a slower response to righting time, probably by metal effects on nervous system and energy deficits. In conclusion, SePM exposure affects the redox status and physiology of M. rapax depending on he submersion regime and SePM concentration. The disruption to the energy budget and the lethargic behavior in M. rapax exposed to SePM implies potential ecological alterations in the mangrove ecosystem with unknown consequences for the local population.

Digestion can make up a substantial proportion of animal energy budgets, yet our understanding of how it varies with sex, body mass and ration size is limited. A warming climate may have consequences for animal growth and feeding dynamics that will differentially impact individuals in their ability to efficiently acquire and assimilate meals. Many species, such as walleye (Sander vitreus), exhibit sexual size dimorphism (SSD), whereby one sex is larger than the other, suggesting sex differences in energy acquisition and/or expenditure. Here, we present the first thorough estimates of specific dynamic action (SDA) in adult walleye using intermittent-flow respirometry. We fed male (n=14) and female (n=9) walleye two ration sizes, 2% and 4% of individual body mass, over a range of temperatures from 2 to 20°C. SDA was shorter in duration and reached higher peak rates of oxygen consumption with increasing temperature. Peak SDA increased with ration size and decreased with body mass. The proportion of digestible energy lost to SDA (i.e. the SDA coefficient) was consistent at 6% and was unrelated to temperature, body mass, sex or ration size. Our findings suggest that sex has a negligible role in shaping SDA, nor is SDA a contributor to SSD for this species. Standard and maximum metabolic rates were similar between sexes but maximum metabolic rate decreased drastically with body mass. Large fish, which are important for population growth because of reproductive hyperallometry, may therefore face a bioenergetic disadvantage and struggle most to perform optimally in future, warmer waters.

Stress strongly influences the physiology and behavior of animals, and leads into a pathological condition and disease. NMDA receptors (NMDARs) play a crucial role in the modulation of neural activity. To understand the role of NMDARs in fish stress response, we used NMDARs agonist aspartate to test the functional role of its input on the Dahlgren cell population in the caudal neurosecretory system (CNSS) of the olive flounder. In addition, the effect of the NMDARs antagonist D‐AP5 on the expression of genes of the main secretory products of the CNSS after stress was investigated by using qPCR technology and the effect of the NMDARs antagonist D‐AP5 on post‐stress behavior was explored by behavioral methods. Ex vivo electrophysiological experiments showed that the NMDARs agonist aspartate enhanced the firing frequency of Dahlgren cells. Additionally, aspartate treatment increased the incidence of cells exhibiting bursting firing pattern, this result is corroborated by the observed upregulation in the expression of ion channels and major hormone genes in the CNSS. Furthermore, the excitatory influence of aspartate was effectively counteracted by NMDARs antagonist D‐AP5. Interestingly, NMDARs antagonist D‐AP5 treatment also significantly decreased the plasma cortisol levels and the expression of CRH, UI, and UII in CNSS after acute stress. Treatment with D‐AP5 effectively attenuated the stress response, as evidenced by alterations in respiratory metabolism, sand‐burying behavior, swimming distance, simulated capture, and escape response. In conclusion, modulation of Dahlgren cell excitability in the CNSS by NMDARs contributes to the regulation of the stress response, NMDARs antagonist D‐AP5 can effectively suppress stress response in flounder by regulating the stress hormone expression and secretion. Clinical Trial Registration Project code SHOU‐DW‐2022‐032.

In connection with the expansion of alien gobies in European waters, a question arises whether this process can be enhanced or inhibited by global warming. The gobies are of Ponto‐Caspian origin, where the climate is warmer than in invaded European areas. Therefore, they are likely to cope physiologically with climate warming better than native species. Our aim was to identify differences in metabolic traits under elevated summer temperature between the invasive gobies and their native counterparts. Using a laboratory respirometer, we compared the effect of elevated summer temperature (25 vs. 17°C) on the metabolic responses of fish in two species pairs consisting of an invasive goby versus its native counterpart from the same ecological guild: the invasive racer goby Babka gymnotrachelus versus native European bullhead Cottus gobio, and the invasive monkey goby Neogobius fluviatilis versus native gudgeon Gobio gobio. The paired species share functional traits, including morphological characteristics, despite belonging to different fish families. After 4 weeks of acclimation, standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS = MMR–SMR) of the fish were determined. We found that SMR increased under elevated temperature irrespective of species, yet it was always lower in the gobies than in natives. The MMR of the racer goby was lower than that of the bullhead across all temperatures, whereas no differences in MMR were found between the gudgeon and monkey goby. On the one hand, the elevated temperature did not affect the AS of the racer goby and bullhead. However, the AS of the racer goby was consistently lower than that of the bullhead across all temperatures. On the other, elevated temperature caused a decrease in AS in both the monkey goby and gudgeon. However, this temperature‐induced change in AS was higher in the gudgeon than in the monkey goby. In terms of AS, the invaders did not always outperform the natives at higher temperatures. However, the invaders had lower living costs by maintaining a lower SMR. These results suggest that invasion by gobies may be facilitated by global warming, which is likely to increase their occurrence and effect on local fish communities in freshwater temperate systems.

Growing impacts of climate change necessitate predicting species’ vulnerability to altered ecosystems. Assessing vulnerability requires understanding how species’ physiology, life history, and ecology vary among populations and can be altered by behavioral, plastic, and evolutionary adaptations. To examine intraspecific variation in sensitivity to climate change, we measured metabolic responses to acute and chronic temperature exposures in three rearing pond populations of walleye ( Sander vitreus), a cool-water-adapted fish species threatened by climate change. We show significant differences among rearing pond populations in response to increasing temperatures which may originate from broodstock, developmental plasticity, and acclimation. Our results indicate northern walleye may be more tolerant of acute and chronic exposure to higher temperatures by being able to maintain a higher aerobic scope than more southern populations. Furthermore, even over small geographic distances, populations can have significantly different physiological responses to environmental stressors. Quantifying variation in population-specific metabolic responses can inform predictions of growth, reproduction, and fitness across a species range and clarify the importance of within-species diversity in determining vulnerability to environmental stressors.

We recently showed that Crh‐Crhr1 signalling is essential for acute stress‐related locomotor activity in zebrafish larvae. However, the possibility that Crhr1 activation may also initiate the acute metabolic demands for stress coping was unexplored. Here, we tested the hypothesis that Crhr1 signalling is essential for the thermal stressor‐induced increases in the acute metabolic rate, a key response for coping with the enhanced energy demands during stress. We tested this by using a wildtype (WT) and a ubiquitous Crhr1 knockout (crhr1 −/− ) zebrafish and subjecting them to an acute thermal stressor (TS: +5°C above ambient for 60 min). The TS induced the heat shock proteins response in both genotypes, but the elevated cortisol response observed in the WT was absent in the crhr1 −/− mutant. The TS also increased the locomotor activity and the metabolic rate in the WT fish, but this response was inhibited in the crhr1 −/− mutants. To test if this was due to a lack of TS‐induced cortisol elevation in the crhr1 −/− mutant, we mimicked the response in the WT fish by treating them with metyrapone, an 11β‐hydroxylase inhibitor. While metyrapone inhibited the TS‐induced cortisol elevation in the WT, it did not affect the metabolic rate. The lack of Crhr1 also reduced the swimming performance, and the lower U crit in the mutants corresponded with alterations in muscle energy metabolism. Together, our results indicate that Crh‐Crhr1 signalling, independent of downstream cortisol action, is essential for the TS‐induced acute hyperlocomotor activity and the associated increases in the metabolic demand for stress coping.

Pathogens play a key role in individual function and the dynamics of wild populations, but the link between pathogens and individual performance has rarely been investigated in the wild. Migrating salmonids offer an ideal study system to investigate how infection with pathogens affects performance given that climate change and fish farming portend increasing prevalence of pathogens in wild populations. To test for effects of pathogen burden on the performance of a migrating salmonid, we paired data from individual brown trout tagged with acoustic accelerometer transmitters and gill biopsies to investigate how pathogen infection affected whole animal activity during the spawning migration. Generalised additive models fitted to the acceleration data revealed individual and temporal variation in acceleration as expected, but also provided a significant effect of relative infection burden on acceleration. However, when linking this pathogen‐specific effect to a relevant bioenergetic change, it was evident that the effect had little impact on the exercise‐related oxygen consumption at the individual level, especially in cases where fish were not exerting high exercise activity. The results are a powerful example of how pairing non‐lethal biopsies with individual tracking technologies can be used to assess how pathogens impact fish in situ.

Understanding how interactive environmental challenges affect marine species is critical to long‐term ecological and economic stability under global change. Marine calcifiers are thought to be vulnerable to ocean acidification (OA; elevated p CO 2 ); active dissolution of aragonite (Ω ar ) is associated with disrupted development, survivorship, and gene expression in bivalve larvae, resulting in an early life‐stage bottleneck. Dynamic carbonate chemistry in coastal systems emphasizes the importance of multiple stressors, e.g., warming and low salinity events may change organismal responses relative to OA alone. We exposed Eastern oyster larvae ( Crassostrea virginica ) to a full‐factorial experimental design using two temperatures (23°C and 27°C), salinities (17 and 27), and p CO 2 levels (~700 μatm and 1850 μatm p CO 2 ), resulting in Ω ar conditions 0.3–1.7. Ω ar reduced by low salinity, elevated p CO 2, and low temperature, each slowed early development and reduced survival. Low salinity × elevated p CO 2 was linked to severe Ω ar undersaturation (< 0.5) that suppressed expression of bicarbonate transport, biomineralization and augmented expression for ciliary locomotion, proteostasis, and histone modifiers. In isolation and under moderate Ω ar intensity (0.5 < Ω ar < 1), larvae increased transcription for osmoregulatory activity and endocytosis under low salinity, and suppressed transcription for iron metabolism under elevated p CO 2. Although shell growth and survival were affected by Ω ar undersaturation, gene expression patterns of D‐stage oyster larvae and oyster juveniles suggests tolerance to dynamic estuarine environments. Genes and expression patterns that confer survival of postmetamorphosed oysters can improve our understanding of environmental‐organismal interactions and improve breeding programs enabling sustainable production.

The primary function of spermatozoa is to fertilize the oocyte, which depends on their motility and is directly associated with their metabolic state. The oxygen consumption rate (OCR) of spermatozoa reflects the respiratory capacity of sperm mitochondria under various physiological conditions and is an essential marker of sperm quality. We determined the OCR of common carp (Cyprinus carpio) sperm using two respirometry methods: the conventionally used polarographic method with a Clark-type electrode and fluorometric assay with an Oxo Dish optochemical oxygen sensor. The latter was used for the first time to evaluate spermatozoa oxygen consumption in various metabolic states (under different treatments) at different dilution rates. These two methods were compared using Bland–Altman analysis, and the applicability of the optochemical oxygen sensor for evaluating carp sperm oxygen consumption was discussed. Sperm motility and progressive velocity parameters were also assessed to evaluate the effect of sperm respiration under different metabolic states and dilution rates and preincubation period on the physiological status of spermatozoa. The comparison of these respirometry methods clearly shows that while the polarographic method allows immediate measurement of oxygen levels after adding a sperm sample, the optochemical oxygen sensor has a priority in the amount of data obtained due to simultaneous measurements of several samples (e.g., different males, different fish species, repetitions of the same sample or various experimental conditions), even at a later time after adding sperm to the measuring chamber. However, the compared methods are complementary, and the proposed methodology can be applied to other fish species.

To assess the relationship among various measures of thermal tolerance and performance suggested for use in fish, we determined the critical thermal maximum (CTmax), critical swimming speed (Ucrit), maximum thermal tolerance while swimming [CTSmax] and realistic aerobic scope (ASR) of juvenile schoolmaster snapper (Lutjanus apodus). Their CTSmax (37.5±0.1°C) was only slightly lower than their CTmax (38.9±0.1°C) and this is probably because their maximum metabolic rate (MMR) and ASR during the former test were ∼42 and 65% higher, respectively. Furthermore, we did not observe a transition to unsteady (i.e. anaerobically fueled) swimming in the CTSmax test as we did in the Ucrit protocol. These data strongly suggest that thermal tolerance tests on fishes whose lifestyle involves schooling or sustained activity should be performed at ecologically relevant swimming speeds. Our results do not support the hypothesis that failure during a CTSmax test is due to a fish's inability to meet its tissue oxygen demands.

Captive breeding and stocking are commonly employed strategies for enhancing fisheries and conserving endangered fish species. However, hatchery-raised fish often exhibit reduced performance in the wild, displaying alterations in physiological, morphological, and behavioral traits. We tested for differences in swimming capacity and metabolic traits between wild and hatchery-reared individuals of the Spanish toothcarp (Aphanius iberus) from 2 different populations. Furthermore, we experimentally tested if these changes translated into fitness differences after their stocking into the wild. There were significant differences in swimming capacity and metabolic traits between wild and hatchery-reared individuals and also between the 2 populations. Captive-bred individuals displayed consistently lower metabolic rates than wild individuals from the same population (30–76% lower). Critical swimming speed rather differed between the 2 populations. Sex-specific differences were observed in maximum and standard metabolic rates, with wild individuals and females generally exhibiting higher values but with some exceptions. During a 3-month experiment, survival rates did not significantly differ between wild and captive-bred fish. Captive-bred individuals started smaller but exhibited rapid growth during the experiment. Initially, larger captive-bred fish had lower body conditions than their wild counterparts, but these differences progressively diminished. In summary, captive-bred individuals of this fish species showed lower metabolic rates, although the differences with wild individuals slightly depended on sex and size.

Declining body size in fishes and other aquatic ectotherms associated with anthropogenic climate warming has significant implications for future fisheries yields, stock assessments and aquatic ecosystem stability. One proposed mechanism seeking to explain such body-size reductions, known as the gill oxygen limitation (GOL) hypothesis, has recently been used to model future impacts of climate warming on fisheries but has not been robustly empirically tested. We used brook trout (Salvelinus fontinalis), a fast-growing, cold-water salmonid species of broad economic, conservation and ecological value, to examine the GOL hypothesis in a long-term experiment quantifying effects of temperature on growth, resting metabolic rate (RMR), maximum metabolic rate (MMR) and gill surface area (GSA). Despite significantly reduced growth and body size at an elevated temperature, allometric slopes of GSA were not significantly different than 1.0 and were above those for RMR and MMR at both temperature treatments (15°C and 20°C), contrary to GOL expectations. We also found that the effect of temperature on RMR was time-dependent, contradicting the prediction that heightened temperatures increase metabolic rates and reinforcing the importance of longer-term exposures (e.g. >6 months) to fully understand the influence of acclimation on temperature–metabolic rate relationships. Our results indicate that although oxygen limitation may be important in some aspects of temperature–body size relationships and constraints on metabolic supply may contribute to reduced growth in some cases, it is unlikely that GOL is a universal mechanism explaining temperature–body size relationships in aquatic ectotherms. We suggest future research focus on alternative mechanisms underlying temperature–body size relationships, and that projections of climate change impacts on fisheries yields using models based on GOL assumptions be interpreted with caution.

An important goal of environmental and comparative physiology research is to identify species or populations that may be susceptible to environmental change such as heat wave events that are predicted to become more frequent and intense in the future. This study tested the hypothesis that fishes inhabiting alkaline lakes face significant physiological challenges, which results in reduced thermal tolerance. Brook stickleback (Culaea inconstans) were collected from an alkaline lake (pH 9.3) in Alberta, Canada and held under neutral conditions in the laboratory. Subsequently, fish were acutely exposed (4 d) to neutral (pH 7) or alkaline (pH 9.5) waters at 10 or 25°C. Exposure to alkaline water reduced critical thermal maximum (CTmax) in stickleback by approximately 1°C, but thermal acclimation capacity (“thermal plasticity”) was unaffected by alkaline exposure. Alkaline conditions resulted in physiological disturbances characteristic of exposure to high pH including elevated whole-body ammonia and lactate concentrations. Acute warming to CTmax in alkaline-exposed fish resulted in reductions in whole-body sodium and chloride concentrations. In addition, alkaline exposure compromised recovery from exercise at elevated temperatures. Overall, these results suggest that the physiological disturbances observed in response to alkaline exposure may render fish more susceptible to acute warming, reducing thermal tolerance.

Respiratory plasticity is a beneficial response to chronic hypoxia in fish. Red drum, a teleost that commonly experiences hypoxia in the Gulf of Mexico, have shown respiratory plasticity following sublethal hypoxia exposure as juveniles, but implications of hypoxia exposure during development are unknown. We exposed red drum embryos to hypoxia (40% air saturation) or normoxia (100% air saturation) for 3 days post fertilization (dpf). This time frame encompasses hatch and exogenous feeding. At 3 dpf, there was no difference in survival or changes in size. After the 3-day hypoxia exposure, all larvae were moved and reared in common normoxic conditions. Fish were reared for ∼3 months and effects of the developmental hypoxia exposure on swim performance and whole-animal aerobic metabolism were measured. We used a cross design wherein fish from normoxia (N=24) were exercised in swim tunnels in both hypoxia (40%, n=12) and normoxia (100%, n=12) conditions, and likewise for hypoxia-exposed fish (n=10 in each group). Oxygen consumption, critical swim speed (Ucrit), critical oxygen threshold (Pcrit) and mitochondrial respiration were measured. Hypoxia-exposed fish had higher aerobic scope, maximum metabolic rate, and higher liver mitochondrial efficiency relative to control fish in normoxia. Interestingly, hypoxia-exposed fish showed increased hypoxia sensitivity (higher Pcrit) and recruited burst swimming at lower swim speeds relative to control fish. These data provide evidence that early hypoxia exposure leads to a complex response in later life.

Giant clams obtain their nutrition from both filter-feeding and photosynthates produced by symbiotic zooxanthellae within their mantle tissue. The symbiotic partnerships between giant clam and zooxanthellae are critical for the health and survival of giant clams. Therefore, light/dark alternation plays a crucial role in influencing the growth performance and physiological change of the giant clam-zooxanthellae symbiosis in natural ecosystems. In this study, the rhythms of mantle surface area, physiological metabolic activity, and oxidative stress in the boring giant clam, Tridacna crocea, caused by two different light-dark cycles (7:00–19:00 light-on and 9:00–21:00 light-on, respectively) were investigated. The relative mantle surface area, net calcification rate and gross primary production significantly increased with the increase in light time, and the highest values were observed after 4–7 h of light exposure. The values of symbiosis Y (II) sharply increased when giant clams were transferred from dark to light conditions, and then slightly decreased to a low level until the next light/dark cycle. Dynamic changes of zooxanthellae density in the outer mantle were observed with two-peak values noted at 4 h after light-on and -off, respectively. The absorption of ammonium-nitrogen (negative values of ammonia metabolic rate) was observed when giant clams were exposed to light, and the rate reached its highest value after 10 h of light exposure. Rhythmic changes of oxidative stress related enzymes and antioxidant molecule were also detected in the inner and outer mantles. In detail, the highest values of SOD activity were observed around light-on time in both the inner and outer mantles, while the tendency of CAT activity was not the same in the inner and outer mantles; the GSH contents in the inner mantle were significantly higher than that in the outer mantle, and their values significantly increased with light exposure; the MDA concentrations from 5:00 to 14:00 were almost the same in both the inner and outer mantles, which were significantly higher than those at other sampling points. The rhythms of these detected behaviors and physiological responses were almost delayed with the delay of photocycle. This provides experimental support for the hypothesis that some behaviors and physiological responses of giant clams exhibit 24-h rhythms, which are affected by changes of light/dark alternation.

The maximum rate at which fish can take up oxygen from their environment to fuel aerobic metabolism is an important feature of their physiology and ecology. Methods to quantify maximum oxygen uptake rate ( Ṁ O 2 ), therefore, should reliably and reproducibly estimate the highest possible Ṁ O 2 by an individual or species under a given set of conditions (peak Ṁ O 2 ). This study determined peak Ṁ O 2 and its repeatability in Gulf killifish, Fundulus grandis, subjected to three methods to elevate metabolism: swimming at increasing water speeds, during recovery after an exhaustive chase, and after ingestion of a large meal. Estimates of peak Ṁ O 2 during swimming and after an exhaustive chase were repeatable across two trials, whereas peak Ṁ O 2 after feeding was not. Peak Ṁ O 2 determined by the three methods was significantly different from one another, being highest during swimming, lowest after an exhaustive chase, and intermediate after feeding. In addition, peak Ṁ O 2 during recovery from an exhaustive chase depended on the length of time of recovery: in nearly 60% of the trials, values within the first hour of the chase were lower than those measured later. A novel and important finding was that an individual's peak Ṁ O 2 was not repeatable when compared across methods. Therefore, the peak Ṁ O 2 estimated for a group of fish, as well as the ranking of individual Ṁ O 2 within that group, depends on the method used to elevate aerobic metabolism.

The maximum rate at which fish can take up oxygen from their environment to fuel aerobic metabolism is an important feature of their physiology and ecology. Methods to quantify maximum oxygen uptake rate ( Ṁ O 2 ), therefore, should reliably and reproducibly estimate the highest possible Ṁ O 2 by an individual or species under a given set of conditions (peak Ṁ O 2 ). This study determined peak Ṁ O 2 and its repeatability in Gulf killifish, Fundulus grandis, subjected to three methods to elevate metabolism: swimming at increasing water speeds, during recovery after an exhaustive chase, and after ingestion of a large meal. Estimates of peak Ṁ O 2 during swimming and after an exhaustive chase were repeatable across two trials, whereas peak Ṁ O 2 after feeding was not. Peak Ṁ O 2 determined by the three methods was significantly different from one another, being highest during swimming, lowest after an exhaustive chase, and intermediate after feeding. In addition, peak Ṁ O 2 during recovery from an exhaustive chase depended on the length of time of recovery: in nearly 60% of the trials, values within the first hour of the chase were lower than those measured later. A novel and important finding was that an individual's peak Ṁ O 2 was not repeatable when compared across methods. Therefore, the peak Ṁ O 2 estimated for a group of fish, as well as the ranking of individual Ṁ O 2 within that group, depends on the method used to elevate aerobic metabolism.

Animals routinely encounter environmental (e.g., high temperatures and hypoxia) as well as physiological perturbations (e.g., exercise and digestion) that may threaten homeostasis. However, comparing the relative threat or “disruptiveness” imposed by different stressors is difficult, as stressors vary in their mechanisms, effects, and timescales. We exploited the fact that several acute stressors can induce the loss of equilibrium (LOE) in fish to (i) compare the metabolic recovery profiles of three environmentally relevant stressors and (ii) test the concept that LOE could be used as a physiological calibration for the intensity of different stressors. We focused on Etheostoma caeruleum, a species that routinely copes with environmental fluctuations in temperature and oxygen and that relies on burst swimming to relocate and avoid predators, as our model. Using stop‐flow (intermittent) respirometry, we tracked the oxygen consumption rate (MO 2 ) as E. caeruleum recovered from LOE induced by hypoxia (PO 2 at LOE), warming (critical thermal maximum, CT max ), or exhaustive exercise. Regardless of the stressor used, E. caeruleum recovered rapidly, returning to routine MO 2 within ~3 h. Fish recovering from hypoxia and warming had similar maximum MO 2, aerobic scopes, recovery time, and total excess post‐hypoxia or post‐warming oxygen consumption. Though exhaustive exercise induced a greater maximum MO 2 and corresponding higher aerobic scope than warming or hypoxia, its recovery profile was otherwise similar to the other stressors, suggesting that “calibration” to a physiological state such as LOE may be a viable conceptual approach for investigators interested in questions related to multiple stressors, cross tolerance, and how animals cope with challenges to homeostasis.

Heatwaves are becoming more frequent and intensified with climate change. Freshwater ecosystems are among the most threatened, within which, differing responses between cool- and warmwater species to heatwaves can lead to fundamental changes in communities. Physiological experiments can identify potential mechanisms underlying the impacts of such heatwaves on fish communities. In the current study, we quantified the oxygen consumption rate, aerobic scope and swimming performance of cool- and warmwater fish species following the simulation of short-term heatwaves currently occurring in streams in the Midwestern United States. The coolwater predator walleye (Sander vitreus) showed clear thermal disadvantages relative to the warmwater predator largemouth bass (Micropterus salmoides), based on a high metabolic cost during the heatwave, low metabolic activity when encountering prey, and reduced swimming performance following the heatwave. Largemouth bass also showed a thermal advantage relative to the warmwater prey fathead minnow (Pimephales promelas) related to swimming performance and energetic costs, highlighting differing thermal responses between predators and prey. This study demonstrates the importance of considering short-term extreme thermal events in the response of aquatic communities to climate stressors.

Behavioural, physiological and biochemical mechanisms constitute the adaptive capacities that allow marine ectotherms to explore the environment beyond their thermal optimal. Limitations to the efficiency of these mechanisms define the transition from moderate to severe thermal stress, and serve to characterise the thermoregulatory response in the zone of thermal tolerance. We selected a tropical population of Hippocampus erectus to describe the timing of the physiological and biochemical mechanisms in response to the following increments in water temperature: (i) 4°C abrupt (26–30°C in <5 min); (ii) 7°C abrupt (26–33°C); (iii) 4°C gradual (1°C every 3 h) and (iv) 7°C gradual (1.5°C every 3 h). The routine metabolic rate ( Rrout ) of juvenile H. erectus was measured immediately before and after 0.5, 12 and 28 h of being exposed to each thermal treatment. Samples of muscle and abdominal organs were taken to quantify indicators of aerobic and anaerobic metabolism and antioxidant enzymes and oxidative stress at each moment throughout exposure. Results showed a full thermoregulatory response within 0.5 h: Rrout increased in direct correspondence with both the magnitude and rate of thermal increase; peroxidised lipids rapidly accumulated before the antioxidant defence was activated and early lactate concentrations suggested an immediate, yet temporary, reduction in aerobic scope. After 12 h, Rrout had decreased in sea horses exposed to 30°C, but not to 33°C, where Rrout continued high until the end of trials. Within 28 h of thermal exposure, all metabolite and antioxidant defence indicators had been restored to control levels (26°C). These findings testify to the outstanding thermal plasticity of H. erectus and explain their adjustment to rapid fluctuations in ambient temperature. Such features, however, do not protect this tropical population from the deleterious effects of chronic exposure to temperatures that have been predicted for the future.

The yellowtail kingfish is a highly active and fast-growing marine fish with promising potential for aquaculture. In this study, essential insights were gained into the energy economy of this species by heart rate and acceleration logging during a swim-fitness test and a subsequent stress challenge test. Oxygen consumption values of the 600–800 g fish, when swimming in the range of 0.2 up to 1 m·s−1, were high—between 550 and 800 mg·kg−1·h−1—and the heart rate values—up to 228 bpm—were even among the highest ever measured for fishes. When swimming at these increasing speeds, their heart rate increased from 126 up to 162 bpm, and acceleration increased from 11 up to 26 milli-g. When exposed to four sequential steps of increasing stress load, the decreasing peaks of acceleration (baseline values of 12 to peaks of 26, 19 and 15 milli-g) indicated anticipatory behavior, but the heart rate increases (110 up to 138–144 bpm) remained similar. During the fourth step, when fish were also chased, peaking values of 186 bpm and 44 milli-g were measured. Oxygen consumption and heart rate increased with swimming speed and was well reflected by increases in tail beat and head width frequencies. Only when swimming steadily near the optimal swimming speed were these parameters strongly correlated.

Animals often experience changes in their environment that can be perceived as stressful. Previous evidence indicates that different individuals may have distinct stress responses. The role of serotonin (5-HT) in stress adaptation is well established, but its relationship with different defense strategies and the persistence of physiological and behavioral responses in different individuals during repeated acute stress remain unclear. In this study, using olive flounder (Paralichthys olivaceus) as a model, we analyzed the relationship between boldness and neurotransmitter 5-HT activity. We found that 5-HT suppression with 5-HT synthesis inhibitor p-chlorophenylalanine (pCPA) and 5-HT receptor subtype 1A (5-HT1A) antagonist WAY-100635 increased their oxygen consumption rates and the boldness of shy individuals. We determined the metabolic and behavioral changes in bold and shy individuals to repeated acute stress. The results suggest that bold individuals switch on passive “energy-saving” personality by changing their defense behavior from “fight-flight” to “freeze-hide” during a threat encounter, which manifests high behavioral plasticity. Both behavioral types decreased their spontaneous activity levels, which were also strengthened by limiting metabolic rate. Interestingly, treatment with pCPA and WAY-100635 before stress procedure attenuated stress and increased the boldness across diverse behavioral types. This study provides the initial empirical evidence of how perception of stress impacts both individual defense behavior and personality in this species. These findings can enhance our comprehension of individual variability and behavioral plasticity in animals, thereby improving our ability to develop effective adaptive management strategies.

Attempting to differentiate phenotypic variation caused by environmentally-induced alterations in gene expression from that caused by actual allelic differences can be experimentally difficult. Environmental variables must be carefully controlled and then interindividual genetic differences ruled out as sources of phenotypic variation. We investigated phenotypic variability of cardiorespiratory physiology as well as biometric traits in the parthenogenetically-reproducing marbled crayfish Procambarus virginalis Lyko, 2017, all offspring being genetically identical clones. Populations of P. virginalis were reared from eggs tank-bred at four different temperatures (16, 19, 22 and 25 °C) or two different oxygen levels (9.5 and 20 kPa). Then, at Stage 3 and 4 juvenile stages, physiological (heart rate, oxygen consumption) and morphological (carapace length, body mass) variables were measured. Heart rate and oxygen consumption measured at 23 °C showed only small effects of rearing temperature in Stage 3 juveniles, with larger effects evident in older, Stage 4 juveniles. Additionally, coefficients of variation were calculated to compare our data to previously published data on P. virginalis as well as sexually-reproducing crayfish. Comparison revealed that carapace length, body mass and heart rate (but not oxygen consumption) indeed showed lower, yet notable coefficients of variation in clonal crayfish. Yet, despite being genetically identical, significant variation in their morphology and physiology in response to different rearing conditions nonetheless occurred in marbled crayfish. This suggests that epigenetically induced phenotypic variation might play a significant role in asexual but also sexually reproducing species.

Carnivorous reptiles exhibit an intense metabolic increment during digestion, which is accompanied by several cardiovascular adjustments responsible for meeting the physiological demands of the gastrointestinal system. Postprandial tachycardia, a well-documented phenomenon in these animals, is mediated by the withdrawal of vagal tone associated with the chronotropic effects of non-adrenergic and non-cholinergic (NANC) factors. However, herbivorous reptiles exhibit a modest metabolic increment during digestion and there is no information about postprandial cardiovascular adjustments. Considering the significant impact of feeding characteristics on physiological responses, we investigated cardiovascular and metabolic responses, as well as the neurohumoral mechanisms of cardiac control, in the herbivorous lizard Iguana iguana during digestion. We measured oxygen consumption rate (O2), heart rate (fH), mean arterial blood pressure (MAP), myocardial activity, cardiac autonomic tone, fH/MAP variability and baroreflex efficiency in both fasting and digesting animals before and after parasympathetic blockade with atropine followed by double autonomic blockade with atropine and propranolol. Our results revealed that the peak of O2 in iguanas was reached 24 h after feeding, accompanied by an increase in myocardial activity and a subtle tachycardia mediated exclusively by a reduction in cardiac parasympathetic activity. This represents the first reported case of postprandial tachycardia in digesting reptiles without the involvement of NANC factors. Furthermore, this withdrawal of vagal stimulation during digestion may reduce the regulatory range for short-term fH adjustments, subsequently intensifying the blood pressure variability as a consequence of limiting baroreflex efficiency.

Freshwater ecosystems are undergoing rapid thermal shifts, making it increasingly important to understand species-specific responses to these changes. Traditional techniques for determining a species’ thermal tolerance are often lethal and time consuming. Using the enzyme activity associated with the electron transport system (ETS; hereafter referred to as enzyme assay) may provide a non-lethal, rapid, and efficient alternative to traditional techniques for some species. We used largemouth bass Micropterus salmoides (Lacepede, 1802) to test the efficacy of using an enzyme assay to determine thermal tolerance and respiratory exploitation in response to variable acclimation temperatures. Three tissue types were dissected from fish acclimated to 20, 25, or 30 °C and used in ETS assays at temperatures ranging from 7.5 to 40 °C. While there were significant differences among tissue types and acclimation temperatures, maximal enzyme activity occurred from 25.23 to 31.91 °C. Fish lost equilibrium at 39–42 °C in traditional CT max trials, significantly higher than the upper optimum range determined via enzyme assays. The ratio of enzyme activity to measured whole organism respiration rate decreased with increasing water temperature, with the largest changes occurring at the upper optimum thermal range determined by enzyme assays. Our results indicate that ETS analysis may prove useful for obtaining biologically relevant thermal tolerances.

Overharvesting is a serious threat to many fish populations. High mortality and directional selection on body size can cause evolutionary change in exploited populations via selection for a specific phenotype and a potential reduction in phenotypic diversity. Whether the loss of phenotypic diversity that accompanies directional selection impairs response to environmental stress is not known. To address this question, we exposed three zebrafish selection lines to thermal stress. Two lines had experienced directional selection for (1) large and (2) small body size, and one was (3) subject to random removal of individuals with respect to body size (i.e. line with no directional selection). Selection lines were exposed to three temperatures (elevated, 34°C; ambient, 28°C; low, 22°C) to determine the response to an environmental stressor (thermal stress). We assessed differences among selection lines in their life history (growth and reproduction), physiological traits (metabolic rate and critical thermal max) and behaviour (activity and feeding behaviour) when reared at different temperatures. Lines experiencing directional selection (i.e. size selected) showed reduced growth rate and a shift in average phenotype in response to lower or elevated thermal stress compared with fish from the random‐selected line. Our data indicate that populations exposed to directional selection can have a more limited capacity to respond to thermal stress compared with fish that experience a comparable reduction in population size (but without directional selection). Future studies should aim to understand the impacts of environmental stressors on natural fish stocks.

Sustained swimming induces beneficial effects on growth and energy metabolism in some fish species. However, the absence of a standardized exercise regimen that guarantees an optimal response to physical activity is due to the anatomical, behavioral, and physiological differences among species, and the different conditions of tests applied, which are especially notable for the early stages of cultured species. The objective of this study was to assess the growth and metabolic responses of European sea bass submitted to continuous and moderate exercise exposure, selecting a practical swimming speed from swimming tests of groups of five fingerlings. The exercise-effects trial was carried out with 600 sea bass fingerlings (3–5 g body weight) distributed in two groups (control: voluntary swimming; exercised: under sustained swimming at 1.5 body lengths·s−1). After 6 weeks, growth parameters and proximal composition of both muscles were not altered by sustained swimming, but an increased synthetic capacity (increased RNA/DNA ratio) and more efficient use of proteins (decreased ΔN15) were observed in white muscle. The gene expression of mitochondrial proteins in white and red muscle was not affected by exercise, except for ucp3, which increased. The increase of UCP3 and Cox4 protein expression, as well as the higher COX/CS ratio of enzyme activity in white muscle, pointed out an enhanced oxidative capacity in this tissue during sustained swimming. In the protein expression of red muscle, only CS increased. All these metabolic adaptations to sustained exercise were also reflected in an enhanced maximum metabolic rate (MMR) with higher aerobic scope (AMS) of exercised fish in comparison to the non-trained fish, during a swimming test. These results demonstrated that moderate sustained swimming applied to sea bass fingerlings can improve the physical fitness of individuals through the enhancement of their aerobic capacities.

In variable environments, repeatable phenotypic differences between individuals provide the variation required for natural selection. The pace-of-life syndrome (POLS) provides a conceptual framework linking individual physiology and life histories to behaviour, where rapidly growing individuals demonstrate higher rates of resting or “standard” metabolic rate (SMR). If differences in SMR are consistent between fast- and slow-growing individuals, these differences may be important to capture in bioenergetic relationships used to describe their growth, energy acquisition, and allocation. We compared growth rates and SMR between a domesticated and wild strain of rainbow trout ( Oncorhynchus mykiss (Walbaum, 1792)) using intermittent flow respirometry. Though mass-scaling exponents were similar between strains, mass-scaling coefficients of SMR for fast-growing rainbow trout were 1.25 times higher than those for slower growing fish. These observed differences in mass-scaling coefficients between fast- and slow-growing rainbow trout were consistent with data extracted from several other studies. Bioenergetic estimates of consumption for domestic strain fish increased as the difference in SMR and wild strain fish increased, and increased as activity level increased. Our results indicate patterns of SMR consistent with POLS, and suggest that strain-specific SMR equations may be important for applications to active populations (i.e., field observations).

Tacrolimus (FK506) is a common immunosuppressant that is used in organ transplantation. However, despite its importance in medical applications, it is prone to adverse side effects. While some studies have demonstrated its toxicities to humans and various animal models, very few studies have addressed this issue in aquatic organisms, especially zebrafish. Here, we assessed the adverse effects of acute and chronic exposure to tacrolimus in relatively low doses in zebrafish in both larval and adult stages, respectively. Based on the results, although tacrolimus did not cause any cardiotoxicity and respiratory toxicity toward zebrafish larvae, it affected their locomotor activity performance in light–dark locomotion tests. Meanwhile, tacrolimus was also found to slightly affect the behavior performance, shoaling formation, circadian rhythm locomotor activity, and color preference of adult zebrafish in a dose-dependent manner. In addition, alterations in the cognitive performance of the fish were also displayed by the treated fish, indicated by a loss of short-term memory. To help elucidate the toxicity mechanism of tacrolimus, molecular docking was conducted to calculate the strength of the binding interaction between tacrolimus to human FKBP12. The results showed a relatively normal binding affinity, indicating that this interaction might only partly contribute to the observed alterations. Nevertheless, the current research could help clinicians and researchers to further understand the toxicology of tacrolimus, especially to zebrafish, thus highlighting the importance of considering the toxicity of tacrolimus prior to its usage.

Understanding how metabolic costs change in relation to increasing temperature under future climate changes is important to predict how ectotherms will be affected across the globe. In fish, whole body respiration is traditionally used to estimate aerobic performance via an organism’s minimum and maximum oxygen consumption rates. However, mitochondria play a crucial role in the aerobic cascade and may be a useful surrogate of aerobic performance. To test whether whole body oxygen consumption and mitochondrial capacity are correlated, we estimated whole body metabolic and mitochondrial respiration rates (using permeabilized red muscle fibres) in brook trout ( Salvelinus fontinalis (Mitchill, 1814)) at 10, 15, and 20 °C. Standard metabolic rate increased with acclimation temperature, while maximum rates were less sensitive. All mitochondrial respiration rates increased with acclimation temperature, suggesting that red muscle mitochondrial preparations may correlate to the minimal metabolic demands in this species. When expressed as relative rates of electron flow, the red muscle fibres showed no effect of temperature on mitochondrial coupling efficiency. However, there was a pattern of declining capacity to augment respiration via complex II with increasing temperature with a concomitant increase in the capacity of the phosphorylating system relative to maximal rates of mitochondrial electron flow.

To ensure optimal feed intake, growth, and general fish health in aquaculture sea cages, interactions between drivers that affect oxygen conditions need to be understood. The main drivers are oxygen consumption and water exchange, caused by flow through the cage. Swimming energetics in rainbow trout (Oncorhynchus mykiss) in normoxia and hypoxia at 10, 15, and 20 °C were determined. Using the determinations, a conceptual model of oxygen conditions within sea cages was created. By applying the model to a case study, results show that with a temperature increase of 10 °C, oxygen concentration will decrease three times faster. To maintain optimal oxygen concentration within the cage, the flow velocity must be increased by a factor of 3.7. The model is highly relevant for current farms since the model predictions can explain why and when suboptimal conditions occur within the cages. Using the same method, the model can be used to estimate the suitability of potential new aquaculture sites.

Alcoholic myopathy is caused by chronic consumption of alcohol (ethanol) and is characterized by weakness and atrophy of skeletal muscle. Regular exercise is one of the important ways to prevent or alleviate skeletal muscle myopathy. However, the beneficial effects and the exact mechanisms underlying regular exercise on alcohol myopathy remain unclear. In this study, a model of alcoholic myopathy was established using zebrafish soaked in 0.5% ethanol. Additionally, these zebrafish were intervened to swim for 8 weeks at an exercise intensity of 30% of the absolute critical swimming speed (Ucrit), aiming to explore the beneficial effects and underlying mechanisms of regular exercise on alcoholic myopathy. This study found that regular exercise inhibited protein degradation, improved locomotion ability, and increased muscle fiber cross-sectional area (CSA) in ethanol-treated zebrafish. In addition, regular exercise increases the functional activity of mitochondrial respiratory chain (MRC) complexes and upregulates the expression levels of MRC complexes. Regular exercise can also improve oxidative stress and mitochondrial dynamics in zebrafish skeletal muscle induced by ethanol. Additionally, regular exercise can activate mitochondrial biogenesis and inhibit mitochondrial unfolded protein response (UPRmt). Together, our results suggest regular exercise is an effective intervention strategy to improve mitochondrial homeostasis to attenuate alcoholic myopathy.

A fundamental issue in the metabolic field is whether it is possible to understand underlying mechanisms that characterize individual variation. Whole-animal performance relies on mitochondrial function as it produces energy for cellular processes. However, our lack of longitudinal measures to evaluate how mitochondrial function can change within and among individuals and with environmental context makes it difficult to assess individual variation in mitochondrial traits. The aims of this study were to test the repeatability of muscle mitochondrial metabolism by performing two biopsies of red muscle, and to evaluate the effects of biopsies on whole-animal performance in goldfish Carassius auratus. Our results show that basal mitochondrial respiration and net phosphorylation efficiency are repeatable at 14-day intervals. We also show that swimming performance (optimal cost of transport and critical swimming speed) was repeatable in biopsied fish, whereas the repeatability of individual oxygen consumption (standard and maximal metabolic rates) seemed unstable over time. However, we noted that the means of individual and mitochondrial traits did not change over time in biopsied fish. This study shows that muscle biopsies allow the measurement of mitochondrial metabolism without sacrificing animals and that two muscle biopsies 14 days apart affect the intraspecific variation in fish performance without affecting average performance of individuals. This article is part of the theme issue ‘The evolutionary significance of variation in metabolic rates’.

Metabolic rates are linked to key life-history traits that are thought to set the pace of life and affect fitness, yet the role that parents may have in shaping the metabolism of their offspring to enhance survival remains unclear. Here, we investigated the effect of temperature (24°C or 30°C) and feeding frequency experienced by parent zebrafish ( Danio rerio ) on offspring phenotypes and early survival at different developmental temperatures (24°C or 30°C). We found that embryo size was larger, but survival lower, in offspring from the parental low food treatment. Parents exposed to the warmer temperature and lower food treatment also produced offspring with lower standard metabolic rates—aligning with selection on embryo metabolic rates. Lower metabolic rates were correlated with reduced developmental and growth rates, suggesting selection for a slow pace of life. Our results show that intergenerational phenotypic plasticity on offspring size and metabolic rate can be adaptive when parent and offspring temperatures are matched: the direction of selection on embryo size and metabolism aligned with intergenerational plasticity towards lower metabolism at higher temperatures, particularly in offspring from low-condition parents. These findings provide evidence for adaptive parental effects, but only when parental and offspring environments match.

Across diverse taxa, sublethal exposure to abiotic stressors early in life can lead to benefits such as increased stress tolerance upon repeat exposure. This phenomenon, known as hormetic priming, is largely unexplored in early life stages of marine invertebrates, which are increasingly threatened by anthropogenic climate change. To investigate this phenomenon, larvae of the sea anemone and model marine invertebrate Nematostella vectensis were exposed to control (18 °C) or elevated (24 °C, 30 °C, 35 °C, or 39 °C) temperatures for 1 h at 3 days post-fertilization (DPF), followed by return to control temperatures (18 °C). The animals were then assessed for growth, development, metabolic rates, and heat tolerance at 4, 7, and 11 DPF. Priming at intermediately elevated temperatures (24 °C, 30 °C, or 35 °C) augmented growth and development compared to controls or priming at 39 °C. Indeed, priming at 39 °C hampered developmental progression, with around 40% of larvae still in the planula stage at 11 DPF, in contrast to 0% for all other groups. Total protein content, a proxy for biomass, and respiration rates were not significantly affected by priming, suggesting metabolic resilience. Heat tolerance was quantified with acute heat stress exposures, and was significantly higher for animals primed at intermediate temperatures (24 °C, 30 °C, or 35 °C) compared to controls or those primed at 39 °C at all time points. To investigate a possible molecular mechanism for the observed changes in heat tolerance, the expression of heat shock protein 70 (HSP70) was quantified at 11 DPF. Expression of HSP70 significantly increased with increasing priming temperature, with the presence of a doublet band for larvae primed at 39 °C, suggesting persistent negative effects of priming on protein homeostasis. Interestingly, primed larvae in a second cohort cultured to 6 weeks post-fertilization continued to display hormetic growth responses, whereas benefits for heat tolerance were lost; in contrast, negative effects of short-term exposure to extreme heat stress (39 °C) persisted. These results demonstrate that some dose-dependent effects of priming waned over time while others persisted, resulting in heterogeneity in organismal performance across ontogeny following priming. Overall, these findings suggest that heat priming may augment the climate resilience of marine invertebrate early life stages via the modulation of key developmental and physiological phenotypes, while also affirming the need to limit further anthropogenic ocean warming.

Spring conditions, especially in temperate regions, may fluctuate abruptly and drastically. Environmental variability can expose organisms to temperatures outside of their optimal thermal ranges. For ectotherms, sudden changes in temperature may cause short- and long-term physiological effects, including changes in respiration, morphology, and reproduction. Exposure to variable temperatures during active development, which is likely to occur for insects developing in spring, can cause detrimental effects. Using the alfalfa leafcutting bee, Megachile rotundata, we aimed to determine if oxygen consumption could be measured using a new system and to test the hypothesis that female and male M. rotundata have a thermal performance curve with a wide optimal range. Oxygen consumption of M. rotundata pupae was measured across a large range of temperatures (6–48°C) using an optical oxygen sensor in a closed respirometry system. Absolute and mass-specific metabolic rates were calculated and compared between bees that were extracted from their brood cells and those remaining in the brood cell to determine whether pupae could be accurately measured inside their brood cells. The metabolic response to temperature was non-linear, which is an assumption of a thermal performance curve; however, the predicted negative slope at higher temperatures was not observed. Despite sexual dimorphism in body mass, sex differences only occurred in mass-specific metabolic rates. Higher metabolic rates in males may be attributed to faster development times, which could explain why there were no differences in absolute metabolic rate measurements. Understanding the physiological and ecological effects of thermal environmental variability on M. rotundata will help to better predict their response to climate change.

Phenotypes that allow animals to detect, weather, and predict changes efficiently are essential for survival in fluctuating environments. Some phenotypes may remain specialized to suit an environment perfectly, while others become more plastic or generalized, shifting flexibly to match current context or adopting a form that can utilize a wide range of contexts. Here, we tested the differences in behavior, morphology, sensory and metabolic physiology between wild zebrafish (Danio rerio) in highly variable fast-flowing rivers and still-water sites. We found that river zebrafish moved at higher velocities than did still-water fish, had lower oxygen demands, and responded less vigorously to small changes in flow rate, as we might expect for fish that are well-suited to high-flow environments. River zebrafish also had less streamlined bodies and were more behaviorally plastic than were still-water zebrafish, both features that may make them better-suited to a transitional lifestyle. Our results suggest that zebrafish use distinct sensory mechanisms and metabolic physiology to reduce energetic costs of living in fast-flowing water while relying on morphology and behavior to create flexible solutions to a challenging habitat. Insights on animals’ reliance on traits with different outcomes provide a framework to better understand their survival in future environmental fluctuations.

Fenpropathrin, a pyrethroid insecticide, has been widely used for many years in agricultural fields. It works by disturbing the voltage-gated sodium channel, leading to paralysis and the death of the target animal. While past studies have focused on neurodegeneration following fenpropathrin poisoning in humans, relatively few pieces of research have examined its effect on other peripheral organs. This study successfully investigated the potential toxicity of fenpropathrin on the cardiovascular system using zebrafish as an animal model. Zebrafish larvae exposed to varying doses of fenpropathrin underwent an evaluation of cardiac physiology by measuring the heart rate, stroke volume, cardiac output, and shortening fraction. The blood flow velocity and the dorsal aorta diameter were also measured to assess the impact of fenpropathrin exposure on the vascular system. Furthermore, molecular docking was performed to evaluate the pesticide binding affinity to various proteins associated with the cardiovascular system, revealing the potential mechanism of the fenpropathrin cardiotoxic effect. The findings demonstrated a significant dose-dependent increase in the heart rate stroke volume, cardiac output, shortening fraction, and ejection fraction of zebrafish larvae after 24 h of acute treatment with fenpropathrin. Additionally, zebrafish treated at a concentration of 1 ppm exhibited significantly larger blood vessels in diameter and an increased blood flow velocity compared to the control group. According to molecular docking, fenpropathrin showed a high affinity for various voltage-gated sodium channels like scn1lab, cacna1sb, and clcn3. Finally, from the results, we found that fenpropathrin caused cardiomegaly, which may have been induced by the voltage-gated sodium channel disruption. This study highlights the significant disruption of fenpropathrin in the cardiovascular system and emphasizes the need for further research on the health implications of this pesticide.

Teleost fish have evolved various adaptations that allow them to tolerate cold water conditions. However, the underlying mechanism of this adaptation is poorly understood in Tibetan Plateau fish. RNA-seq combined with liquid chromatography‒mass spectrometry (LC‒MS/MS) metabolomics was used to investigate the physiological responses of a Tibetan Plateau-specific teleost, Gymnocypris przewalskii, under cold conditions. The 8-month G. przewalskii juvenile fish were exposed to cold (4 ℃, cold acclimation, CA) and warm (17 ℃, normal temperature, NT) temperature water for 15 days. Then, the transcript profiles of eight tissues, including the brain, gill, heart, intestine, hepatopancreas, kidney, muscle, and skin, were evaluated by transcriptome sequencing. The metabolites of the intestine, hepatopancreas, and muscle were identified by LC‒MS/MS. A total of 5,745 differentially expressed genes (DEGs) were obtained in the CA group. The key DEGs were annotated using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis. The DEGs from the eight tissues were significantly enriched in spliceosome pathways, indicating that activated alternative splicing is a critical biological process that occurs in the tissues to help fish cope with cold stress. Additionally, 82, 97, and 66 differentially expressed metabolites were identified in the intestine, hepatopancreas, and muscle, respectively. Glutathione metabolism was the only overlapping significant pathway between the transcriptome and metabolome analyses in these three tissues, indicating that an activated antioxidative process was triggered during cold stress. In combination with the multitissue transcriptome and metabolome, we established a physiology-gene‒metabolite interaction network related to energy metabolism during cold stress and found that gluconeogenesis and long-chain fatty acid metabolism played critical roles in glucose homeostasis and energy supply.

All freshwater organisms are challenged to control their internal balance of water and ions in strongly hypotonic environments. We compared the influence of external salinity on the oxygen consumption rates (ṀO2) of three species of freshwater insects, one snail and two crustaceans. Consistent with available literature, we found a clear decrease in ṀO2 with increasing salinity in the snail Elimia sp. and crustaceans Hyalella azteca and Gammarus pulex (r5=−0.90, P=0.03). However, we show here for the first time that metabolic rate was unchanged by salinity in the aquatic insects, whereas ion transport rates were positively correlated with higher salinities. In contrast, when we examined the ionic influx rates in the freshwater snail and crustaceans, we found that Ca uptake rates were highest under the most dilute conditions, while Na uptake rates increased with salinity. In G. pulex exposed to a serially diluted ion matrix, Ca uptake rates were positively associated with ṀO2 (r5=−0.93, P=0.02). This positive association between Ca uptake rate and ṀO2 was also observed when conductivity was held constant but Ca concentration was manipulated (1.7–17.3 mg Ca l−1) (r5=0.94, P=0.05). This finding potentially implicates the cost of calcium uptake as a driver of increased metabolic rate under dilute conditions in organisms with calcified exoskeletons and suggests major phyletic differences in osmoregulatory physiology. Freshwater insects may be energetically challenged by higher salinities, while lower salinities may be more challenging for other freshwater taxa.

One of the hallmarks of invasive species is their propensity to spread. Removing an invasive species after establishment is virtually impossible, and so considerable effort is invested in preventing the range expansion of invaders. Silver carp were discovered in the Mississippi River in 1981 and have spread throughout the basin. Despite their propensity to expand, the ‘leading edge’ in the Illinois River has stalled south of Chicago, and has remained stable for a decade. Studies have suggested that pollutants in the Chicago Area Waterway System (CAWS) may be contributing to the lack of upstream movement, but this hypothesis has not been tested. This study used a laboratory setting to quantify the role of pollutants in deterring upstream movement of silver carp within the CAWS. For this, water was collected from the CAWS near the upstream edge of the distribution and transported to a fish culture facility. Silver carp and one native species were exposed to CAWS water, and activity, behavior, avoidance and metabolic rates were quantified. Results showed that silver carp experience an elevated metabolic cost in CAWS water, along with reductions in swimming behavior. Together, results suggest a role for components of CAWS water at deterring range expansion.

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-quinone) is a degradation product of 6PPD, an antioxidant widely used in rubber tires. 6PPD-quinone enters aquatic ecosystems through urban stormwater runoff and has been identified as the chemical behind the urban runoff mortality syndrome in coho salmon. However, the available data suggest that the acute effects of 6PPD-quinone are restricted to a few salmonid species and that the environmental levels of this chemical should be safe for most fish. In this study, larvae of a "tolerant" fish species, Danio rerio, were exposed to three environmental concentrations of 6PPD-quinone for only 24 h, and the effects on exploratory behavior, escape response, nonassociative learning (habituation), neurotransmitter profile, wake/sleep cycle, circadian rhythm, heart rate and oxygen consumption rate were analyzed. Exposure to the two lowest concentrations of 6PPD-quinone resulted in altered exploratory behavior and habituation, an effect consistent with some of the observed changes in the neurotransmitter profile, including increased levels of acetylcholine, norepinephrine, epinephrine and serotonin. Moreover, exposure to the highest concentration tested altered the wake/sleep cycle and the expression of per1a, per3 and cry3a, circadian clock genes involved in the negative feedback loop. Finally, a positive chronotropic effect of 6PPD-quinone was observed in the hearts of the exposed fish. The results of this study emphasize the need for further studies analyzing the effects of 6PPD-quinone in "tolerant" fish species.

Many salmonid species are particularly susceptible to chronic and acute temperature changes caused by global warming. We aimed to study the differences in metabolic and transcriptomic responses of a chronic heat stress on a control and selected (absence of early sexual maturation and growth) line of brook charr Salvelinus fontinalis (Mitchill, 1814). We exposed individuals to different temperatures for 35 days (15, 17, and 19 °C). High temperature reduced the growth rate (in length) and the Fulton condition factor. Both maximal metabolic rate and the aerobic scope were higher in fish reared at 17 °C, while they decreased in fish maintained at 19 °C. The relative gene expression of cytochrome c oxidase was lower at 19 °C than at 15 °C. The relative gene expressions of both liver and gill hsp90 was higher at the highest temperature. The standard metabolic rate, while not affected by temperature, was higher for the control line over the selected line. Only in the control line, the relative expression of catalase and of receptor of insulin-like growth factor-1 increased at 19 °C. Our results showed that the selected line was able to cope more effectively with the oxidative stress caused by the rise in temperature.

Species with a wide distribution can experience significant regional variation in environmental conditions, to which they can acclimatize or adapt. Consequently, the geographic origin of an organism can influence its responses to environmental changes, and therefore its sensitivity to combined global change drivers. This study aimed at determining the physiological responses of the northern shrimp, Pandalus borealis, at different levels of biological organization and from four different geographic origins, exposed to elevated temperature and low pH to define its sensitivity to future ocean warming and acidification. Shrimp sampled within the northwest Atlantic were exposed for 30 days to combinations of three temperature (2, 6 or 10°C) and two pH levels (7.75 or 7.40). Survival, metabolic rates, whole-organism aerobic performance and cellular energetic capacity were assessed at the end of the exposure. Our results show that shrimp survival was negatively affected by temperature above 6°C and low pH, regardless of their origin. Additionally, shrimp from different origins show overall similar whole-organism performances: aerobic scope increasing with increasing temperature and decreasing with decreasing pH. Finally, the stability of aerobic metabolism appears to be related to cellular adjustments specific to shrimp origin. Our results show that the level of intraspecific variation differs among levels of biological organization: different cellular capacities lead to similar individual performances. Thus, the sensitivity of the northern shrimp to ocean warming and acidification is overall comparable among origins. Nonetheless, shrimp vulnerability to predicted global change scenarios for 2100 could differ among origins owing to different regional environmental conditions.

Physiological and behavioral traits of aquatic organisms are often highly dependent on environmental conditions, but genetic (family) effects often contribute to phenotypic variation. In this study, a series of physiological indices were used to assess the variability that exists among progeny of lake sturgeon ( Acipenser fulvescens Rafinesque, 1817) produced from eight different families. We designed a controlled experiment aimed to evaluate metabolic performance of age-0 lake sturgeon where growth, energy density, survival, metabolic rate, volitional swimming performance, and critical thermal maxima were quantified for fish reared under the same environmental conditions. We found a strong family effect for most metrics that were quantified and primarily influenced by the female. Furthermore, poor growth and survival within families were strongly correlated to low energy density levels and depressed routine metabolic rates at the yolk sac stage. Lastly, the quantification of energy density at the onset of exogenous feeding appeared to be an excellent predictor of future growth and survival. Our results suggest that the choice of female for production of progeny in conservation hatcheries will have significant impacts on the success of stock enhancement as a conservation strategy for lake sturgeon.

Unionid mussels are imperiled worldwide. Understanding the impacts of thermal and hypoxia stress on larval (glochidia) and adult physiology is critical for understanding the potential impacts of climate change. We tested whether brood viability (proportion of glochidia competent to attach to a host) was correlated with oxygen demand (MO 2 ), ability to regulate oxygen consumption (regulation index (RI)), and/or critical dissolved oxygen concentration (DO crit ). We then examined the effects of temperature on MO 2, RI, and DO crit. The results were coupled with a previous study to estimate the fraction of brooding female oxygen demand comprised of glochidial respiration. We found little evidence that respiratory patterns of glochidia changed with declining brood viability, but strong evidence for decreasing glochidial RI and increasing DO crit with increasing temperatures. Glochidial respiration temperature coefficient ( Q 10 ) values were approximately 2–3× those estimated for brooding females, indicating greater temperature sensitivity. The proportion of gravid female respiration comprised of glochidial respiration reached its maximum at temperatures (23–28 °C) coinciding with brood expulsion. These patterns suggest high temperatures may have deleterious effects on unionids by decreasing the hypoxia tolerance of glochidia, increasing the rate at which glochidia deplete energy reserves, and increasing the proportion of oxygen consumption by gravid females that is comprised of glochidial oxygen demand.

Near-future climate change projections predict an increase in sea surface temperature that is expected to have significant and rapid effects on marine ectotherms, potentially affecting a number of critical life processes. Also, some habitats undergo more thermal variability than others and the inhabitants thereof must be more tolerant to acute periods of extreme temperatures. Mitigation of these outcomes may occur through acclimation, plasticity, or adaptation, although the rate and extent of a species' ability to adjust to warmer temperatures is largely unknown, specifically as it pertains to effects on various performance metrics in fishes that inhabit multiple habitats throughout ontogenetic stages. Here, the thermal tolerance and aerobic performance of schoolmaster snapper (Lutjanus apodus Walbaum, 1792) collected from two different habitats were experimentally assessed under different warming scenarios (temperature treatments = 30, 33, 35, 36° C) to assess vulnerability to an imminently changing thermal habitat. Larger subadult and adult fish collected from a 12 m deep coral reef exhibited a lower critical thermal maximum (CTmax ) compared to smaller juvenile fish collected from a 1 m deep mangrove creek. However, CTmax of the creek-sampled fish was only 2° C above the maximum water temperature measured in the habitat from which they were collected, compared to a CTmax that was 8° C higher in the reef-sampled fish, resulting in a wider thermal safety margin at the reef site. A GLM showed a marginally significant effect of temperature treatment on resting metabolic rate (RMR) but there were no effects on any of the tested factors on maximum metabolic rate (MMR) or absolute aerobic scope (AAS). Post-hoc tests revealed that RMR was significantly higher for creek-collected fish at the 36° C treatment and significantly higher for reef-collected fish at 35° C. Swimming performance (measured by critical swimming speed [Ucrit ]) was significantly lower at the highest temperature treatment for creek-collected fish and trended down with each successive increase in temperature treatment for reef-collected fish. These results show that metabolic rate and swimming performance responses to thermal challenges are somewhat consistent across collection habitats, and this species may be susceptible to unique types of thermal risk depending on its habitat. We show the importance of intraspecific studies that couple habitat profiles and performance metrics to better understand possible outcomes under thermal stress. This article is protected by copyright. All rights reserved.

Mesophotic reefs have been proposed as climate change refugia but are not synonymous ecosystems with shallow reefs and remain exposed to anthropogenic impacts. Planulae from the reef-building coral Stylophora pistillata, Gulf of Aqaba, from 5- and 45-m depth were tested ex situ for capacity to settle, grow, and acclimate to reciprocal light conditions. Skeletons were scanned by phase contrast-enhanced micro-CT to study morphology. Deep planulae had reduced volume, smaller diameter on settlement, and greater algal symbiont density. Light conditions did not have significant impact on settlement or mortality rates. Photosynthetic acclimation of algal symbionts was evident within 21-35 days after settlement but growth rate and polyp development were slower for individuals translocated away from their parental origin compared to controls. Though our data reveal rapid symbiont acclimation, reduced growth rates and limited capacity for skeletal modification likely limit the potential for mesophotic larvae to settle on shallow reefs.

Laboratory‐based studies examining fish physiological and behavioural responses to temperature can provide important insight into species‐specific habitat preferences and utilisation, and are especially useful in examining vulnerable life stages that are difficult to study in the wild. This study couples shuttle box behavioural experiments with respirometry trials to determine the temperature preferences and metabolic thermal sensitivity of juvenile California horn shark ( Heterodontus francisci ) and leopard shark ( Triakis semifasciata ). As juveniles, these two species often occupy similar estuarine habitats but display contrasting behaviours and activity levels – H. francisci are relatively sedentary, whereas T. semifasciata are more active and mobile. This study shows that juvenile H. francisci and T. semifasciata have comparable thermal preferences and occupy similar temperature ranges, but H. francisci metabolism is more sensitive to acute changes in temperature as expressed through a higher Q 10 ( H. francisci = 2.58; T. semifasciata = 1.97; temperature range: 12–24°C). Underlying chronic temperature acclimation to both warm (21°C) and cool (15°C) representative seasonal temperatures did not appear to significantly affect these parameters. These results are discussed in the context of field studies examining known distributions, habitat and movement patterns of H. francisci and T. semifasciata to better understand the role of temperature in species‐specific behaviour. Juvenile H. francisci likely target thermally stable environments, such as estuaries that are close to their preferred temperature, whereas juvenile T. semifasciata metabolism and behaviour appear less dependent on temperature.

The moon jellyfish Aurelia coerulea is the most common blooming scyphozoan jellyfish in global coastal waters. A. coerulea polyps can rapidly increase their population through asexual reproduction, which is influenced directly by the ambient seawater temperature. However, the physiological responses of A. coerulea polyps to future elevated seasonal seawater temperature scenarios are largely unknown. In this study, we performed an experiment to test the hypothesis that the elevated seasonal seawater temperatures (current seawater temperatures + 3°C) will increase the asexual reproduction, feeding, and respiration rates of A. coerulea polyps. After 42 days of exposure, the asexual reproduction and feeding rates of the A. coerulea polyps increased under the elevated seawater temperatures predicted for all seasons. The highest asexual reproduction rates occurred in predicted average summer seawater temperatures. The respiration rates of A. coerulea polyps were suppressed significantly under winter temperature conditions, suggesting that more available energy was allocated to asexual reproduction than to metabolism after warming. Overall, this study suggests that A. coerulea polyp populations will benefit from the predicted higher seawater temperatures in all four seasons, thereby further increasing the potential and scale of A. coerulea blooms.

Oceanic absorption of atmospheric CO2 results in alterations of carbonate chemistry, a process coined ocean acidification (OA). The economically and ecologically important eastern oyster (Crassostrea virginica) is vulnerable to these changes because low pH hampers CaCO3 precipitation needed for shell formation. Organisms have a range of physiological mechanisms to cope with altered carbonate chemistry; however, these processes can be energetically expensive and necessitate energy reallocation. Here, the hypothesis that resilience to low pH is related to energy resources was tested. In laboratory experiments, oysters were reared or maintained at ambient (400 ppm) and elevated (1300 ppm) pCO2 levels during larval and adult stages, respectively, before the effect of acidification on metabolism was evaluated. Results showed that oysters exposed to elevated pCO2 had significantly greater respiration. Subsequent experiments evaluated if food abundance influences oyster response to elevated pCO2. Under high food and elevated pCO2 conditions, oysters had less mortality and grew larger, suggesting that food can offset adverse impacts of elevated pCO2, while low food exacerbates the negative effects. Results also demonstrated that OA induced an increase in oyster ability to select their food particles, likely representing an adaptive strategy to enhance energy gains. While oysters appeared to have mechanisms conferring resilience to elevated pCO2, these came at the cost of depleting energy stores, which can limit the available energy for other physiological processes. Taken together, these results show that resilience to OA is at least partially dependent on energy availability, and oysters can enhance their tolerance to adverse conditions under optimal feeding regimes.

In many fish species, ontogenetic dietary shifts cause changes in both quantitative and qualitative intake of energy, and these transitions can act as significant bottlenecks in survival within a given year class. In the present study, we estimated routine metabolic rate (RMR) and forced maximum metabolic rate (FMR) in age 0 lake sturgeon ( Acipenser fulvescens ) on a weekly basis from 6 to 76 days posthatch (dph) within the same cohort of fish. We were particularly interested in the period of dietary transition from yolk to exogenous feeding between 6 and 17 dph and as the fish transitioned from an artemia-based diet to a predominantly bloodworm diet between 49 and 67 dph. Measurement of growth rate and energy density throughout indicated that there was a brief period of growth arrest during the transition from artemia to bloodworm. The highest mass-specific RMR (mg O 2 kg -1 h -1 ) recorded throughout the first 76 d of development occurred during the yolk sac phase and during transition from artemia to bloodworm. Similarly, diet transition from artemia to bloodworm-when growth arrest was observed-increased scaled RMR (i.e., mg O 2 kg -0.89 h -1 ), and it did not significantly differ from scaled FMR. Log-log relationships between non-mass-specific RMR or FMR (i.e., mg O 2 h -1 ) and body mass significantly changed as the growing fish adapted to the nutritional differences of their primary diet. We demonstrate that dietary change during early ontogeny has consequences for growth that may reflect altered metabolic performance. Results have implications for understanding cohort and population dynamics during early life and effective management for conservation fish hatcheries.

Energetic cost of growth determines how much food-derived energy is needed to produce a given amount of new biomass and thereby influences energy transduction between trophic levels. Growth and development are regulated by hormones and are therefore sensitive to changes in temperature and environmental endocrine disruption. Here, we show that the endocrine disruptor bisphenol A (BPA) at an environmentally relevant concentration (10 µgl −1 ) decreased fish ( Danio rerio ) size at 30°C water temperature. Under the same conditions, it significantly increased metabolic rates and the energetic cost of growth across development. By contrast, BPA decreased the cost of growth at cooler temperatures (24°C). BPA-mediated changes in cost of growth were not associated with mitochondrial efficiency (P/O ratios (i.e. adenosine diphosphate (ADP) used/oxygen consumed) and respiratory control ratios) although BPA did increase mitochondrial proton leak. In females, BPA decreased age at maturity at 24°C but increased it at 30°C, and it decreased the gonadosomatic index suggesting reduced investment into reproduction. Our data reveal a potentially serious emerging problem: increasing water temperatures resulting from climate warming together with endocrine disruption from plastic pollution can impact animal growth efficiency, and hence the dynamics and resilience of animal populations and the services these provide.

Macroinvertebrates that rely on a supply of planktonic larvae for recruitment play a significant role in maintaining productivity in mangrove ecosystems. Thus, identifying the spatial distribution and physiological limitations of invertebrate larval communities within mangroves is important for targeted conservation efforts to maintain population persistence amid the threat of climate change. Here, the role of spatial, lunar, and environmental factors in structuring invertebrate larval communities in Ting Kok, the second largest mangrove forest in Hong Kong, was examined. Results indicate that, spatially, invertebrate larval communities were influenced by environmental filtering, habitat type, and the lunar tidal cycle. This indicates the fundamental role of habitat heterogeneity and connectivity for the transport, distribution, and development of crustacean larvae. Larvae of key sesarmids exhibited metabolic depression at water temperatures forecasted to be regularly experienced by the year 2050, according to current climate projections. The impacts of climate change, coupled with habitat destruction and degradation of hydrological connectivity, make larval communities increasingly vulnerable to mass-mortality and displacement. This places ecosystem productivity and functionality at risk through cascading negative effects of recruitment limitation. Further focus on this subject will help disentangle the effects of process rates and scales of transport that underlie community assemblages in mangrove systems. Furthermore, identifying physiological bottlenecks of key taxa and habitat provisioning that enhance larval survival will be helpful to prioritize strategies for conservation management in dynamic intertidal settings.

Species are often exposed to novel thermal regimes as a result of anthropogenic activities. Understanding the extent to which populations are locally adapted to the thermal regime may allow us to better predict the response of organisms to novel thermal conditions. We collected virile crayfish, Faxonius virilis, from eight populations along a latitudinal gradient and measured their routine metabolic rates (RMR) and thermal tolerance. Countergradient variation suggests that organisms from northern latitudes may spend more energy foraging as an adaptation to the shorter growing season. Thus, we hypothesized that crayfish RMR would be positively related to latitude. We also expected high latitude populations to have a greater sensitivity to acute temperature change and a lower thermal tolerance. In support of our hypothesis, there was a significant positive relationship between latitude and crayfish RMR at night when crayfish are most active, and crayfish from high latitude populations were more thermally sensitive. Thus, changes in the thermal regime are likely to alter the activity level of this species, which could alter its ecological impacts. In addition, virile crayfish across the latitudinal gradient had a high thermal tolerance, which may contribute to the success of this species in novel environments.

Temperature is one of the most important factors governing the activity of ectothermic species, and it plays an important but less studied role in the manifestation of invasive species impacts. In this study, we investigated temperature-specific feeding and metabolic rates of invasive and native crayfish, and evaluated how temperature regulates their ecological impacts at present and in future according to different climatic scenarios by bioenergetics modelling. We conducted a series of maximum food consumption experiments and measured the metabolic rates of cold-adapted native noble crayfish (Astacus astacus) and invasive signal crayfish (Pacifastacus leniusculus) originally from a warmer environment over a temperature gradient resembling natural temperatures in Finland. The maximum feeding rates and routine metabolic rates (RMR) of native noble crayfish were significantly higher at low temperatures (< 10 °C than the rates of invasive signal crayfish. The RMRs of the species crossed at 18 °C, and the RMRs of signal crayfish were higher at temperatures above 18 °C. These findings indicate that the invader’s thermal niche has remained stable, and the potential impacts per capita are lower at suboptimal cold temperatures than for the native species. Our bioenergetics modelling showed that the direct annual predation impact of noble and signal crayfish seem similar, although the seasonal dynamics of the predation differs considerably between species. Our results highlight that the temperature-specific metabolic and feeding rates of species need to be taken into account in the impact assessment instead of simple generalisations of the direction or magnitude of impacts.

Taurine is a non-proteinogenic sulfonic acid found in high concentrations inside vertebrate cardiomyocytes and its movement across the sarcolemmal membrane is critical for cell volume regulation. Taurine deficiency is rare in mammals, where it impairs cardiac contractility and leads to congestive heart failure. In fish, cardiac taurine levels vary substantially between species and can decrease by up to 60% in response to environmental change but its contribution to cardiac function is understudied. We addressed this gap in knowledge by generating a taurine-deficient rainbow trout (Oncorhynchus mykiss) model using a feed enriched with 3% β-alanine to inhibit cellular taurine uptake. Cardiac taurine was reduced by 17% after 4 weeks with no effect on growth or condition factor. Taurine deficiency did not affect routine or maximum rates of O2 consumption, aerobic scope, or critical swimming speed in whole animals but cardiac contractility was significantly impaired. In isometrically contracting ventricular strip preparations, the force–frequency and extracellular Ca2+-sensitivity relationships were both shifted downward and maximum pacing frequency was significantly lower in β-alanine fed trout. Cardiac taurine deficiency reduces sarcoplasmic reticular Ca2+-ATPase activity in mammals and our results are consistent with such an effect in rainbow trout. Our data indicate that intracellular taurine contributes to the regulation of cardiac contractility in rainbow trout. Aerobic performance was unaffected in β-alanine-fed animals, but further study is needed to determine if more significant natural reductions in taurine may constrain performance under certain environmental conditions.

For marine animals with biphasic life stages, different environmental conditions are experienced during ontogeny so that physiological constraints on early stages could explain adult distributions and life history traits. The invasive and cool-temperate adapted Mytilus galloprovincialis intertidal mussel approaches the eastern limit of its biogeographic distribution on the south coast of South Africa, where it shares a habitat with the warm-temperate adapted and indigenous Perna perna mussel. As adults, the two species exhibit different metabolic regulation capacities in response to temperature. We compared the acute metabolic response to temperature between species during the post-settlement recruit stage. Aerobic respiration rates of recently settled recruits were measured monthly for 5 months for temperatures 5 °C above or below the ambient field seawater temperature at the time of collection. Unlike adults, the capacity for aerobic metabolic regulation in response to temperature differed little between species under the conditions tested, indicating a similar degree of phenotypic or developmental plasticity in response to the thermal environment. In addition, monthly variations in metabolic patterns indicate unexpectedly high plasticity in response to recent seasonal thermal history for both species.

Significance Plastic individuals can buffer environmental changes, maintaining a stable performance across gradients. Plasticity is therefore thought to be particularly beneficial for the survival of wild populations that experience large environmental fluctuations, such as diel and seasonal temperature changes. Maintaining plasticity is widely assumed to be costly; however, empirical evidence demonstrating this cost is scarce. Here, we predict that if plasticity is costly, it would be readily lost in a stable environment, such as a laboratory. To test this, we measured a diverse range of phenotypic traits, spanning gene expression, physiology, and behavior, in wild and laboratory zebrafish acclimated to 15 temperatures. We show that laboratory fish have lost plasticity in many traits, demonstrating that maintaining plasticity carries a cost. Plasticity can allow organisms to maintain consistent performance across a wide range of environmental conditions. However, it remains largely unknown how costly plasticity is and whether a trade-off exists between plasticity and performance under optimal conditions. Biological rates generally increase with temperature, and to counter that effect, fish use physiological plasticity to adjust their biochemical and physiological functions. Zebrafish in the wild encounter large daily and seasonal temperature fluctuations, suggesting they should display high physiological plasticity. Conversely, laboratory zebrafish have been at optimal temperatures with low thermal fluctuations for over 150 generations. We treated this domestication as an evolution experiment and asked whether this has reduced the physiological plasticity of laboratory fish compared to their wild counterparts. We measured a diverse range of phenotypic traits, from gene expression through physiology to behavior, in wild and laboratory zebrafish acclimated to 15 temperatures from 10 °C to 38 °C. We show that adaptation to the laboratory environment has had major effects on all levels of biology. Laboratory fish show reduced plasticity and are thus less able to counter the direct effects of temperature on key traits like metabolic rates and thermal tolerance, and this difference is detectable down to gene expression level. Rapid selection for faster growth in stable laboratory environments appears to have carried with it a trade-off against physiological plasticity in captive zebrafish compared with their wild counterparts.

Collecting animals from the field and bringing them into the laboratory elicits acute and chronic stress responses that may affect the interpretation of experimental outcomes. The effects of prolonged laboratory holding (three months) on labile traits (metabolic rate and spontaneous activity) were quantified for the Atlantic rock crab Cancer irroratusSay, 1817. The effects of diet (heterogenous versus homogenous) on crab condition (hemolymph protein density, crab mass, and chelal compression strength) were also assessed. When offered a heterogeneous diet C. irroratus displayed a clear preference for mussels and an aversion to herring and algae. The amount crabs ate in the laboratory was negatively correlated to the density of hemolymph protein at the time of collection, which affirms the strong link between nutritional status and hemolymph protein in crustaceans. It also suggests that crabs in good nutritional condition may forgo eating even a high-quality meal if they are stressed. Overall, providing a heterogenous diet did not significantly improve survival rates or affect labile-trait responses in crabs. In contrast, prolonged holding in the laboratory had considerable effects on labile traits: resting metabolic rate (RMR) was highest after one week, but declined over the holding period. There was also a reduction in variation of locomotor activity for approximately 4 weeks. Acute stress responses (increased RMR and activity) also occurred after transfer from holding tanks to experimental chambers, likely due to animal handling. Given the increasing attention paid to animal sentience and welfare, especially for decapod crustaceans, the amount of time that wild crustaceans are held in the laboratory should be considered carefully.

Carryover effects of environmental stressors occur when experiences of the environment in earlier life stages or seasons influence the performance of individuals later in life. These can be especially critical for species that have diverse developmental transition periods in their life cycle, such as salmonid fish. Sublethal changes in metabolism, size, or growth experienced in early life stages may have a long‐lasting effect on the subsequent life performance of these species, but very few studies have formally tested these changes in relation to environmental stressors. Here, we investigated whether different types of fine sediment result in carryover effects that change the life performance of migratory brown trout. First, we manipulated the early habitat conditions of brown trout through the life stages from egg to fry by incubating them in varying substrate treatments (i.e., gravel without added sediment, gravel with added fine sand, and gravel with added organic matter). Exposure to fine sediment during early development had serious effects on the metabolism, size, escape responses, timing of emergence, and potential survival of early life stages. These carryover effects were persistent and remained present over the critical life shift from relying on parentally provided resources as immobile eggs to independent exogenous feeding as parr. Second, fish were relocated as parr to either their original or different treatment environments and their metabolism, size, and growth were reanalyzed. The effects of environmental stress were observed later in their life cycle when fry from the gravel treatment were relocated to sand or organic‐rich treatments. These were found to be significantly smaller in size and had a higher metabolic rate than fry maintained in their original treatment environment. Together, our study experimentally demonstrated that the carryover effects of environmental stressors experienced in early stages may influence the fitness outcomes of migratory fish later in life. We suggest that sublethal environmental stressors should be better considered in restoration schemes and management strategies to reverse the current trend of declining salmonid populations.

Under the background of climate change, increasing attention has focused on the effects of ocean deoxygenation on marine organisms. However, few studies address the effects of different food deprivation states on hypoxia tolerance. We therefore investigated the metabolic responses of the Atlantic rock crab, Cancer irroratus (starved 28–35 days, fasted 3–5 days and recently fed). Starved-crab exhibited the lowest critical oxygen saturation (Scrit), while fed-crab had the highest Scrit. The fed-crab maintained an elevated postprandial oxygen consumption (MO2) even below the Scrit of fasted-crab indicating reserved aerobic scopes for critical activities in severe hypoxia. Following feeding, hypoxia (50% and 20% oxygen saturation, SO2) retarded the specific dynamic action resulting in lower peak MO2 and longer duration. The starved-crab exhibited a lower peak MO2, prolonged duration and higher energy expenditure than fasted-crab after feeding. The decline in arterial PO2 was most pronounced below the Scrit for both fasted- and starved-crab. The higher hemocyanin concentration ([Hc]) of fasted-crab (than starved-crab) suggested they had improved oxygen transport capacity, but hypoxia did not increase [Hc] during the 72-h experiment. Following feeding, the fasted-crab significantly increased l-lactate concentration ([l-lactate]) in 20% SO2, which was not observed in starved-crab. These results suggest starvation may trigger a cross-tolerance to hypoxia. Because crabs can undergo long periods of food deprivation in their natural environment, future studies should consider how this may affect their ability to deal with environmental perturbations.

Offshore migration of Pacific salmon Oncorhynchus spp. is partly triggered by increasing body size and high motility in the early stages of life. The survival of juvenile salmon may depend on their growth rate during the first few months in the sea, and this factor partly regulates the dynamics of adult populations. Here, we assessed the effects of water temperature and food availability on the growth of juvenile chum salmon O. keta. In addition, by combining the measurements of metabolic performance for growth and activity (Absolute Aerobic Scope: AAS) with a bioenergetics model, we estimated the energy allocation for different activities in the juveniles. Under high temperatures (14 °C), juveniles reared at low food levels (1% body weight) allocated less than half their energy for growth than those reared at high food levels (4% body weight). These findings suggest that high temperature and low food level constrain the growth of juveniles, providing an insight into the effect of the recent increase in warm and low-nutrient water masses on survival of juveniles and catches of adult chum salmon on the Pacific side of Honshu Island, Japan.

The effect of salinity on oxygen consumption rate and hemolymph osmolarity of the palaemonid prawn Macrobrachium tenellum (Smith, 1871) maintained at 0, 5, 10, 15, 20 and 25 psu was analyzed. Oxygen consumption rate was measured in respiratory chambers and osmolality from samples of hemolymph. Oxygen consumption rose significantly beyond 15 psu, with individuals showing hyper regulatory behavior from 0 to 10 psu, being able to maintain its internal solutes concentration (426–504 mmol kg–1) higher than that of the water (153–348 mmol kg–1). They acted as hypo-regulators from 15 to 25 psu as their internal solute concentration (454–562 mmol kg–1) was lower than that of the water (459–744 mmol kg–1). The isosmotic point was 505 mmol kg–1 at 16 psu, and survival was high in all salinities. The osmotic behavior of M. tenellum allows it to successfully invade fresh water by keeping constant the ionic and osmotic concentrations of both extra- and intra-cellular solute concentrations, always above fresh water, but varying its O2 consumption as salinity changes. The implications of such adaptations for the dispersal of the species into freshwater habitats is discussed.

Sportfishing and hatchery practices routinely subject fish to acute temperature changes through placement of fish in live wells and normal handling and transportation procedures. Acute temperature changes alter metabolic rate in ectotherms; however, the rapidity of the response to reach a new homeostatic state is not well known. Therefore, the response duration in metabolic rate after acute temperature change was measured in two centrarchid species, the Largemouth Bass Micropterus salmoides and Redear Sunfish Lepomis microlophus, which are representative of two different body shapes and are both commonly pursued in recreational fishing and reared in hatcheries. Largemouth Bass were acclimated to either 20°C or 30°C, and Redear Sunfish were acclimated to 24°C. Aerobic metabolic rate was measured immediately after acute temperature change (−4, +0, or +4°C) and was measured repeatedly in cycles of 5.5 or 10.0 min, respectively, until the metabolic rate stabilized. In Largemouth Bass, the metabolic rate stabilized similarly or more slowly following a moderate high-temperature shock (+4°C; 44 min) compared to transfer to conditions with no temperature change (+0°C) or a moderate low-temperature shock (−4°C; 16–48 min). In contrast, the metabolic rate in Redear Sunfish stabilized faster after transfer to +4°C (15 min) than after transfer to −4°C or +0°C (both 31 min), possibly because the elevated metabolic rate after transfer was sustained. Notably, for both species, metabolic rates stabilized at a generally lower level after transfer to −4°C than after transfer to +0°C or +4°C. Therefore, the duration until stabilization of metabolic rate after acute temperature change may depend upon species and acclimation temperature, although for both species examined, the energy savings in reduced metabolic rates after moderate cold shock may be beneficial for recovery from sportfishing or hatchery practices.

Metabolic rate has long been used in animal adaptation and performance studies, and individual oxygen consumption is used as proxy of metabolic rate. Stygofauna are organisms adapted to groundwater with presumably lower metabolic rates than their surface relatives. How stygofauna will cope with global temperature increase remains unpredictable. We studied the thermal acclimation and metabolic scaling with body mass of a stygobitic crustacean, Proasellus lusitanicus, in the climate change scenario. We measured oxygen consumption rates in a thermal ramp-up experiment over four assay temperatures and tested two hypotheses: (i) P. lusitanicus exhibits narrow thermal plasticity, inadequate for coping with a fast-increasing thermal regime; and (ii) oxygen consumption rates scale with the body mass by a factor close to 0.75, as commonly observed in other animals. Our results show that P. lusitanicus has low thermal plasticity in a fast-increasing thermal regime. Our data also suggest that oxygen consumption rates of this species do not follow mass-dependent scaling, potentially representing a new trait of metabolic optimization in groundwater habitats, which are often limited in food and oxygen. Species with limited dispersal capacities and rigid metabolic guilds face extinction risk due to climate change and omitting groundwater ecosystems from climate change agendas emphasizes the unprotected status of stygofauna.

Sexual signals produced by males play a central role in sexual selection, but the relationship between these traits and the quality of the bearer are often ambiguous. Secondary sexual traits may represent genetic quality of the bearer, resulting in positive relationships with physiological state, or may be costly to produce, showing trade-off with physiological state. A number of studies have explored the relationships between secondary sexual traits and other functional traits, but few have studied their fitness consequences. We studied the link between diverse physiological traits and both morphological and behavioural sexual traits and examined how their interplay influences offspring viability in the three-spined stickleback. Male sticklebacks showing nest building and courtship behaviour were smaller than those not investing in reproductive activities. There was no evidence that the expression of red nuptial colouration and the quality of courtship behaviour of males are positively related to their metabolic rates, swim ability, oxidative damage and mtDNA copy number. However, individuals showing larger red nuptial colour areas had higher levels of oxidative DNA damage in their sperm. Male courtship behaviour and aggressiveness, but not red colour area, were good predictors of offspring hatching and survival. Our results suggest that, in our study population at the southern edge of the species’ distribution, sexual colouration of male sticklebacks was not a good indicator of their body state, but both courtship quality and aggressiveness during the courtship are reliable cues of their gamete quality, influencing the viability of their offspring. Thus, females that choose mates based on their courtship behaviour will have high fitness. In the study population, which represents a fast pace-of-life with high reproductive rate and short lifespan, sexual ornaments of males may not honestly signal their physiological and physical state because they invest at maximum in a single reproductive season despite high costs.

Herein, we aimed to establish an aerobic exercise-induced physiological myocardial hypertrophy zebrafish (Danio rerio) model and to explore the underlying molecular mechanism. After 4 weeks of aerobic exercise, the AMR and Ucrit of the zebrafish increased and the hearts were enlarged, with thickened myocardium, an increased number of myofilament attachment points in the Z-line, and increased compaction of mitochondrial cristae. We also found that the mTOR signaling pathway, angiogenesis, mitochondrial fusion, and fission event, and mitochondrial autophagy were associated with the adaptive changes in the heart during training. In addition, the increased mRNA expression of genes related to fatty acid oxidation and antioxidation suggested that the switch of energy metabolism and the maintenance of mitochondrial homeostasis induced cardiac physiological changes. Therefore, the zebrafish heart physiological hypertrophy model constructed in this study can be helpful in investigating the cardioprotective mechanisms in response to aerobic exercise.

Fish that strike angling lures often have a set of characteristics that predispose them to capture. Vulnerable fish may then be removed from a population, either through harvest or incidental mortality, and in turn leave individuals in a population that are less vulnerable to angling. Over time, the removal of vulnerable individuals can erode capture rates, possibly resulting in evolutionary changes if traits that result in capture correlate with characteristics such as fecundity or growth. We sought to define the mechanisms driving individual angling vulnerability in Muskellunge Esox masquinongy, with the intent of informing management activities to conserve populations. The behavior of individually identified Muskellunge (n = 68; mean TL = 310.2 mm; range = 229–350 mm) was assessed using standard open-field tests; the fish were then stocked into earthen-bottom ponds to assess angling vulnerability. After angling, all captured fish and a subset of uncaptured fish were assessed for metabolic parameters. Results indicated that larger Muskellunge displaying low levels of exploration and aggression were preferentially captured. Behaviors such as boldness and activity did not influence capture, and metabolic parameters did not differ between captured and uncaptured fish.

A series of crosses identify standing genetic variation for thermal sensitivity of respiration and protein synthesis among larval families within a species, conferring physiological resilience to environmental change.

The metabolic rate (ṀO2) of eurythermal fishes changes in response to temperature, yet it is unclear how changes in mitochondrial function contribute to changes in ṀO2. We hypothesized that ṀO2 would increase with acclimation temperature in the threespine stickleback (Gasterosteus aculeatus) in parallel with metabolic remodeling at the cellular level but that changes in metabolism in some tissues, such as liver, would contribute more to changes in ṀO2 than others. Threespine stickleback were acclimated to 5, 12 and 20°C for 7 to 21 weeks. At each temperature, standard and maximum metabolic rate (SMR and MMR, respectively), and absolute aerobic scope (AAS) were quantified, along with mitochondrial respiration rates in liver, oxidative skeletal and cardiac muscles, and the maximal activity of citrate synthase (CS) and lactate dehydrogenase (LDH) in liver, and oxidative and glycolytic skeletal muscles. SMR, MMR and AAS increased with acclimation temperature, along with rates of mitochondrial phosphorylating respiration in all tissues. Low SMR and MMR at 5°C were associated with low or undetectable rates of mitochondrial complex II activity and a greater reliance on complex I activity in liver, oxidative skeletal muscle and heart. SMR was positively correlated with cytochrome c oxidase (CCO) activity in liver and oxidative muscle, but not mitochondrial proton leak, whereas MMR was positively correlated with CCO activity in liver. Overall, the results suggest that changes in ṀO2 in response to temperature are driven by changes in some aspects of mitochondrial function in some, but not all, tissues of threespine stickleback.

Excessive alcohol consumption can cause alcoholic myopathy, but the molecular mechanism is still unclear. In this study, zebrafish were exposed to 0.5% alcohol for eight weeks to investigate the effect of alcohol on skeletal muscle and its molecular mechanism. The results showed that the body length, body weight, cross-sectional area of the skeletal muscle fibers, Ucrit, and MO2max of the zebrafish were significantly decreased after alcohol exposure. The expression of markers of skeletal muscle atrophy and autophagy was increased, and the expression of P62 was significantly reduced. The content of ROS, the mRNA expression of sod1 and sod2, and the protein expression of Nox2 were significantly increased. In addition, we found that the inflammatory factors Il1β and Tnfα were significantly enriched in skeletal muscle, and the expression of the HMGB1/TLR4/NF-κB signaling axis was also significantly increased. In summary, in this study, we established a zebrafish model of alcohol-induced skeletal muscle atrophy and further elucidated its pathogenesis.

Many fishes use their tail as the main thrust producer during swimming. This fin's diversity in shape and size influences its physical interactions with water as well as its ecological functions. Two distinct tail morphologies are common in bony fishes: flat, truncate tails which are best suited for fast accelerations via drag forces, and forked tails that promote economical, fast cruising by generating lift-based thrust. This assumption is based primarily on studies of the lunate caudal fin of Scombrids (i.e. tuna, mackerel), which is comparatively stiff and exhibits an airfoil-type cross-section. However, this is not representative of the more commonly observed and taxonomically widespread flexible forked tail, yet similar assumptions about economical cruising are widely accepted. Here, we present the first comparative experimental study of forked versus truncate tail shape and compare the fluid mechanical properties and energetics of two common nearshore fish species. We examined the hypothesis that forked tails provide a hydrodynamic advantage over truncate tails at typical cruising speeds. Using experimentally derived pressure fields, we show that the forked tail produces thrust via acceleration reaction forces like the truncate tail during cruising but at increased energetic costs. This reduced efficiency corresponds to differences in the performance of the two tail geometries and body kinematics to maintain similar overall thrust outputs. Our results offer insights into the benefits and tradeoffs of two common fish tail morphologies and shed light on the functional morphology of fish swimming to guide the development of bio-inspired underwater technologies.

European sea bass is a species of great commercial value for fisheries and aquaculture. Rising temperatures may jeopardize the performance and survival of the species across its distribution and farming range, making the investigation of its thermal responses highly relevant. In this article, the metabolic scope, performance, and tolerance of juvenile E. sea bass reared under three high water temperatures (24, 28, 33°C), for a period of three months was evaluated via analysis of selected growth performance and physiological indicators. Effects on molecular, hormonal, and biochemical variables were analyzed along with effects of acclimation temperature on the metabolic rate and Critical Thermal maximum (CTmax). Despite signs of thermal stress at 28°C indicated by high plasma cortisol and lactate levels as well as the upregulation of genes coding for Heat Shock Proteins (HSP), E. sea bass can maintain high performance at that temperature which is encouraging for the species culture in the context of a warming ocean. Critical survivability thresholds appear sharply close to 33°C, where the aerobic capacity declines and the overall performance diminishes. European sea bass demonstrates appreciable capacity to cope with acute thermal stress exhibiting CTmax as high as 40°C for fish acclimated at high temperatures, which may indicate resilience to future heatwaves events.

The shared-pathway hypothesis offers a cellular explanation for the connection between ketocarotenoid pigmentation and individual quality. Under this hypothesis, ketocarotenoid metabolism shares cellular pathways with mitochondrial oxidative phosphorylation such that red carotenoid-based coloration is inextricably linked mitochondrial function. To test this hypothesis, we exposed Tigriopus californicus copepods to a mitochondrially targeted protonophore, 2,4-dinitrophenol (DNP), to induce proton leak in the inner mitochondrial membranes. We then measured whole-animal metabolic rate and ketocarotenoid accumulation. As observed in prior studies of vertebrates, we observed that DNP treatment of copepods significantly increased respiration and that DNP-treated copepods accumulated more ketocarotenoid than control animals. Moreover, we observed a relationship between ketocarotenoid concentration and metabolic rate, and this association was strongest in DNP-treated copepods. These data support the hypothesis that ketocarotenoid and mitochondrial metabolism are biochemically intertwined. Moreover, these results corroborate observations in vertebrates, perhaps suggesting a fundamental connection between ketocarotenoid pigmentation and mitochondrial function that should be explored further.

This study assessed the energy budget for juvenile Atlantic Sea Scallop, Placopecten magellanicus, during a natural drop in temperature (15.6°C to 5.8°C) over an 8-week time period during the fall at three different enrichment levels of carbon dioxide (CO2). Every 2 weeks, individuals were sampled for ecophysiological measurements of feeding activity, respiration rate (RR) and excretion rate (ER) to enable the calculation of scope for growth (SFG) and atomic oxygen:nitrogen ratios (O:N). In addition, 36 individuals per treatment were removed for shell height, dry tissue weight (DTW) and dry shell weight (DSW). We found a significant decrease in feeding rates as CO2 increased. Those rates also were significantly affected by temperature, with highest feeding at 9.4°C. No significant CO2 effect was observed for catabolic energy processes (RR and ER); however, these rates did increase significantly with temperature. The O:N ratio was not significantly affected by CO2, but was significantly affected by temperature. There was a significant interaction between CO2 and temperature for ER and the O:N ratio, with low CO2 levels resulting in a U-shaped response that was not sustained as CO2 levels increased. This suggests that the independent effects of CO2 and temperature observed at low levels are different once a CO2 threshold is reached. Additionally, there were significant differences in growth estimators (shell height and DSW), with the best growth occurring at the lowest CO2 level. In contrast to temperature variations that induced a trade-off response in energy acquisition and expenditure, results from this research support the hypothesis that sea scallops have a limited ability to alter physiological processes to compensate for increasing CO2.

The hypoxic ventilatory response (HVR) in fish is an important reflex that aids O2 uptake when low environmental O2 levels constrain diffusion. In developing zebrafish (Danio rerio), the acute HVR is multiphasic, consisting of a rapid increase in ventilation frequency (fV) during hypoxia onset, followed by a decline to a stable plateau phase above fV under normoxic conditions. In this study, we examined the potential role of catecholamines in contributing to each of these phases of the dynamic HVR in zebrafish larvae. We showed that adrenaline elicits a dose-dependent β-adrenoreceptor (AR)-mediated increase in fV that does not require expression of β1-ARs, as the hyperventilatory response to β-AR stimulation was unaltered in adrb1−/− mutants, generated by CRISPR/Cas9 knockout. In response to hypoxia and propranolol co-treatment, the magnitude of the rapidly occurring peak increase in fV during hypoxia onset was attenuated (112±14 breaths min−1 without propranolol to 68±17 breaths min−1 with propranolol), whereas the increased fV during the stable phase of the HVR was prevented in both wild type and adrb1−/− mutants. Thus, β1-AR is not required for the HVR and other β-ARs, although not required for initiation of the HVR, are involved in setting the maximal increase in fV and in maintaining hyperventilation during continued hypoxia. This adrenergic modulation of the HVR may arise from centrally released catecholamines because adrenaline exposure failed to activate (based on intracellular Ca2+ levels) cranial nerves IX and X, which transmit O2 signals from the pharyngeal arch to the central nervous system.

Juvenile fall-run Chinook salmon (Oncorhynchus tshawytscha) in the Sacramento–San Joaquin River Basin experience temporally and spatially heterogenous temperature regimes, between cool upper tributaries and the warm channelized Delta, during freshwater rearing and outmigration. Limited water resources necessitate human management of dam releases, allowing temperature modifications. The objective of this study was to examine the effect of temperature on specific dynamic action (SDA), or the metabolic cost associated with feeding and digestion, which is thought to represent a substantial portion of fish energy budgets. Measuring SDA with respect to absolute aerobic scope (AAS), estimated by the difference between maximum metabolic rate (MMR) and standard metabolic rate (SMR), provides a snapshot of its respective energy allocation. Fish were acclimated to 16°C, raised or lowered to each acute temperature (13°C, 16°C, 19°C, 22°C or 24°C), then fed a meal of commercial pellets weighing 2% of their wet mass. We detected a significant positive effect of temperature on SMR and MMR, but not on AAS. As expected, there was no significant effect of temperature on the total O2 cost of digestion, but unlike other studies, we did not see a significant difference in duration, peak metabolic rate standardized to SMR, time to peak, percent of meal energy utilized, nor the ratio of peak O2 consumption to SMR. Peak O2 consumption represented 10.4–14.5% of AAS leaving a large amount of aerobic capacity available for other activities, and meal energy utilized for digestion ranged from 5.7% to 7.2%, leaving substantial remaining energy to potentially assimilate for growth. Our juvenile fall-run Chinook salmon exhibited thermal stability in their SDA response, which may play a role in maintaining homeostasis of digestive capability in a highly heterogeneous thermal environment where rapid growth is important for successful competition with conspecifics and for avoiding predation.

With the growing prevalence of hypoxia (O2 levels ≤2 mg l−1) in aquatic and marine ecosystems, there is increasing interest in the adaptive mechanisms fish may employ to better their performance in stressful environments. Here, we investigated the contribution of a proposed strategy for enhancing tissue O2 extraction – plasma-accessible carbonic anhydrase (CA-IV) – under hypoxia in a species of estuarine fish (red drum, Sciaenops ocellatus) that thrives in fluctuating habitats. We predicted that hypoxia-acclimated fish would increase the prevalence of CA-IV in aerobically demanding tissues to confer more efficient tissue O2 extraction. Furthermore, we predicted the phenotypic changes to tissue O2 extraction that occur with hypoxia acclimation may improve respiratory and swim performance under 100% O2 conditions (i.e. normoxia) when compared with performance in fish that have not been acclimated to hypoxia. Interestingly, there were no significant differences in relative CA-IV mRNA expression, protein abundance or enzyme activity between the two treatments, suggesting CA-IV function is maintained under hypoxia. Likewise, respiratory performance of hypoxia-acclimated fish was similar to that of control fish when tested in normoxia. Critical swim speed (Ucrit) was significantly higher in hypoxia-acclimated fish but translated to marginal ecological benefits with an increase of ∼0.3 body lengths per second. Instead, hypoxia-acclimated fish may have relied more heavily on anaerobic metabolism during their swim trials, utilizing burst swimming 1.5 times longer than control fish. While the maintenance of CA-IV may still be an important contributor for hypoxia tolerance, our evidence suggests hypoxia-acclimated red drum are using other mechanisms to cope in an O2-depleted environment.

Nile tilapia (Oreochromis niloticus) is one of the most important food fishes in global aquaculture. The optimal rearing temperature for Nile tilapia is 27–30 °C; however, in some Asian breeding areas, such as south China, water temperatures in summer frequently exceed 35 °C for several days. Potential effects of long-term exposure to high temperatures on the survival and metabolism of tilapia are unclear. In this study, genetically improved farmed tilapia, age six weeks, were exposed to water temperatures of 28, 32, and 36 °C for 15 weeks. Mean survival rates and tolerance to hypoxia were significantly reduced, and respiratory rates were increased in fish reared at 36 °C, compared to the 28 and 32 °C treatments (p

Plasma serotonin (5-hydroxytryptamine, 5-HT) homeostasis is maintained through the combined processes of uptake (via the 5-HT transporter SERT, and others), degradation (via monoamine oxidase, MAO) and excretion. Previous studies have shown that inhibiting SERT, which would inhibit 5-HT uptake and degradation, attenuates parts of the cardiovascular hypoxia reflex in gulf toadfish (Opsanus beta), suggesting that these 5-HT clearance processes may be important during hypoxia exposure. Therefore, the goal of this experiment was to determine the effects of mild hypoxia on 5-HT uptake and degradation in the peripheral tissues of toadfish. We hypothesized that 5-HT uptake and degradation would be upregulated during hypoxia, resulting in lower plasma 5-HT, with uptake occurring in the gill, heart, liver and kidney. Fish were exposed to normoxia (97.6% O2 saturation, 155.6 Torr) or 2 min, 40 min or 24 h mild hypoxia (50% O2 saturation, ∼80 Torr), then injected with radiolabeled [3H]5-HT before blood, urine, bile and tissues were sampled. Plasma 5-HT levels were reduced by 40% after 40 min of hypoxia exposure and persisted through 24 h. 5-HT uptake by the gill was upregulated following 2 min of hypoxia exposure, and degradation in the gill was upregulated at 40 min and 24 h. Interestingly, there was no change in 5-HT uptake by the heart and degradation in the heart decreased by 58% within 2 min of hypoxia exposure and by 85% at 24 h. These results suggest that 5-HT clearance is upregulated during hypoxia and is likely driven, in part, by mechanisms within the gill and not the heart.

The excessive worldwide production of plastic materials results in omnipresent microplastic pollution. Scientific studies dealing with the impacts of microplastics on aquatic ecosystems focus mainly on the marine environment, documenting the effect on the functional traits of various organisms. Polystyrene, one of the most commonly used plastics, has become a widely used model in this respect. In our study, freshwater shrimps (Neocardina heteropoda) were exposed to virgin polystyrene particles (size 0.5 mm; nominal concentration 8 mgL−1), and their behavioral and physiological responses were compared to control shrimp. The exposed shrimps exhibited modified activity patterns (greater speeds, accelerations and distances moved), accompanied by a lowered standard metabolic rate (SMR). The observed effects differed in their progression from the 7th to 14th day of exposure, from undetectable changes (distance, SMR) to significant differences (speed, acceleration). Significant differences were also detected in the behavioral syndromes expressed by the exposed and controlled shrimps, indicating that the microplastics influence not only the particular traits, but also their functional relationships. As such, our study contributes to the integration of behavioral ecotoxicology in risk assessment, documenting the adverse performance of freshwater invertebrates exposed to microplastics with the potential to transpose the problem to higher levels of the food web.

European sea bass (Dicentrarchus labrax) is a large, economically important fish species with a long generation time whose long-term resilience to ocean acidification (OA) and warming (OW) is not clear. We incubated sea bass from Brittany (France) for two generations (>5 years in total) under ambient and predicted OA conditions (PCO2: 650 and 1700 µatm) crossed with ambient and predicted OW conditions in F1 (temperature: 15–18°C and 20–23°C) to investigate the effects of climate change on larval and juvenile growth and metabolic rate. We found that in F1, OA as a single stressor at ambient temperature did not affect larval or juvenile growth and OW increased developmental time and growth rate, but OAW decreased larval size at metamorphosis. Larval routine and juvenile standard metabolic rate were significantly lower in cold compared with warm conditioned fish and also lower in F0 compared with F1 fish. We did not find any effect of OA as a single stressor on metabolic rate. Juvenile PO2,crit was not affected by OA or OAW in both generations. We discuss the potential underlying mechanisms resulting in the resilience of F0 and F1 larvae and juveniles to OA and in the beneficial effects of OW on F1 larval growth and metabolic rate, but contrastingly in the vulnerability of F1, but not F0 larvae to OAW. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures.

Deoxygenation and warming affect adult fish physiology in all aquatic ecosystems, but how these stressors impact the energetics of sensitive developing stages is largely unknown. Addressing this knowledge gap, we investigated chronic and acute effects of two stressors (high-temperature and hypoxia) in yolk-sac larval (48-168 hpf) zebrafish (Danio rerio) energy budgets measuring, oxygen consumption rate (ṀO2), growth rate (absolute (AGR) & specific (SGR)), % net conversion efficiency (KN), net cost of growth (Cr) and scaling relationships. Embryos and larvae were raised under four chronic treatments, 1) control (28°C & pO2 21kPa, T28O21), 2) high-temperature (31°C & pO2 21kPa, T31O21), 3) hypoxia (28°C & pO2 11kPa, T28TO11), and 4) high-temperature and hypoxia (31°C & pO2 11kPa, T31O11). From each chronic treatment, larvae were acutely exposed to the same combinations of stressors for 1h in a respirometer. At hatching, larvae from chronic high-temperature (T31O21 & T31O11) treatments were larger, (higher dry mass (MD) & standard length (Ls)) than controls (T28O21 & T28O11), but by the end of the yolk-sac stage, increased metabolic demands diverted energy away from growth increasing Cr and lowering % KN. Control metabolic scaling relationships were significant (metabolic exponent b, log-log slope; 0.83±0.68±95% CI, combined b of 1.19±0.25) and differed from 0.75, but metabolic levels (La) were lower (2.11±0.90) in acute hypoxia (3.35±1.52) and high-temperature/hypoxia (2.61±1.55). Thus, high-temperature dominated larval energetics acting synergistically with hypoxia increasing cumulative energetic costs and making allostasis difficult compared to older stages.

Ocean acidification (OA) resulting from anthropogenic CO2 emissions is impairing the reproduction of marine organisms. While parental exposure to OA can protect offspring via carryover effects, this phenomenon is poorly understood in many marine invertebrate taxa. Here, we examined how parental exposure to acidified (pH 7.40) versus ambient (pH 7.72) seawater influenced reproduction and offspring performance across six gametogenic cycles (13 weeks) in the estuarine sea anemone Nematostella vectensis. Females exhibited reproductive plasticity under acidic conditions, releasing significantly fewer but larger eggs compared to ambient females after 4 weeks of exposure, and larger eggs in two of the four following spawning cycles despite recovering fecundity, indicating long-term acclimatization and greater investment in eggs. Males showed no changes in fecundity under acidic conditions but produced a greater percentage of sperm with high mitochondrial membrane potential (MMP; a proxy for elevated motility), which corresponded with higher fertilization rates relative to ambient males. Finally, parental exposure to acidic conditions did not significantly influence offspring development rates, respiration rates, or heat tolerance. Overall, this study demonstrates that parental exposure to acidic conditions impacts gamete production and physiology but not offspring performance in N. vectensis, suggesting that increased investment in individual gametes may promote fitness.

Heatwaves are increasing in frequency and intensity under climate change. Freshwater ecosystems are among the most thermally impacted systems, within which agricultural streams are experiencing the most extreme heatwaves and deserve prioritised focus. Heatwaves are approaching the upper thermal limits of many fishes but have received little attention to date. To study whether and how fish tolerate heatwaves from a physiological perspective, we simulated single, multiple, and extended heatwaves at 32 and 34°C in the laboratory, based on high‐resolution summer temperatures recorded in agricultural versus forested streams in Illinois, U.S.A. By investigating the effects of heatwaves on 25°C acclimated fathead minnow Pimephales promelas, an important prey species across North America, we witnessed its high thermal resilience, including a rapid return to metabolic homeostasis after single and multiple heatwaves, measured by oxygen consumption rate. During an extended heatwave, fathead minnow were still able to partially lower oxygen consumption rate after the initial exposure. We also found transient increases in their critical thermal maximum, especially after higher intensity and frequency of heatwaves. However, the thermal resilience of fathead minnow did come with costs, including reduced anaerobic capacity indicated by decreased lactate dehydrogenase activity and impaired antioxidant defence indicated by reduced superoxide dismutase in white muscle. By monitoring metabolic costs and physiological adjustments of fish during and after heatwaves, we showed that fathead minnow were resilient to simulated current and near‐future heatwaves, which may allow them to cope with thermal extremes expected in agricultural streams. Overall, the real‐time monitoring of fish responses to heatwaves incorporates natural dynamics of thermal patterns. It facilitates mechanistic understandings of how fish react to thermal challenges in the real world and offers opportunities to incorporate high‐resolution metabolic costs into future bioenergetic modelling.

In the present study, oxygen consumption of two sturgeon species, beluga (Huso huso), sterlet (Acipenser ruthenus), and their hybrid reared in a recirculating aquaculture system were compared over body intervals from 54–107 g to determine the interspecific variation of metabolic rate. Metabolic rates were measured using the intermittent-flow respirometry technique. Standard oxygen consumption rates (SMR, mg O2 h−1) of sterlet were 30% higher compared with beluga and 22% higher compared with bester hybrid. The routine metabolic rate (RMR, mg O2 h−1) averaged 1.58 ± 0.13 times the SMR for A. ruthenus, 1.59 ± 0.3 for H. huso, and 1.42 ± 0.15 for the hybrid bester. However, the study revealed no significant differences (p > 0.05) between mean values of SMR and RMR for beluga and bester hybrid. The scaling coefficient reflected a closed isometry for the hybrid (b = 0.97), while for the purebred species the coefficient of 0.8 suggests a reduction in oxygen consumption with increasing body mass. These findings may contribute to understanding the differences in growth performances and oxygen requirements of the studied species reared in intensive aquaculture system.

Many insect species harbour heritable bacterial endosymbionts. Some facultative endosymbionts provide benefits to their hosts under certain environmental conditions. Facultative endosymbionts are expected to impose additional energetic expenditures to their host, reducing host fitness. While there is accumulating evidence in plant sucking insects that facultative endosymbionts reduce the fitness of their host under permissive conditions, no direct energy costs associated with facultative endosymbionts have been identified. Using the standard metabolic rate (SMR) as a measure of the energy cost of self-maintenance, we investigated whether two common facultative endosymbionts Hamiltonella defensa or Regiella insecticola increase the maintenance cost of the pea aphid Acyrthosiphon pisum which could translate into host fitness reduction ('compensation hypothesis'). In addition, we tested if there was a link between SMR and the aphid fitness and whether it depended on endosymbiont density and aphid energetic reserves. Finally, we measured SMR at different temperatures to assess the impact of suboptimal thermal conditions on physiological cost of endosymbionts. In the presence of facultative endosymbionts, aphids expressed generally a lower fitness and a higher SMR compared to uninfected ones, in accordance with the 'compensation hypothesis'. However, the SMR difference between infected and uninfected aphids tended to decrease with increasing temperature. Complex host genotype-by-symbiont genotype-by-temperature interactions on SMR were also revealed. Energetic budget of adult aphids appeared weakly influenced by the aphid genotype and endosymbiont species, suggesting that facultative endosymbionts primarily impact the consumption of energy resources rather than their acquisition. Density of facultative endosymbionts varied largely among aphid lines but was not associated with the fitness nor metabolic rate of aphids. This work supports the energy basis of facultative endosymbiont associated fitness costs and raises new questions about the effect of facultative endosymbionts on the energy metabolism of their host.

p-Toluene sulfonamide (p-TSA), a small molecular drug with antineoplastic activity is widely gaining interest from researchers because of its pharmacological activities. In this study, we explored the potential cardio and neural toxicity of p-TSA in sublethal concentrations by using zebrafish as an in vivo animal model. Based on the acute toxicity assay, the 96hr LC50 was estimated as 204.3 ppm, suggesting the overall toxicity of p-TSA is relatively low in zebrafish larvae. For the cardiotoxicity test, we found that p-TSA caused only a minor alteration in treated larvae after no overall significant alterations were observed in cardiac rhythm and cardiac physiology parameters, as supported by the results from expression level measurements of several cardiac development marker genes. On the other hand, we found that acute p-TSA exposure significantly increased the larval locomotion activity during the photomotor test while prolonged exposure (4 days) reduced the locomotor startle reflex activities in zebrafish. In addition, a higher respiratory rate and blood flow velocity was also observed in the acutely treated fish groups compared to the untreated group. Finally, by molecular docking, we found that p-TSA has a moderate binding affinity to skeletal muscle myosin II subfragment 1 (S1), ATPase activity, actin- and Ca2+-stimulated myosin S1 ATPase, and v-type proton ATPase. These binding interactions between p-TSA and proteins offer insights into the potential molecular mechanism of action of p-TSA on observed altered responses toward photo and vibration stimuli and minor altered vascular performance in the zebrafish larvae.

Competition and metabolism should be linked. Intraspecific variation in metabolic rates and, hence, resource demands covary with competitive ability. The effects of metabolism on conspecific interactions, however, have mostly been studied under laboratory conditions. We used a trait‐specific response‐surface design to test for the effects of metabolism on pairwise interactions of the marine colonial invertebrate, Bugula neritina in the field. Specifically, we compared the performance (survival, growth, and reproduction) of focal individuals, both in the presence and absence of a neighbor colony, both of which had their metabolic phenotype characterized. Survival of focal colonies depended on the metabolic phenotype of the neighboring individual, and on the combination of both the focal and neighbor colony metabolic phenotypes that were present. Surprisingly, we found pervasive effects of neighbor metabolic phenotypes on focal colony growth and reproduction, although the sign and strength of these effects showed strong microenvironmental variability. Overall, we find that the metabolic phenotype changes the strength of competitive interactions, but these effects are highly contingent on local conditions. We suggest future studies explore how variation in metabolic rate affects organisms beyond the focal organism alone, particularly under field conditions.

As coral reefs face warming oceans and increased coral bleaching, a whitening of the coral due to loss of microalgal endosymbionts, the possibility of evolutionary rescue offers some hope for reef persistence. In tightly linked mutualisms, evolutionary rescue may occur through evolution of one or both partners. Many obligate mutualisms are composed of relatively small, fast-growing symbionts with greater potential to evolve on ecologically relevant time scales than their relatively large, slower growing hosts. We examined the potential for adaptation of the upside-down sea jelly Cassiopea xamachana to increased temperature via evolution of its microalgal endosymbiont, Symbiodinium microadriaticum. We quantified trait variation among five algal genotypes in response to three temperatures and fitness of hosts infected with each genotype. All genotypes had positive growth rates at each temperature, but rates of respiration and photosynthesis decreased with increasing temperature. Responses varied among genotypes but were unrelated to genetic similarity. The effect of temperature on asexual reproduction and the timing of development in the host also depended on the genotype of the symbiont. Natural selection could favor different algal genotypes at different temperatures, affecting host fitness. This eco-evolutionary interaction may be a critical component of understanding species resilience in increasingly stressful environments.

The peroxisome proliferator-activated receptor γ coactivator 1 α (PGC-1α) is central to the regulation of cellular and mitochondrial energy homeostasis in mammals, but its role in other vertebrates remains unclear. Indeed, previous work suggests extensive structural and functional divergence of PGC-1α in teleosts but this remains to be directly tested. Here, we describe the initial characterization of heterozygous PGC-1α mutant zebrafish lines created by CRISPR-Cas9 disruptions of an evolutionarily conserved regulatory region of the PGC-1α proximal promoter. Using qPCR, we confirmed the disruption of PGC-1α gene expression in striated muscle, leading to a simultaneous fourfold increase in mixed skeletal muscle PGC-1α mRNA levels and an opposite fourfold downregulation in cardiac muscle. In mixed skeletal muscle, most downstream effector genes were largely unaffected yet two mitochondrial lipid transporters, carnitine palmitoyltransferase-1 and -2, were strongly induced. Conversely, PGC-1α depression in cardiac muscle reduced the expression of several transcriptional regulators (estrogen-related receptor α, nuclear respiratory factor 1, and PGC-1β) without altering metabolic gene expression. Using high-resolution respirometry, we determined that white muscle exhibited increased lipid oxidative capacity with little difference in markers of mitochondrial abundance. Finally, using whole animal intermittent respirometry, we show that mutant fish exhibit a twofold higher basal metabolism than their wild-type counterparts. Altogether, this new model confirms a central but complex role for PGC-1α in mediating energy utilization in zebrafish, and we propose its use as a valuable tool to explore the intricate regulatory pathways of energy homeostasis in a popular biomedical model.

SURF1 deficiency (OMIM # 220110) causes Leigh syndrome (LS, OMIM # 256000), a mitochondrial disorder typified by stress-induced metabolic strokes, neurodevelopmental regression and progressive multisystem dysfunction. Here, we describe two novel surf1−/− zebrafish knockout models generated by CRISPR/Cas9 technology. While gross larval morphology, fertility, and survival into adulthood appeared unaffected, surf1−/− mutants manifested adult-onset ocular anomalies and decreased swimming activity, as well as classical biochemical hallmarks of human SURF1 disease, including reduced complex IV expression and enzymatic activity and increased tissue lactate. surf1−/− larvae also demonstrated oxidative stress and stressor hypersensitivity to the complex IV inhibitor, azide, which exacerbated their complex IV deficiency, reduced supercomplex formation, and induced acute neurodegeneration typical of LS including brain death, impaired neuromuscular responses, reduced swimming activity, and absent heartrate. Remarkably, prophylactic treatment of surf1−/− larvae with either cysteamine bitartrate or N-acetylcysteine, but not other antioxidants, significantly improved animal resiliency to stressor-induced brain death, swimming and neuromuscular dysfunction, and loss of heartbeat. Mechanistic analyses demonstrated cysteamine bitartrate pretreatment did not improve complex IV deficiency, ATP deficiency, or increased tissue lactate but did reduce oxidative stress and restore glutathione balance in surf1−/− animals. Overall, two novel surf1−/− zebrafish models recapitulate the gross neurodegenerative and biochemical hallmarks of LS, including azide stressor hypersensitivity that was associated with glutathione deficiency and ameliorated by cysteamine bitartrate or N-acetylcysteine therapy.

The speckled peacock bass Cichla temensis is a popular sport and food fish that generates substantial angling tourism and utilitarian harvest within its range. Its popularity and value make this species important for management and a potential aquaculture candidate for both fisheries enhancement and food fish production. However, little is known of optimal physiochemical conditions in natural habitats, which also are important for the development of hatchery protocols for handling, spawning and grow‐out. Speckled peacock bass have been documented to have high sensitivity to extreme temperatures, but the metabolic underpinnings have not been evaluated. In this study, the effects of temperature (25, 30 and 35°C) on the standard metabolic rate (SMR) and lower dissolved oxygen tolerance (LDOT) of juvenile speckled peacock bass (mean ± standard error total length 153 ± 2 mm and wet weight 39.09 ± 1.37 g) were evaluated using intermittent respirometers after an acclimation period of 2 weeks. Speckled peacock bass had the highest SMR at 35°C (345.56 ± 19.89 mgO 2 kg −1 h −1 ), followed by 30°C (208.16 ± 12.45 mgO 2 kg −1 h −1 ) and 25°C (144.09 ± 10.43 mgO 2 kg −1 h −1 ). Correspondingly, the Q 10, or rate of increase in aerobic metabolic rate (MO 2 ) relative to 10°C, for 30–35°C was also greater (2.76) than from 25 to 30°C (2.08). Similarly, speckled peacock bass were the most sensitive to hypoxia at the warmest temperature, with an LDOT at p O 2 of 90 mmHg (4.13 mg l −1 ) at 35°C compared to p O 2 values of 45 mmHg (2.22 mg l −1 ) and 30 mmHg (1.61 mg l −1 ) at 30 and 25°C, respectively. These results indicate that speckled peacock bass are sensitive to temperatures near 35°C, therefore we recommend managing and rearing this species at 25–30°C.

Hermit crabs (Paguroidea; Latreille 1802) offer great opportunities to study animal behaviour and physiology. However, the animals’ size and sex cannot be determined when they are inside their shell; information crucial to many experimental designs. Here, we tested the effects of the two most common procedures used to make crabs leave their shells: heating the shell apex and cracking the shell with a bench press. We compared the effects of each of the two procedures on the metabolic rate, hiding time, and duration of the recovery time relative to unmanipulated hermit crabs. The hermit crabs forced to abandon their shell through heating increased their respiratory rate shortly after the manipulation (1 h) and recovered their metabolic rate in less than 24 h, as occurs in individuals suddenly exposed to high temperatures in the upper-intertidal zone. Hermit crabs removed from their shells via cracking spent more time hiding in their new shells; this effect was evident immediately after the manipulation and lasted more than 24 h, similar to responses exhibited after a life-threatening predator attack. Both methods are expected to be stressful, harmful, or fear-inducing; however, the temperature required to force the crabs to abandon the shell is below the critical thermal maxima of most inhabitants of tropical tide pools. The wide thermal windows of intertidal crustaceans and the shorter duration of consequences of shell heating compared to cracking suggest heating to be a less harmful procedure for removing tropical hermit crabs from their shells.

Chronic elevation of circulating cortisol is known to have deleterious effects on fish, but information about the consequences of prolonged cortisol elevation on the metabolism of fish is scarce. To test the effects of chronic cortisol elevation on the aerobic performance of rainbow trout, we examined how two severities of chronically elevated plasma cortisol levels affected the oxygen uptake during rest and after exhaustive exercise using a high (HC) and a medium cortisol (MC) treatment. High cortisol doses significantly affected standard (SMR) and maximum metabolic rates (MMR) compared to control fish. In comparison, the medium cortisol treatment elevated maximum metabolic rates (MMR) but did not significantly influence SMR compared to a sham group (S) and control group (C). The medium cortisol treatment resulted in a significantly increased metabolic scope due to an elevation of MMR, an effect that was abolished in the HC group due to co-occuring elevations in SMR. The elevated SMR of the HC-treated fish could be explained by increased in vitro oxygen uptake rates (MO 2 ) of specific tissues, indicating that the raised basal metabolism was caused, in part, by an increase in oxygen demand of specific tissues. Haematological results indicated an increased reliance on anaerobic metabolic pathways in cortisol-treated fish under resting conditions.

Increasing ocean temperatures have been demonstrated to have a range of negative impacts on coral reef fishes. However, despite a wealth of studies of juvenile/adult reef fish, studies of how early developmental stages respond to ocean warming are limited. As overall population persistence is influenced by the development of early life stages, detailed studies of larval responses to ocean warming are essential. Here, in an aquaria-based study we investigate how temperatures associated with future warming and present-day marine heatwaves (+3 °C) impact the growth, metabolic rate, and transcriptome of 6 discrete developmental stages of clownfish larvae (Amphiprion ocellaris). A total of 6 clutches of larvae were assessed, with 897 larvae imaged, 262 larvae undergoing metabolic testing and 108 larvae subject to transcriptome sequencing. Our results show that larvae reared at +3 °C grow and develop significantly faster and exhibit higher metabolic rates than those in control conditions. Finally, we highlight the molecular mechanisms underpinning the response of larvae from different developmental stages to higher temperatures, with genes associated with metabolism, neurotransmission, heat stress and epigenetic reprogramming differentially expressed at +3 °C. Overall, these results indicate that clownfish development could be altered under future warming, with developmental rate, metabolic rate, and gene expression all affected. Such changes may lead to altered larval dispersal, changes in settlement time and increased energetic costs.

Climate warming is a threat of imminent concern that may exacerbate the impact of nitrate pollution on fish fitness. These stressors can individually affect the aerobic capacity and stress tolerance of fish. In combination, they may interact in unexpected ways where exposure to one stressor may heighten or reduce the resilience to another stressor and their interactive effects may not be uniform across species. Here, we examined how nitrate pollution under a warming scenario affects the aerobic scope (AS), and the hypoxia and heat stress susceptibility of a generally tolerant fish species, common carp Cyprinus carpio. We used a 3 × 2 factorial design, where fish were exposed to one of three ecologically relevant levels of nitrate (0, 50, or 200 mg NO 3 - L -1 ) and one of two temperatures (18 °C or 26 °C) for 5 weeks. Warm acclimation increased the AS by 11% due to the maintained standard metabolic rate and increased maximum metabolic rate at higher temperature, and the AS improvement seemed greater at higher nitrate concentration. Warm-acclimated fish exposed to 200 mg NO 3 - L -1 were less susceptible to acute hypoxia, and fish acclimated at higher temperature exhibited improved heat tolerance (critical thermal maxima, CTMax) by 5 °C. This cross-tolerance can be attributed to the hematological results including maintained haemoglobin and increased haematocrit levels that may have compensated for the initial surge in methaemoglobin at higher nitrate exposure.

Standard metabolic rate (SMR) and maximum metabolic rate (MMR) were determined for Nile tilapia acclimated to six different experimental temperatures from 18 °C to 38 °C. SMR increased exponentially with temperature, from 79.8 mg O 2 kg -1 h -1 at 18 °C, to 255.1 mg O 2 kg -1 h -1 at 38 °C (Q 10 = 1.79). The main increase in Q 10 occurred within the highest temperature range, whereas in the lower temperature from 18 °C to 22 °C, temperature did not significantly affect SMR. MMR showed a hyperbolic correlation with increasing temperature, rising from 240.5 mg O 2 kg -1 h -1 at 18 °C to a peak of 373.8 mg O 2 kg -1 h -1 at 30 °C, before decreasing again at higher temperatures. Absolute aerobic scope (AAS) peaked at 26.0 °C, which we conclude to be the optimal temperature for Nile tilapia. The optimal temperature range, defined as the thermal range where 80% or more of the metabolic scope (MS) can be maintained, occurred between 19.5 and 32.1 °C. The lower (TC MIN ) and upper (TC MAX ) critical temperatures occurred at 13.1 °C and 38.8 °C. Nile tilapia showed a 4-fold scope for increasing ventilation frequency from 24 opercular beats min -1 (OB min -1 ) during SMR at 18 °C, to a maximum of 100 OB min -1 which occurred during MMR at 34 °C. f V during MMR increased with temperature, but above 30 °C became uncoupled with MO 2, as fish were unable to sustain their rates of oxygen consumption despite a high f V. There was a strong correlation between f V and SMR (r 2 = 0.83) across all temperatures indicating that f V is a good predictor of SMR. However, the correlation between MMR and f V was weak (r 2 = 0.06), due to a strong interacting effect of temperature. When selecting data from the thermal optimum range, a good correlation between f V and MO 2 was obtained (r 2 = 0.74).

In this study we investigated potential impacts of Cu exposure at low, environmentally relevant, concentrations on early live stages of Atlantic cod ( Gadus morhua ). Cod embryos and larvae were exposed to 0.5 μg/L (low), 2 μg/L (medium), and 6 μg/L (high) Cu from 4 to 17 days post fertilisation (dpf). Hatching success, mortality, oxygen consumption, biometric traits, and malformations were determined. A dynamic energy budget (DEB) model was applied to identify potential impacts on bioenergetics. A positive correlation was found between Cu exposure concentrations and Cu body burden in eggs, but not in larvae. The tested concentrations did not increase mortality in neither embryos nor larvae, or larvae deformations. Further, the DEB model did not indicate effects of the tested Cu concentrations.

Anthropogenic releases of plastics, persistent organic pollutants (POPs), and heavy metals can impact the environment, including aquatic ecosystems. Nanoplastics (NPs) have recently emerged as pervasive environmental pollutants that have the ability to adsorb POPs and can cause stress in organisms. Among POPs, DDT and its metabolites are ubiquitous environmental pollutants due to their long persistence. Despite the discontinued use of DDT in Europe, DDT and its metabolites (primarily p,p'-DDE) are still found at detectable levels in fish feed used in salmon aquaculture. Our study aimed to look at the individual and combined toxicity of NPs (50 mg/L polystyrene) and DDE (100 μg/L) using zebrafish larvae as a model. We found no significant morphological, cardiac, respiratory, or behavioural changes in zebrafish larvae exposed to NPs alone. Conversely, morphological, cardiac and respiratory alterations were observed in zebrafish larvae exposed to DDE and NPs + DDE. Interestingly, behavioural changes were only observed in zebrafish larvae exposed to NPs + DDE. These findings were supported by RNA-seq results, which showed that some cardiac, vascular, and immunogenic pathways were downregulated only in zebrafish larvae exposed to NPs + DDE. In summary, we found an enhanced toxicological impact of DDE when combined with NPs.

Many aquatic insects are exposed to the dual stressors of heavy metal pollution and rising water temperatures from global warming. These stresses may interact and have stronger impacts on aquatic organisms if heavy metals interfere with the ability of these organisms to handle high temperatures. Here we focus on the effect of copper on upper thermal limits of giant salmonfly nymphs (Order: Plecoptera, Pteronarcys californica), a stonefly species which is common in parts of western North America. Experimental exposure to copper reduced upper thermal limits by ∼ 10 °C in some cases and depressed the hypoxia tolerance (P crit ) of nymphs by ∼ 0.5 mg L -1 DO. These results suggest that copper inhibits the delivery of oxygen, which may explain, in part, the strong reductions in CT MAX that we report. Fluorescence microscopy of Cu-exposed individuals indicated high levels of copper in chloride cells but no clear evidence of damage to or high levels of copper on the gills themselves. Our study indicates that populations of aquatic insects from copper-polluted environments may be further at risk to future warming than those from uncontaminated environments.

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is the most widely used antioxidant in automobile tyres and many rubber products. We investigated the impact of 6PPD and 6PPD quinone on acute toxicity, morphology, swimming behaviour, heart rate, and oxygen consumption in zebrafish larvae. Zebrafish embryos were exposed to 6PPD and 6PPD quinone at concentrations of 1, 10, and 25 µg/L during the development period of 1-96 hpf. In the present study, 6PPD quinone was found to be toxic to zebrafish larvae with a 24 h LC 50 of 308.67 µg/L. No significant mortality was observed at any of the tested concentrations. A dose-dependent reduction in swimming performance was observed in the exposed larvae at 116 hpf for both toxicants. Overall, our study shows that exposure of zebrafish embryos to 6PPD and 6PPD quinone at environmentally relevant concentrations (1 µg/L) does not affect its behaviour. However, exposure to higher but still sublethal concentrations of 6PPD and 6PPD quinone (10 and 25 µg/L) can affect behavioural endpoints. These findings reveal the toxicity of 6PPD and 6PPD quinone to early life stages of fish.

The Antarctic ecosystem is progressively exposed to anthropogenic contaminants, such as polycyclic aromatic hydrocarbons (PAHs). So far, it is largely unknown if PAHs leave a mark in the physiology of high-Antarctic fish. We approached this issue via two avenues: first, we examined the functional response of the aryl hydrocarbon receptor (Ahr), which is a molecular initiating event of many toxic effects of PAHs in biota. Chionodraco hamatus and Trematomus loennbergii served as representatives for high-Antarctic Notothenioids, and Atlantic cod, Gadus morhua as non-polar reference species. We sequenced and cloned the Ahr ligand binding domain (LBD) of the Notothenioids and deployed a GAL4-based luciferase reporter gene assay expressing the Ahr LBD. Benzo[a]pyrene (BaP), beta-naphthoflavone and chrysene were used as ligands for the reporter gene assay. Second, we investigated the energetic costs of Ahr activation in isolated liver cells of the Notothenioids during acute, non-cytotoxic BaP exposure. In the reporter assay, the Ahr LBD of Atlantic cod and the Antarctic Notothenioids were activated by the ligands tested herein. In the in vitro assays with isolated liver cells of high-Antarctic Notothenioids, BaP exposure had no effect on overall respiration, but caused shifts in the respiration dedicated to protein synthesis. Thus, our study demonstrated that high-Antarctic fish possess a functional Ahr that can be ligand-activated in a concentration-dependent manner by environmental contaminants. This is associated with altered cost for cellular protein synthesis. Future studies have to show if the toxicant-induced activation of the Ahr pathway may lead to altered organism performance of Antarctic fish.

Like all taxa, populations of aquatic insects may respond to climate change by evolving new physiologies or behaviors, shifting their range, exhibiting physiological and behavioral plasticity, or going extinct. We evaluated the importance of plasticity by measuring changes in growth, survival and respiratory phenotypes of salmonfly nymphs (the stonefly Pteronarcys californica) in response to experimental combinations of dissolved oxygen and temperature. Overall, smaller individuals grew more rapidly during the 6-week experimental period, and oxygen and temperature interacted to affect growth in complex ways. Survival was lower for the warm treatment, although only four mortalities occurred (91.6% versus 100%). Nymphs acclimated to warmer temperatures did not have higher critical thermal maxima (CTmax), but those acclimated to hypoxia had CTmax values (in normoxia) that were higher by approximately 1°C. These results suggest possible adaptive plasticity of systems for taking up or delivering oxygen. We examined these possibilities by measuring the oxygen sensitivity of metabolic rates and the morphologies of tracheal gill tufts located ventrally on thoracic segments. Mass-specific metabolic rates of individuals acclimated to warmer temperatures were higher in acute hypoxia but lower in normoxia, regardless of their recent history of oxygen exposure during acclimation. The morphology of gill filaments, however, changed in ways that appeared to depress rates of oxygen delivery in functional hypoxia. Our combined results from multiple performance metrics indicate that rising temperatures and hypoxia may interact to magnify the risks to aquatic insects, but that physiological plasticity in respiratory phenotypes may offset some of these risks.

In this study, ballan wrasse Labrus bergylta were subjected to either a conventional 1-day or an extended 5-day respirometry protocol. Additionally, in the 5-day protocol the fish were subjected to a 12-hour light-dark cycle to assess effects of photoperiods on metabolic rates (ṀO2 ). Diurnal patterns in routine and resting ṀO2 were not observed, suggesting that circadian rhythms in metabolism largely are driven by activity patterns rather than being of endogenous origin. Moreover, lack of a detectable circadian ṀO2 may be an adaptation to lower costs of living in ballan wrasse. Protocol length influenced standard metabolic rates (SMR) where estimates decreased by 13% and 17% when using 48 hours and 5 days, respectively, compared to 24 hours. The maximum metabolic rate (MMR) and the derived absolute aerobic scope (MMR- SMR) were unaffected by protocol length. However, factorial scopes (MMR / SMR) were reduced from 8.5 to 6.4 in the 5-day protocol, showing that factorial scopes are more sensitive to how SMR are obtained. The critical oxygen tension (Pcrit ) was reduced from 15% PO2 in the 1-day group to 11% PO2 in the 5-day group. However, ṀO2 in response to decreasing PO2 was similar, which together with a similar oxygen extraction coefficient, α (ṀO2 /PO2 ), suggested that the higher Pcrit in the 1-day group was an artefact of overestimating SMR. Finally, α was 12% lower at MMR compared to at Pcrit, which either means that MMR was underestimated in proportion to this difference or that α is not constant in the entire PO2 range. In summary, this study found that a conventional 1-day respirometry protocol may overestimate SMR and thereby alter the derived Pcrit and aerobic scope, while α is unaffected by protocol length. Moreover, alternating light conditions in the absence of other stressors did not influence ṀO2 in ballan wrasse. This article is protected by copyright. All rights reserved.

Parasites are widespread in nature, where they affect the energy budget of hosts, and depending on the imposed pathogenic severity, this may reduce host fitness. However, the energetic costs of parasite infections are rarely quantified. In this study, we measured metabolic rates in recently seawater adapted Atlantic salmon (Salmo salar) infected with the ectoparasitic copepod Lepeophtheirus salmonis and used an aerobic scope framework to assess the potential ecological impact of this parasite–host interaction. The early chalimus stages of L. salmonis did not affect either standard or maximum metabolic rates. However, the later mobile pre-adult stages caused an increase in both standard and maximum metabolic rate yielding a preserved aerobic scope. Notably, standard metabolic rates were elevated by 26%, presumably caused by increased osmoregulatory burdens and costs of mobilizing immune responses. The positive impact on maximum metabolic rates was unexpected and suggests that fish are able to transiently overcompensate energy production to endure the burden of parasites and thus allow for continuation of normal activities. However, infected fish are known to suffer reduced growth, and this suggests that a trade-off exists in acquisition and assimilation of resources despite an uncompromised aerobic scope. As such, when assessing impacts of environmental or biotic factors, we suggest that elevated routine costs may be a stronger predictor of reduced fitness than the available aerobic scope. Furthermore, studying the effects on parasitized fish in an ecophysiological context deserves more attention, especially considering interacting effects of other stressors in the Anthropocene.

Aerobic metabolism generates 15–20 times more energy (ATP) than anaerobic metabolism, which is crucial in maintaining energy budgets in animals, fueling metabolism, activity, growth and reproduction. For ectothermic water‐breathers such as fishes, low dissolved oxygen may limit oxygen uptake and hence aerobic metabolism. Here, we assess, within a phylogenetic context, how abiotic and biotic drivers explain the variation in hypoxia tolerance observed in fishes. To do so, we assembled a database of hypoxia tolerance, measured as critical oxygen tensions ( P crit ) for 195 fish species. Overall, we found that hypoxia tolerance has a clear phylogenetic signal and is further modulated by temperature, body mass, cell size, salinity and metabolic rate. Marine fishes were more susceptible to hypoxia than freshwater fishes. This pattern is consistent with greater fluctuations in oxygen and temperature in freshwater habitats. Fishes with higher oxygen requirements (e.g. a high metabolic rate relative to body mass) also were more susceptible to hypoxia. We also found evidence that hypoxia and warming can act synergistically, as hypoxia tolerance was generally lower in warmer waters. However, we found significant interactions between temperature and the body and cell size of a fish. Constraints in oxygen uptake related to cellular surface area to volume ratios and effects of viscosity on the thickness of the boundary layers enveloping the gills could explain these thermal dependencies. The lower hypoxia tolerance in warmer waters was particularly pronounced for fishes with larger bodies and larger cell sizes. Previous studies have found a wide diversity in the direction and strength of relationships between P crit and body mass. By including interactions with temperature, our study may help resolve these divergent findings, explaining the size dependency of hypoxia tolerance in fish.

This study asked whether interindividual variation in maximum and standard aerobic metabolic rates of the Gulf killifish, Fundulus grandis, correlate with gill morphology and cardiac mitochondrial bioenergetics, traits reflecting critical steps in the O2 transport cascade from the environment to the tissues. Maximum metabolic rate (MMR) was positively related to body mass, total gill filament length, and myocardial oxygen consumption during maximum oxidative phosphorylation (multiple R2=0.836). Standard metabolic rate (SMR) was positively related to body mass, total gill filament length, and myocardial oxygen consumption during maximum electron transport system activity (multiple R2=0.717). After controlling for body mass, individuals with longer gill filaments, summed over all gill arches, or greater cardiac respiratory capacity had higher whole-animal metabolic rates. The overall model fit and the explanatory power of individual predictor variables were better for MMR than for SMR, suggesting that gill morphology and myocardial bioenergetics are more important in determining active rather than resting metabolism. After accounting for body mass, heart ventricle mass was not related to variation in MMR or SMR, indicating that the quality of the heart (i.e., the capacity for mitochondrial metabolism) was more influential than heart size. Finally, the myocardial oxygen consumption required to offset the dissipation of the transmembrane proton gradient in the absence of ATP synthesis was not correlated with either MMR or SMR. The results support the idea that interindividual variation in aerobic metabolism, particularly maximum metabolic rate, is associated with variation in specific steps in the O2 transport cascade.

The critical oxygen tension (Pcrit) for fishes is the oxygen level below which oxygen consumption (MO2) becomes dependent upon ambient oxygen partial pressure (PO2). We compare multiple curve-fitting approaches to estimate Pcrit of the Gulf killifish, Fundulus grandis Baird Girard, 1853, during closed and intermittent-flow respirometry. Fitting two line segments of MO2 versus PO2 produced high and variable estimates of Pcrit, as did nonlinear regression using a hyperbolic (Michaelis-Menton) function. Using nonlinear regression fit to an exponential (modified Weibull) function, or linear regression of MO2 versus PO2 at low PO2, and determining Pcrit as the PO2 when MO2 equals standard metabolic rate (SMR) yielded values that were consistent across fish and among experimental trials. The magnitude of the difference in Pcrit determined by alternative calculation methods exceeded the differences determined in closed and intermittent-flow respirometry, highlighting the need to standardize analytical as well as experimental approaches in determining Pcrit.

Copepods dominate zooplankton biomass of the upper ocean, especially in the highly seasonal northern boreal and Polar Regions, for which specific life-cycle traits such as the accumulation of lipid reserves, migration into deep water, and diapause, are key adaptations. Understanding such traits is central to determining the energetic consequences of high latitude range shifts related to climate change and ultimately, biogeochemical models of carbon flow. Using the calanoid copepod Calanus finmarchicus, we explore a new indicator of diapause, swimming activity, and assess its relationship with respiration. Stage CV copepods were sampled in late summer from shallow (epipelagic) and deep (mesopelagic) water at both on-shelf and off-shelf locations within the Fram Strait at a time when the animals had entered diapause. Using high-throughput quantitative behaviour screening on ex situ swimming activity, we found that irrespective of sampling station copepods from the mesopelagic show highly reduced activity (88.5 ± 3.4 % reduction) when compared to those from the epipelagic. This was supported by morphometric analyses which found that copepods from the mesopelagic were generally larger (12.4 ± 8.8 % increase) and had more lipid reserves (19.3 ± 2.2 % increase) than epipelagic individuals. On average, copepods from the off-shelf station exhibited respiration rates similar to overwintering rates observed elsewhere (1.23 ± 0.76 µg C d-1), while respiration rates of copepods from the shelf station were more consistent with active metabolism (2.46 ± 1.02 µg C d-1). Nevertheless, active and diapausing rates were observed in individuals from both stations at both epi- and mesopelagic depths. We suggest that rapid screening of activity may provide an early indicator of diapause before it becomes fully apparent and consistent in other physiological indicators. Ultimately, swimming activity may provide a useful tool to assess the putative endogenous and exogenous factors involved in diapause onset, provide a handle on the energetics of diapause, and input to biogeochemical carbon models on C. finmarchicus.

Venlafaxine, a selective serotonin and norepinephrine reuptake inhibitor, is a widely prescribed antidepressant that is detected in municipal wastewater effluents at µg/L concentrations. It has been shown to impact the early life stages of fish, including neurodevelopment and behaviour in larvae, but whether such early exposures have longer-term consequences are far from clear. Here, we sought to determine whether zygotic deposition of venlafaxine, mimicking a maternal transfer scenario, disturbs the metabolic rate and behavioural performance using zebrafish (Danio rerio). This was tested using freshly fertilized embryos (1–4 cell stage) microinjected with either 0, 1 or 10 ng of venlafaxine and raised to either juvenile (60 days post-fertilization) or adult (10–12 months post-fertilization). Zygotic venlafaxine exposure led to a reduction in the active metabolic rate and aerobic scope, but this was only observed in female fish. On the other hand, the total distance travelled in an open field assessment was greater at the highest concentration of venlafaxine only in the adult males. At the juvenile stage, behavioural assessments demonstrated that venlafaxine exposure may increase boldness—including hyperactivity, lower thigmotaxis, and a reduction in the distance to a novel object. Taken together, these results demonstrate that zygotic venlafaxine exposure may impact developmental programming in a sex-specific manner in fish.

In many cases, understanding species’ responses to climate change requires understanding variation among individuals in response to such change. For species with strong symbiotic relationships, such as many coral reef species, genetic variation in symbiont responses to temperature may affect the response to increased ocean temperatures. To assess variation among symbiont genotypes, we examined the population dynamics and physiological responses of genotypes of Breviolum antillogorgium in response to increased temperature. We found broad temperature tolerance across genotypes, with all genotypes showing positive growth at 26, 30, and 32°C. Genotypes differed in the magnitude of the response of growth rate and carrying capacity to increasing temperature, suggesting that natural selection could favor different genotypes at different temperatures. However, the historical temperature at which genotypes were reared (26 or 30°C) was not a good predictor of contemporary temperature response. We found increased photosynthetic rates and decreased respiration rates with increasing contemporary temperature, and differences in physiology among genotypes, but found no significant differences in the response of these traits to temperature among genotypes. In species with such broad thermal tolerance, selection experiments on symbionts outside of the host may not yield results sufficient for evolutionary rescue from climate change.

The red swamp crayfish (Procambarus clarkii) is the most widely spread freshwater crayfish worldwide. Competing physiological traits can influence invasion success in any given environment by limiting the available scope for aerobically demanding activities. While high flows have been associated with reduced crayfish movement upstream, the effects of flow alteration on their metabolic demands have been largely overlooked. In this study, we estimated routine metabolic rate (RMR) at rest and oxygen consumption rates of crayfish under different current velocities in a flume respirometer, while maximum metabolic rate (MMR) was determined using the exhaustive chase protocol. We also measured some morphometric variables in males and females of crayfish. Oxygen uptake substantially increased with crayfish size and current velocity due to increased energy expenditure to overcome drag and hold a stationary position. Sexual dimorphism in morphological traits did not lead to sexual differences in oxygen uptake. Moreover, we found that individuals operated close to their maximum aerobic capacity at elevated current velocities (≥ 25 cm s−1). This suggested that the high flow-driven energetic demand may compromise the energy available for reproduction, growth and dispersal, thereby affecting overall fitness. These metabolic constraints could partly explain the failed invasions of invasive crayfish in fast-flowing waters.

Chemical UV filters are increasingly used in cosmetics to protect skin from UV radiation. As a consequence, they are released into the aquatic environment via recreational activities and wastewaters. In aquatic ecosystems, fish eggs in contact with sediment can be affected by organic and lipophilic pollutants such as UV filters. The present study aims to evaluate the toxicity of six individual UV filters, diethylhexyl butamido triazone (DBT), diethylamino hydroxybenzoyl hexyl benzoate (DHHB), ethylhexyl triazone (ET), 2-ethylhexyl salicylate (ES), homosalate (HS), and octocrylene (OC), in the embryo-larval stages of zebrafish Danio rerio. Contamination of fish eggs and larvae with UV filters occurred through contact with spiked sediment for 96 h at a concentration of 10 μg g−1. Among the six UV filters tested, OC delayed hatching success, whereas ES significantly increased the heartbeat rate of embryo–larvae after sediment exposure, probably as a stress response.

Obesity and metabolic syndrome are of increasing global concern. In order to understand the basic biology and etiology of obesity, research has turned to animals across the vertebrate spectrum including zebrafish. Here, we carefully characterize zebrafish in a long-term obesogenic environment as well as zebrafish that went through early lifetime caloric restriction. We found that long-term obesity in zebrafish leads to metabolic endpoints comparable to mammals including increased adiposity, weight, hepatic steatosis and hepatic lesions but not signs of glucose dysregulation or differences in metabolic rate or mitochondrial function. Malnutrition in early life has been linked to an increased likelihood to develop and an exacerbation of metabolic syndrome, however fish that were calorically restricted from five days after fertilization until three to nine months of age did not show signs of an exacerbated phenotype. In contrast, the groups that were shifted later in life from caloric restriction to the obesogenic environment did not completely catch up to the long-term obesity group by the end of our experiment. This dataset provides insight into a slowly exacerbating time-course of obesity phenotypes.

In animals living in groups, the social environment is fundamental to shaping the behaviors and life histories of an individual. A mismatch between individual and group behavior patterns may have disadvantages if the individual is incapable of flexibly changing its state in response to the social environment that influences its energy gain and expenditure. We used different social groups of juvenile three‐spined sticklebacks ( Gasterosteus aculeatus ) with experimentally manipulated compositions of individual sociability to study the feedback between individual and group behaviors and to test how the social environment shapes behavior, metabolic rate, and growth. Experimentally created unsociable groups, containing a high proportion of less sociable fish, showed bolder collective behaviors during feeding than did corresponding sociable groups. Fish within groups where the majority of members had a level of sociability similar to their own gained more mass than did those within mismatched groups. Less sociable individuals within sociable groups tended to have a relatively low mass but a high standard metabolic rate. A mismatch between the sociability of an individual and that of the majority of the group in which it is living confers a growth disadvantage probably due to the expression of nonadaptive behaviors that increase energetic costs.

The physiological response of two species of mussels ( Mytilus edulis and M. galloprovincialis ) and two species of oysters ( Crassostrea gigas and Ostrea edulis ) to temperature, oxygen levels and food concentration, factors likely to vary as a result of climate change, was determined experimentally. Bivalves of similar size from different origins were exposed to six temperatures (3, 8, 15, 20, 25 and 30 °C) at two food regimes (2 and 10 μg Chl a L −1 ) for 6 weeks. In a parallel running experiment M. edulis from the same batches were exposed to three different temperatures (15, 20 and 25 °C) and three different oxygen levels (30, 50 and 100%) at two food regimes (2 and >8 μg Chl a L −1 ) for 3–4 weeks. Survival during the experiment ranged from 93% to 100% except for the mussels exposed to 30 °C which showed 100% mortality after three to 32 days. Higher food conditions showed higher optimal temperatures for growth of mussels and oysters. In addition, at the high food treatment, reduced O 2 saturation resulted in lower growth of mussels. At the low food treatment there were no differences in growth among the different O 2 levels at the same temperature. At high food concentration treatment, M. edulis growth was higher with low temperature and high oxygen level. Condition index was higher at higher food concentrations and decreased with increasing temperature. In addition, condition was lower at low oxygen saturation. Lower clearance rates were observed at high food concentrations. At 100% saturation of oxygen, mussel clearance rate increased with temperature at High food regime, but not at Low food regime. Mussel clearance rates were significantly reduced with low oxygen concentrations together with high temperature. Oxygen consumption significantly increased with temperature. Oxygen saturation was the main factor affecting mussel clearance rate. High temperature and low oxygen concentration combined significantly reduced clearance rate and increased oxygen consumption. These response curves can be used to improve parameterisation of individual shellfish growth models taking into consideration factors in the context of climate change: temperature, food concentration, oxygen concentration and their interactions. The observation that abiotic factors interact in affecting mussels and oysters is an important result to take into account.

Aim Although zebrafish are gaining popularity as biomedical models of cardiovascular disease, our understanding of their cardiac control mechanisms is fragmentary. Our goal was to clarify the controversial role of the ß1‐adrenergic receptor (AR) in the regulation of heart rate in zebrafish. Methods CRISPR‐Cas9 was used to delete the adrb1 gene in zebrafish allowing us to generate a stable adrb1 −/− line. Larval heart rates were measured during pharmacological protocols and with exposure to hypercapnia. Expression of the five zebrafish adrb genes were measured in larval zebrafish hearts using qPCR. Results Compared with genetically matched wild‐types ( adrb1 +/+ ), adrb1 −/− larvae exhibited ~20 beats min −1 lower heart rate, measured from 2 to 21 days post‐fertilization (dpf). Nevertheless, adrb1 −/− larvae exhibited preserved positive chronotropic responses to pharmacological treatment with AR agonists (adrenaline, noradrenaline, isoproterenol), which were blocked by propranolol (general ß‐AR antagonist). Regardless of genotype, larvae exhibited similar increases in heart rate in response to hypercapnia (1% CO 2 ) at 5 dpf, but tachycardia was blunted in adrb1 −/− larvae at 6 dpf. adrb1 gene expression was abolished in the hearts of adrb1 −/− larvae, confirming successful knockout. While gene expression of adrb2a and adrb3a was unchanged, adrb2b and adrb3b mRNA levels increased in adrb1 −/− larval hearts. Conclusion Despite adrb1 contributing to the setting of resting heart rate in larvae, it is not strictly essential for zebrafish, as we generated a viable and breeding adrb1 −/− line. The chronotropic effects of adrenergic stimulation persist in adrb1 −/− zebrafish, likely due to the upregulation of other ß‐AR subtypes.

The amazon fishes’ responses to hypoxia seem to be related to the Amazon basin diversity of aquatic environments, which present drastic daily and seasonal variations in the dissolved oxygen concentration. Among these fishes’ adaptation to hypoxia, behavioral, metabolic, physiological, and biochemical responses are well known for some species. In this work, we aimed to identify how two different aquatic environments, normoxic forest streams and hypoxic lakes, dictate the responses to hypoxia for two cichlid species, Mesonauta festivus and Aequidens pallidus. In our results, we found that A. pallidus is less tolerant to hypoxia, which seems to be related to this animal’s natural normoxic environment. Even though this species modulated the mitochondrial respiration in order to improve the oxygen use, it also showed a lower decrease in metabolic rate when exposed to hypoxia and no activation of the anaerobic metabolism. Instead, M. festivus showed a higher decrease in metabolic rate and an activation of the anaerobic metabolism. Our data reveal that the natural dissolved oxygen influences the hypoxia tolerance and the species’ tolerance is related to its ability to perform metabolic depression. The interest results are the absence of mitochondrial respiration influences in these processes. The results observed with A. pallidus bring to light also the importance of preserving the forests, in which streams hold very specialized species acclimated to normoxia and lower temperature. The importance of hypoxia tolerance is, thus, important to keep fish assemblage and is thought to be a strong driver of fish biodiversity.

Significance Biology has long-standing rules about how metabolism and demography should covary. These rules connect physiology to ecology but remarkably, these rules have only ever been tested indirectly. Using a model marine invertebrate, we created experimental field populations that varied in metabolic rate but not body size. We show that metabolism qualitatively affects population growth and carrying capacity in ways predicted by theory but that scaling relationships for these parameters, as well as estimates of energy use at carrying capacity, depart from classic predictions. That metabolism affects demography in ways that depart from canonical theory has important implications for predicting how populations may respond to global change and size-selective harvesting. Metabolism should drive demography by determining the rates of both biological work and resource demand. Long-standing “rules” for how metabolism should covary with demography permeate biology, from predicting the impacts of climate change to managing fisheries. Evidence for these rules is almost exclusively indirect and in the form of among-species comparisons, while direct evidence is exceptionally rare. In a manipulative field experiment on a sessile marine invertebrate, we created experimental populations that varied in population size (density) and metabolic rate, but not body size. We then tested key theoretical predictions regarding relationships between metabolism and demography by parameterizing population models with lifetime performance data from our field experiment. We found that populations with higher metabolisms had greater intrinsic rates of increase and lower carrying capacities, in qualitative accordance with classic theory. We also found important departures from theory—in particular, carrying capacity declined less steeply than predicted, such that energy use at equilibrium increased with metabolic rate, violating the long-standing axiom of energy equivalence. Theory holds that energy equivalence emerges because resource supply is assumed to be independent of metabolic rate. We find this assumption to be violated under real-world conditions, with potentially far-reaching consequences for the management of biological systems.

Animals inhabiting the intertidal zone are exposed to abrupt changes in environmental conditions associated with the rise and fall of the tide. For convenience, the majority of laboratory studies on intertidal organisms have acclimated individuals to permanently submerged conditions in seawater tanks. In this study, green shore crabs, Carcinus maenas, were acclimated to either a simulated tidal regime of continuous emersion–immersion (‘tidal’) or to permanently submerged conditions (‘non-tidal’) to assess their physiological responses to subsequent emersion. Tidal crabs exhibited an endogenous rhythm of oxygen consumption during continuous submersion with lower oxygen consumption during periods of anticipated emersion, which was not detected in non-tidal crabs. During emersion, tidal crabs were able to buffer apparent changes in acid–base balance and exhibited no change in venous pH, whereas non-tidal crabs developed an acidosis associated with a rise in lactate levels. These results indicate that tidal crabs were better able to sustain aerobic metabolism and had lower metabolic costs during emersion than non-tidal crabs. It is likely that the elevated levels of haemocyanin exhibited by tidal crabs allowed them to maintain oxygen transport and buffer pH changes during emersion. This suggests that acclimation of C. maenas to submerged conditions results in a loss of important physiological mechanisms that enable it to tolerate emersion. The results of this study show that caution must be taken when acclimating intertidal organisms to submerged conditions in the laboratory, as it may abolish important physiological responses and adaptations that are critical to their performance when exposed to air.

Food availability and temperature influence energetics of animals and can alter behavioral responses such as foraging and spontaneous activity. Food availability, however, is not necessarily a good indicator of energy (ATP) available for cellular processes. The efficiency of energy transduction from food‐derived substrate to ATP in mitochondria can change with environmental context. Our aim was to determine whether the interaction between food availability and temperature affects mitochondrial efficiency and behavior in zebrafish ( Danio rerio ). We conducted a fully factorial experiment to test the effects of feeding frequency, acclimation temperature (three weeks to 18 or 28°C), and acute test temperature (18 and 28°C) on whole‐animal oxygen consumption, mitochondrial bioenergetics and efficiency (ADP consumed per oxygen atom; P:O ratio), and behavior (boldness and exploration). We show that infrequently fed (once per day on four days per week) zebrafish have greater mitochondrial efficiency than frequently fed (three times per day on five days per week) animals, particularly when warm‐acclimated. The interaction between temperature and feeding frequency influenced exploration of a novel environment, but not boldness. Both resting rate of producing ATP and scope for increasing it were positively correlated with time spent exploring and distance moved in standardized trials. In contrast, behavior was not associated with whole‐animal aerobic (oxygen consumption) scope, but exploration was positively correlated with resting oxygen consumption rates. We highlight the importance of variation in both metabolic (oxygen consumption) rate and efficiency of producing ATP in determining animal performance and behavior. Oxygen consumption represents energy use, and P:O ratio is a variable that determines how much of that energy is allocated to ATP production. Our results emphasize the need to integrate whole‐animal responses with subcellular traits to evaluate the impact of environmental conditions on behavior and movement.

Long-term imbalance between fatigue and recovery may eventually lead to muscle weakness or even atrophy. We previously reported that excessive exercise induces pathological cardiac hypertrophy. However, the effect of excessive exercise on the skeletal muscles remains unclear. In the present study, we successfully established an excessive-exercise-induced skeletal muscle atrophy zebrafish model, with decreased muscle fiber size, critical swimming speed, and maximal oxygen consumption. High-throughput RNA-seq analysis identified differentially expressed genes in the model system compared with control zebrafish. Gene ontology and KEGG enrichment analysis revealed that the upregulated genes were enriched in autophagy, homeostasis, circadian rhythm, response to oxidative stress, apoptosis, the p53 signaling pathway, and the FoxO signaling pathway. Protein–protein interaction network analysis identified several hub genes, including keap1b, per3, ulk1b, socs2, esrp1, bcl2l1, hsp70, igf2r, mdm2, rab18a, col1a1a, fn1a, ppih, tpx2, uba5, nhlrc2, mcm4, tac1, b3gat3, and ddost, that correlate with the pathogenesis of skeletal muscle atrophy induced by excessive exercise. The underlying regulatory pathways and muscle-pressure-response-related genes identified in the present study will provide valuable insights for prescribing safe and accurate exercise programs for athletes and the supervision and clinical treatment of muscle atrophy induced by excessive exercise.

The UAB Nathan Shock Center focuses on comparative energetics and aging. Energetics, as defined for this purpose, encompasses the causes, mechanisms, and consequences of the acquisition, storage, and use of metabolizable energy. Comparative energetics is the study of metabolic processes at multiple scales and across multiple species as it relates to health and aging. The link between energetics and aging is increasingly understood in terms of dysregulated mitochondrial function, altered metabolic signaling, and aberrant nutrient responsiveness with increasing age. The center offers world-class expertise in comprehensive, integrated energetic assessment and analysis from the level of the organelle to the organism and across species from the size of worms to rats as well as state-of-the-art data analytics. The range of services offered by our three research cores, (1) The Organismal Energetics Core, (2) Mitometabolism Core, and (3) Data Analytics Core, is described herein.

The purpose of this study was to investigate if the cardiovascular system is important for ammonia excretion in the early life stages of zebrafish. Morpholino knockdowns of cardiac troponin T (TNNT2) or vascular endothelial growth factor A (VEGFA) provided morphants with nonfunctional circulation. At the embryonic stage [30–36 h postfertilization (hpf)], ammonia excretion was not constrained by a lack of cardiovascular function. At 2 days postfertilization (dpf) and 4 dpf, morpholino knockdowns of TNNT2 or VEGFA significantly reduced ammonia excretion in all morphants. Expression of rhag, rhbg, and rhcgb showed no significant changes but the mRNA levels of the urea transporter ( ut) were upregulated in the 4 dpf morphants. Taken together, rhag, rhbg, rhcgb, and ut gene expression and an unchanged tissue ammonia concentration but an increased tissue urea concentration, suggest that impaired ammonia excretion led to increased urea synthesis. However, in larvae anesthetized with tricaine or clove oil, ammonia excretion was not reduced in the 4 dpf morphants compared with controls. Furthermore, oxygen consumption was reduced in morphants regardless of anesthesia. These results suggest that cardiovascular function is not directly involved in ammonia excretion, but rather reduced activity and external convection may explain reduced ammonia excretion and compensatory urea accumulation in morphants with reduced cardiovascular function.

It is now recognized that parental diets could highly affect offspring metabolism and growth. Studies in fish are, however, lacking. In particular, the effect of a parental diet high in carbohydrate (HC) and low in protein (LP) on progeny has never been examined in higher trophic level teleost fish. Thus, two-year old male and female rainbow trout (Oncorhynchus mykiss) were fed either a control diet (0% carbohydrate and 63.89% protein) or a diet containing 35% carbohydrate and 42.96% protein (HC/LP) for a complete reproductive cycle for females and over a 5-month period for males. Cross-fertilizations were then carried out. To evaluate the effect of the parental diet on their offspring, different phenotypic and metabolic traits were recorded for offspring before their first feeding and again three weeks later. When considering the paternal and maternal HC/LP nutrition independently, fry phenotypes and transcriptomes were only slightly affected. The combination of the maternal and paternal HC/LP diets altered the energy metabolism and mitochondrial dynamics of their progeny, demonstrating the existence of a synergistic effect. The global DNA methylation of whole fry was also highly affected by the HC/LP parental diet, indicating that it could be one of the fundamental mechanisms responsible for the effects of nutritional programming.

Hypoxia is a growing concern in aquatic ecosystems. Historically, scientists have used the P crit (the dissolved oxygen level below which an animal can no longer oxyregulate) to infer hypoxia tolerance across species. Here, we tested the hypothesis that the P crit is positively correlated with temperature in the mayfly, Neocloeon triangulifer. Cross-temperature comparisons showed a modest ( r = 0.47), but significant ( p < 0.0001) association between temperature and P crit despite relatively large interindividual variability (Coefficient of Variance (CV) = 39.9% at 18 °C). We used the expression of hypoxia-responsive genes EGL-9 (an oxygen sensing gene and modulator of HIF-1a activity) and LDH (a hypoxia indicator) to test whether oxygen partial pressure near the P crit stimulates expression of hypoxia-responsive genes. Neither gene was upregulated at oxygen levels above the estimated P crit, however, at or below the P crit estimates, expression of both genes was stimulated (~20- and ~3-fold change for EGL-9 and LDH, respectively). Finally, we evaluated the influence of hypoxic exposure time and pretreatment conditions on the mRNA expression levels of hypoxia-responsive genes. When larvae were exposed to a gradual reduction of DO, hypoxic gene expression was more robust than during instantaneous exposure to hypoxia. Our data provide modest support for traditional interpretation of the P crit as a physiologically meaningful shift from aerobic to anaerobic metabolism in N. triangulifer. However, we also discuss limitations of the P crit as a proxy measure of hypoxia tolerance at the species level. Keywords: Hypoxia, Pcrit, Gene expression, Temperature, Mayfly

Mining and processing of minerals produce large quantities of tailings as waste. Some countries, including Norway, allow disposal of mine tailings in the sea. In this study we investigated the impacts of tailings from a calcium carbonate (CaCO 3 ) processing plant on early live stages of haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua). Fish eggs (3 days post fertilisation; dpf) were exposed for 48 h to three concentrations of tailings, nominally 1 mg L -1 (low, L); 10 mg L -1 (medium, M) and 100 mg L -1 (high, H); with L and M representing concentrations occurring at tailing release points. Results show that tailings rapidly adhered to eggs of both species, causing negative buoyancy (sinking of eggs) in M and H exposures. While tailings remained on egg surfaces in both species also after exposure termination, adhesion seemed more pronounced in cod, leading to larger impacts on buoyancy even after exposure. Tailing exposure further induced early hatching and significantly reduced survival in M and H exposed embryos in both fish species, and in cod from the L exposure group. Moreover, tailing exposure caused reduced survival and malformations in larvae, potentially related to premature hatching. This study shows that mineral particles adhere to haddock and cod eggs, affecting egg buoyancy, survival and development.

Fishes exposed to crude oil have shown reduced sociability and poor habitat selection, which corresponded with increased predation risk. However, the contribution of oil-induced cardiorespiratory impairments to these findings is uncertain. This study explores the effect of oil exposure on predation risk in a model fish species, Sciaenops ocellatus, across a suite of physiological and behavioral end points to elucidate the mechanisms through which any observed effects are manifested. Using mesocosms to assess group predator avoidance, oil exposure to 36.3 μg l -1 ΣPAH reduced the time to 50% mortality from a mean time of 80.0 (74.1-86.0 95% confidence interval [CI]) min to 39.2 (35.6-42.8 95% CI) min. The influence of oil impaired cardiorespiratory and behavioral pathways on predation risk was assessed based on respiratory performance, swim performance, sociability, and routine activity. Swim trials demonstrated that cardiorespiratory and swim performance were unaffected by exposures to 26.6 or 100.8 μg l -1 ΣPAH. Interestingly, behavioral tests revealed that exposure to 26.6 μg l -1 ΣPAH increased distance moved, speed, acceleration, and burst activity. These data indicate that behavioral impairment is more sensitive than cardiorespiratory injury and may be a more important driver of downstream ecological risk following oil exposure in marine species.

Marine tailing disposal (MTD) is sometimes practiced as an alternative to traditional mine tailing deposition on land. Environmental challenges connected to MTD include spreading of fine particulate matter in the water column and the potential release of metals and processing chemicals. This study investigated if tailing exposure affects the marine copepod Calanus finmarchicus, and whether effects are related to exposure to mineral particles or the presence of metals and/or processing chemicals in the tailings. We investigated the impacts of three different tailing compositions: calcium carbonate particles with and without processing chemicals and fine-grained tailings from a copper ore. Early life stages of C. finmarchicus were exposed over several developmental stages to low and high suspension concentrations for 15 days, and their development, oxygen consumption and biometry determined. The data was fitted in a dynamic energy budget (DEB) model to determine mechanisms underlying responses and to understand the primary modes of action related to mine tailing exposure. Results show that copepods exposed to tailings generally exhibited slower growth and accumulated less lipids. The presence of metals and processing chemicals did not influence these responses, suggesting that uptake of mineral particles was responsible for the observed effects. This was further supported by the applied DEB model, confirming that ingestion of tailing particles while feeding can result in less energy being available for growth and development.

Specific dynamic action (SDA) can be defined as the accumulated energy expended in the process of ingestion, digestion, absorption and the assimilation of the food, and there is substantial evidence that protein synthesis is responsible for most of the SDA in fish. A technique developed by Lauff and Wood (Journal of Comparative Physiology B, 1996, 165, 542; Journal of Comparative Physiology B, 1996, 166, 501), called instant quantification of energetic substrate usage, allows quantifying the utilization of lipids, carbohydrates and proteins as energy fuel in a given time, including the SDA period, based only on measurements of oxygen consumption and carbon dioxide and nitrogen excretion. Matrinxã and tambaqui are two important Amazonian fish farmed and marketed worldwide. Despite being considered omnivorous fish, they present specificities in growing, converting food and behaving, suggesting some differences in their digestive system. In the present work, we used specimens of tambaqui and matrinxã to measure metabolic rate, excretion of nitrogen and carbon dioxide and to calculate the relative and absolute use of proteins as an energy source in experimental animals. Our results suggest that small matrinxãs quickly start the anabolic process in the postprandial period and, in larger tambaqui, it occurs late, but present a longer duration. Matrinxã also shows a higher basal nitrogen excretion, which increases faster after feeding. The substrate usage calculations support the hypothesis that in small matrinxã, in initial stages of the postprandial period, the fish use mainly endogenous carbohydrates as fuel, changing into proteins in further stages.

Metabolic rates are linked to the energetic costs of different activities of an animal’s life. However, measuring the metabolic rate in free-swimming fish remains challenging due to the lack of possibilities to perform these direct measurements in the field. Thus, the calibration of acoustic transmitters with the oxygen consumption rate (MO2) could be promising to counter these limitations. In this study, rainbow trout (Oncorhynchus mykiss Walbaum, 1792; n = 40) were challenged in a critical swimming test (Ucrit) to (1) obtain insights about the aerobic and anaerobic metabolism throughout electromyograms; and (2) calibrate acoustic transmitters’ signal with the MO2 to be later used as a proxy of energetic costs. After this calibration, the fish (n = 12) were implanted with the transmitter and were followed during ~50 days in an aquaculture facility, as a case study, to evaluate the potential of such calibration. Accelerometer data gathered from tags over a long time period were converted to estimate the MO2. The MO2 values indicated that all fish were reared under conditions that did not impact their health and welfare. In addition, a diurnal pattern with higher MO2 was observed for the majority of implanted trout. In conclusion, this study provides (1) biological information about the muscular activation pattern of both red and white muscle; and (2) useful tools to estimate the energetic costs in free-ranging rainbow trout. The use of acoustic transmitters calibrated with MO2, as a proxy of energy expenditure, could be promising for welfare assessment in the aquaculture industry.

Hypoxia (low oxygen) often occurs in aquatic ecosystems that receive effluent from municipal wastewater treatment plants (WWTP). The combination of hypoxia and WWTP effluent could impair fish health, because WWTP effluent contains multiple contaminants that could disrupt the physiological pathways fish use to cope with hypoxia, but the interactive effects of these stressors on fish physiology are poorly understood. We have examined this issue by exposing mummichog killifish (Fundulus heteroclitus) to hypoxia (5 and 2 kPa O2) and/or 100% WWTP effluent for 21 days in a full factorial design. We then measured hypoxia tolerance, whole-animal metabolism, gill morphology, haematology, and tissue metabolites. In clean water, killifish responded to chronic hypoxia with improvements in hypoxia tolerance, as reflected by increases in time to loss of equilibrium at 0.5 kPa (tLOE). These improvements occurred in association with increases in the exposed surface of gill lamellae that resulted from a regression of interlamellar cell mass (ILCM). Concurrent exposure to wastewater attenuated the increases in tLOE and gill remodeling in chronic hypoxia, and nearly depleted brain glycogen stores. Therefore, exposure to WWTP effluent can disrupt the physiological mechanisms fish use to cope with chronic hypoxia and impair hypoxia tolerance. Our research suggests that the combination of stressors near WWTPs can have interactive effects on the physiology and health of fish.

Acoustic transmitters equipped with accelerometer sensors are considered a useful tool to study swimming activity, including energetics and movement patterns, of fish species in aquaculture and in nature. However, given the novelty of this technique, further laboratory-derived calibrations are needed to assess the characteristics and settings of accelerometer acoustic transmitters for different species and specific environmental conditions. In this study, we compared accelerometer acoustic transmitter outputs with swimming performance and body motion of gilthead seabream ( Sparus aurata L.) in swim-tunnels at different flow speeds, which allowed us to characterize the swimming activity of this fish species of high aquaculture interest. Tag implantation in the abdominal cavity had no significant effects on swimming performance and body motion parameters. Accelerations, cost of transport and variations on head orientation (angle with respect to flow direction) were negatively related to flow speed in the tunnel, whereas oxygen consumption and frequencies of tail-beat and head movements increased with flow speed. These results show that accelerometer acoustic transmitters mainly recorded deviations from sustained swimming in the tunnel, due to spontaneous and explorative swimming at the lowest speeds or intermittent burst and coast actions to cope with water flow. In conclusion, accelerometer acoustic transmitters applied in this study provided a proxy for unsustained swimming activity, but did not contemplate the high-energy cost spent by gilthead seabream on sustained swimming, and therefore, it did not provide a proxy for general activity. Despite this limitation, accelerometer acoustic transmitters provide valuable insight in swim patterns and therefore may be a good strategy for advancing our understanding of fish swimming behavior in aquaculture, allowing for rapid detection of changes in species-specific behavioral patterns considered indicators of fish welfare status, and assisting in the refinement of best management practices.

The physiology and behaviour of fish are strongly affected by ambient water temperature. Physiological traits related to metabolism, such as aerobic scope (AS), can be measured across temperature gradients, and the resulting performance curve reflects the thermal niche that fish can occupy. We measured AS of westslope cutthroat trout (Oncorhynchus clarkii lewisi) at 5, 10, 15, 20, and 22 °C and compared temperature preference (T pref ) of the species with non-native brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (Oncorhynchus mykiss). Intermittent-flow respirometry experiments demonstrated that metabolic performance of westslope cutthroat trout was optimal at ∼15 °C and decreased substantially beyond this temperature, until lethal temperatures at ∼25 °C. Adjusted T pref across species were comparatively high, ranging from 17.8 to 19.9 °C, with the highest T pref observed for westslope cutthroat trout. Results suggest that although westslope cutthroat trout is considered a cold-water species, they do not prefer or perform as well in cold water (≤10 °C) and thus can occupy a warmer thermal niche than previously thought. The metabolic performance curve (AS) can be used to develop species‐specific thermal criteria to delineate important thermal habitats and guide conservation and recovery actions for westslope cutthroat trout.

Stress due to handling is often an unavoidable feature of experimental investigations. In some cases, appropriate settling times are not considered, and as such, physiological responses caused by handling may become additive with those of experimental treatments. This study investigated the effect of different handling procedures on the acute physiological responses of green shore crab (Carcinus maenas). Handling, such as would occur during transport around a research facility or transfer during experimental procedure, was designated as light (10 min emersion) or severe (10 min emersion with shaking). Oxygen consumption (MO2) and haemolymph glucose and haemolymph L-lactate concentrations were elevated post-handling, the magnitude of the change related to the severity of handling stress. Glucose and L-lactate concentrations peaked within 1 h and returned to basal levels within 6 h, but MO2 remained elevated for 10 h, reflecting the additional energy required to oxidize L-lactate and replenish energy reserves. Differences between light and severe handling treatments showed that vibration (shaking) was a major contributor to the stress response, rather than the experimental emersion. This was confirmed in a second experiment where crabs were handled without emersion, and MO2 remained elevated for 14 h. In this experiment, the most pronounced increase in MO2 and metabolic parameters occurred in crabs that were physically touched and moved rapidly from the holding to experimental tanks. Here the touch, as well as vibration and visual stimuli, provoked a fight-flight response in the crabs. Stress responses were also evident in crabs gently transferred by containers. The fact that transferring crabs with no physical touching and minimal visual and vibrational stimuli still evoked a stress response, albeit less pronounced, supports a recommendation that crustaceans should be left to settle in the apparatus for at least 12 h after handling before experimental procedures are initiated.

We studied the effects of metabolic cold adaptation (MCA) in two populations of a eurythermal species, spotted seatrout (Cynoscion nebulosus) along the U.S. East Coast. Fish were captured from their natural environment and acclimated at control temperatures 15 °C or 20 °C. Their oxygen consumption rates, a proxy for metabolic rates, were measured using intermittent flow respirometry during acute temperature decrease or increase (2.5 °C per hour). Mass-specific standard metabolic rates (SMR) were higher in fish from the northern population across an ecologically relevant temperature gradient (5 °C to 30 °C). SMR were up to 37% higher in the northern population at 25 °C and maximum metabolic rates (MMR) were up to 20% higher at 20 °C. We found evidence of active metabolic compensation in the southern population from 5 °C to 15 °C (Q10

Previous studies have demonstrated that hypoxia tolerance is improved in zebrafish (Danio rerio) larvae after prior exposure to lowered ambient O2 levels. Such improved hypoxia performance was attributed in part, to increased levels of hypoxia-inducible factor 1α (Hif-1α) exerting downstream effects on various physiological processes including promotion of trunk skin angiogenesis. Since O2 uptake ( $$\dot{M}{\text{O}}_{2}$$ ) in larvae is facilitated largely by O2 diffusion across the skin, enhanced cutaneous vascularization is expected to enhance $$\dot{M}{\text{O}}_{2}$$ during hypoxia and thus contribute to improved hypoxia tolerance. In this study, we used the scanning micro-optrode technique together with quantification of cutaneous vascularity in wild types (WT) and Hif-1α knockouts (hif1aa−/−ab−/−) to test the hypothesis that improved hypoxia tolerance after hypoxia acclimation in larvae at 4 or 7 days post-fertilization (dpf) was associated with Hif-1α-dependent increases in skin vascularity and regional cutaneous O2 fluxes (JO2). Hypoxia tolerance, as determined by measurements of critical PO2 (Pcrit), was unaltered by hypoxia pre-exposure in larvae at 4 dpf and there were no significant differences in Pcrit between WT and hif1aa−/−ab−/− larvae at this developmental stage. However, at 7 dpf there was a significant effect of genotype with WT larvae showing a lower Pcrit than hif1aa−/−ab−/− larvae, an effect that was being driven by a reduced Pcrit in the WT larvae after hypoxia pre-exposure (19.2 ± 1.9 mmHg) compared to hif1aa−/−ab−/− fish (35.5 ± 3.5 mmHg). Regardless of genotype, pre-exposure status or developmental age, JO2 decreased along the body in the anterior-to-posterior direction. Neither hypoxia pre-exposure nor genotype affected JO2 at any region along the body. The lack of any effect of hypoxia pre-exposure or genotype on JO2 was consistent with the lack of any effect on skin vascularity as measured in Tg(fli1:EGFP)yl transgenic larvae. Thus, the decreased hypoxia performance (increased Pcrit) at 7 dpf in the hif1aa−/−ab−/− larvae did not appear to be reliant on changes in trunk vascularity or cutaneous O2 diffusion.

Habitat fragmentation is a principal threat to biodiversity and artificial river barriers are a leading cause of the global decline in freshwater biota. Although the impact of barriers on diadromous fish is well established, impacts on river‐resident fish communities remain unclear, especially for low‐head barriers. We examined the movement of five contrasting freshwater fish (topmouth gudgeon, European minnow, stone loach, bullhead and brown trout) in an experimental cascade mesocosm with seven pools separated by small vertical barriers. Passage rates differed significantly among species and increased with body size and sustained swimming speed ( U sus ), ranging from an average of 0.2 passes/hr in topmouth gudgeon to 3.4 passes/hr in brown trout. A random‐walk simulation indicated that barriers can result in net downstream movement and shifts in community composition. Passage rates in brown trout were leptokurtic, that is, most individuals were relatively sedentary while a small proportion showed frequent movements. Upstream passage rates of brown trout increased with body length and boldness while fish with lower aerobic scope tended to move downstream. Passage rates showed significant individual repeatability in brown trout, independent of body size, indicating the potential for in‐stream barriers to exert selective effects on fish populations. Our results show that barrier effects can be more complex than simply blocking fish passage, and that river‐resident fish can be impacted even by very small barriers. We show that fish passage depends on a wide range of morphological, physiological and behavioural drivers, and that barriers can exert selective effects on these traits and cause shifts in community composition. Policy implications. Barrier mitigation measures need to embrace interspecific and intraspecific variation in fish passage to avoid inadvertent artificial selection on fish communities. Given the high abundance of low‐head structures in river systems worldwide, a paradigm shift is needed to recognise the subtle impacts of small barriers on freshwater biodiversity. Removal of small barriers or nature‐like fishways should allow better passage of the wider fish community compared to widely used salmonid‐centric fish passage options.

Elevated ocean water temperature influences the physiological properties of fishes. This study is expected to characterize the oxygen consumption rate (OCR) and gill morphology in different temperature in hybrid grouper, tiger grouper × giant grouper (TGGGH). TGGGH specimens were distributed into four temperature groups starting from 22, 26, 30 and 34 °C within a recirculatory system under controlled conditions for 30 days in triplicates. Intermittent flow respirometry was directed to distinguish the impact of temperature on the OCR, and scanning electron microscopy was conducted to observe the gill morphology. Results indicated that the OCR of TGGGH increased significantly from 22.98 ± 1.16 mg O 2 h −1 to 37.08 ± 1.56 mg O 2 h −1 when temperature increased from 22 to 34 °C. Values of respired energy (RE) increased from 456.35 ± 11.41 Jh −1 at 22 °C to 737.88 ± 3.79 Jh −1 at 34 °C. Meanwhile, values of temperature quotients ( Q 10 ) were maximum at 22 °C–26 °C and minimum at 26 °C–30 °C. The favored temperature assessed from Q 10 was between 26 °C and 30 °C. Gill lesions were significantly observed at 22 °C and 34 °C. The outcomes proposed that this fish species may neglect to maintain sufficient O 2 uptake in future atmospheric situations. Thus, optimum oxygen consumption is required for maintaining the TGGGH in aquaculture environment.

The behavior of organisms can be subject to human‐induced selection such as that arising from fishing. Angling is expected to induce mortality on fish with bold and explorative behavior, which are behaviors commonly linked to a high standard metabolic rate. We studied the transgenerational response of brown trout ( Salmo trutta ) to angling‐induced selection by examining the behavior and metabolism of 1‐year‐old parr between parents that were or were not captured by experimental fly fishing. We performed the angling selection experiment on both a wild and a captive population, and compared the offspring for standard metabolic rate and behavior under predation risk in common garden conditions. Angling had population‐specific effects on risk taking and exploration tendency, but no effects on standard metabolic rate. Our study adds to the evidence that angling can induce transgenerational responses on fish personality. However, understanding the mechanisms of divergent responses between the populations requires further study on the selectivity of angling in various conditions.

Teneurin C-terminal associated peptides (TCAP), bioactive peptides located on the C-terminal end of teneurin proteins, have been shown to regulate stress axis functions due to the high conservation between TCAP and corticotropin releasing factor (CRF). Additionally, recent work demonstrated that TCAP can increase metabolism in rats via glucose metabolism. These metabolic actions are not well described in other organisms, including teleosts. Here we investigated the expression of a tcap isoform, tcap-3, and the potential role of TCAP-3 as a regulator of metabolism across zebrafish life-stages. Using pcr-based analyses, tcap-3 appears to be independently transcribed, in relation to teneurin-3, in muscle tissue of adult zebrafish. Resazurin, respirometry chambers, and mitochondrial metabolism analyses were used to study the metabolic effects of synthetic rainbow trout TCAP-3 (rtTCAP-3) in larval and adult zebrafish. Overall, metabolic activity was enhanced by 48 h of rtTCAP-3 treatment in larvae (bath immersion) and adults (intraperitoneal injections). This metabolic activity increase was due to mitochondrial uncoupling, as mitochondrial respiration increase by rtTCAP-3 was due to proton leak. Additionally, rtTCAP-3 protected larval fish from reduced metabolic activity induced by low temperatures. Subsequently, rtTCAP-3 increased metabolic output in adult zebrafish subjected to accelerated swimming speeds, demonstrating the potent role of rtTCAP-3 in zebrafish metabolism regulation during metabolic challenges. Collectively, these results demonstrate the conserved roles for rtTCAP-3 as a metabolic activator in zebrafish.

Species-specific ecological traits in fishes are likely to vary between populations or stocks due to differences in regional oceanic conditions, such as latitudinal temperature. We examined potential intraspecific differences in the swimming performance and metabolism of Pacific chub mackerel ( Scomber japonicus ) from the Northwest and Northeast Pacific stocks, which are distributed on opposite sides of the North Pacific at similar latitudes, but where the temperature contrast is large. Swimming bioenergetics and metabolic data of Northwest stock mackerel were measured at 14, 18, and 24°C using variable-speed swim-tunnel respirometers, and then the resulting bioenergetic parameters were compared with previous findings from the Northeast stock. At a given size, the maximum sustainable swimming speed ( U max ) of the Northwest stock showed no significant difference compared to the Northeast stock at 18 and 24°C, but was lower at 14°C. In addition, the oxygen consumption rate ( M O2 ) of the Northwest stock showed lower mass dependence and different temperature dependence at a given swimming speed than in the Northeast stock. Combined with stock-specific data on growth and experienced temperatures in the wild, these bioenergetic differences indicate that the swimming performance and metabolism of the two stocks are specific to their local environment to maximize bioenergetic efficiency.

Three gilthead sea bream families representative of slow, intermediate and fast heritable growth in the Spanish PROGENSA® selection program were used to uncover the effects of such selection on energy partitioning through measurements of fasting weight loss, swimming performance and behavioral traits in one- and two-year-old fish. Firstly, selection for fast growth significantly increased fasting weight loss and decreased the hormonal ratio of circulating Igf-i/Gh in short-term fasting fish (17 days). This is indicative of a stronger negative energy balance that explains the reduced compensatory growth of fast-growing fish during the subsequent short-term refeeding period (7 days). Selection for fast growth also decreased the critical speed (Ucrit, 6–7 BL s−1) at which fish become exhausted in a swim tunnel respirometer. The maximum metabolic rate (MMR), defined as the maximum rate of oxygen consumption during forced exercise, was almost equal in all fish families though the peak was achieved at a lowest speed in the fast-growing family. Since circulating levels of lactate were also slightly decreased in free-swimming fish of this family group, it appears likely that the relative energy contribution of anaerobic metabolism to physical activity was lowered in genetically fast-growing fish. Selection for heritable growth also altered activity behavior because slow-growing families displayed an anticipatory food response associated with more pronounced daily rhythms of physical activity. Also, respiratory frequency and body weight showed and opposite correlation in slow- and fast-growing free-swimming fish as part of the complex trade-offs of growth, behavior and energy metabolism. Altogether, these results indicate that selective breeding for fast growth might limit the anaerobic fitness that would help to cope with limited oxygen availability in a scenario of climate change.

Organismal temperature tolerance and metabolic responses are correlated to recent thermal history, but responses to thermal variability are less frequently assessed. There is great interest in whether organisms that experience greater thermal variability can gain metabolic or tolerance advantages through phenotypic plasticity. We compared thermal tolerance and routine aerobic metabolism of Convict cichlid acclimated for 2 weeks to constant 20 °C, constant 30 °C, or a daily cycle of 20 → 30 °C (1.7 °C/h). Acute routine mass-specific oxygen consumption ( $$\dot{M}$$ O2) and critical thermal maxima/minima (CTMax/CTMin) were compared between groups, with cycle-acclimated fish sampled from the daily minimum (20 °C, 0900 h) and maximum (30 °C, 1600 h). Cycle-acclimated fish demonstrated statistically similar CTMax at the daily minimum and maximum (39.0 °C, 38.6 °C) but distinct CTMin values, with CTMin 2.4 °C higher for fish sampled from the daily 30 °C maximum (14.8 °C) compared to the daily 20 °C minimum (12.4 °C). Measured acutely at 30 °C, $$\dot{M}$$ O2 decreased with increasing acclimation temperature; 20 °C acclimated fish had an 85% higher average $$\dot{M}$$ O2 than 30 °C acclimated fish. Similarly, acute $$\dot{M}$$ O2 at 20 °C was 139% higher in 20 °C acclimated fish compared to 30 °C acclimated fish. Chronic $$\dot{M}$$ O2 was measured in separate fish continually across the 20 → 30 °C daily cycle for all 3 acclimation groups. Chronic $$\dot{M}$$ O2 responses were very similar between groups between average individual hourly values, as temperatures increased or decreased (1.7 °C/h). Acute $$\dot{M}$$ O2 and thermal tolerance responses highlight “classic” trends, but dynamic, chronic trials suggest acclimation history has little effect on the relative change in oxygen consumption during a thermal cycle. Our results strongly suggest that the minimum and maximum temperatures experienced more strongly influence fish physiology, rather than the thermal cycle itself. This research highlights the importance of collecting data in both cycling and static (constant) thermal conditions, and further research should seek to understand whether ectotherm metabolism does respond uniquely to fluctuating temperatures.

Mahi-mahi (Coryphaena hippurus) are a highly migratory pelagic fish, but little is known about what environmental factors drive their broad distribution. This study examined how temperature influences aerobic scope and swimming performance in mahi. Mahi were acclimated to four temperatures spanning their natural range (20, 24, 28, and 32{\deg}C; 5-27 days) and critical swimming speed (Ucrit), metabolic rates, aerobic scope, and optimal swim speed were measured. Aerobic scope and Ucrit were highest in 28{\deg}C-acclimated fish. 20{\deg}C-acclimated mahi experienced significantly decreased aerobic scope and Ucrit relative to 28{\deg}C-acclimated fish (57 and 28% declines, respectively). 32{\deg}C-acclimated mahi experienced increased mortality and a significant 23% decline in Ucrit, and a trend for a 26% decline in factorial aerobic scope relative to 28{\deg}C-acclimated fish. Absolute aerobic scope showed a similar pattern to factorial aerobic scope. Our results are generally in agreement with previously observed distribution patterns for wild fish. Although thermal performance can vary across life stages, the highest tested swim performance and aerobic scope found in the present study (28{\deg}C), aligns with recently observed habitat utilization patterns for wild mahi and could be relevant for climate change predictions.

Oxygen uptake (ṀO2) in larval zebrafish prior to maturation of the gill relies on cutaneous O2 transfer. Under normoxic conditions, rates of cutaneous O2 transfer are unaffected by haemoglobin availability but are diminished in fish lacking a functional circulatory system, suggesting that internal convection is critically involved in setting the resting ṀO2 in zebrafish larvae, even when relying on cutaneous O2 transfer. The reliance of ṀO2 on blood circulation led to the first objective of the current study, to determine whether loss of internal convection would reduce acute hypoxia performance (as determined by measuring critical PO2; Pcrit) in larval zebrafish under conditions of moderate hypoxia (PO2 = 55 mmHg) at 28.5 and 34 °C. Internal convection was eliminated by preventing development of blood vessels using morpholino knockdown of vascular endothelial growth factor (VEGF); these fish are termed VEGF morphants. Breathing frequency (fV) and heart rate (fH) also were measured (at 28.5 °C) to determine whether any detriment in performance might be linked to cardiorespiratory dysfunction. Although ṀO2 was reduced in the VEGF morphants, there was no significant effect on Pcrit at 28.5 °C. Raising temperature to 34 °C resulted in the VEGF morphants exhibiting a higher Pcrit than the shams, suggesting an impairment of hypoxia tolerance in the morphants at the higher temperature. The usual robust increase in fV during hypoxia was absent or attenuated in VEGF morphants at 4 and 5 days post fertilization (dpf), respectively. Resting fH was reduced in the VEGF morphants and unlike the sham fish, the morphants did not exhibit hypoxic tachycardia at 4 or 5 dpf. The number of cutaneous neuroepithelial cells (presumptive O2 chemoreceptors) was significantly higher in the VEGF morphants and thus the cardiorespiratory impairment in the morphants during hypoxia was unlikely related to inadequate peripheral O2 sensing.

This analysis shows good intentions in the selection of valid and precise oxygen uptake ( M ˙ O 2 ) measurements by retaining only slopes of declining dissolved oxygen level in a respirometer that have very high values of the coefficient of determination, r 2, are not always successful at excluding nonlinear slopes. Much worse, by potentially removing linear slopes that have low r 2 only because of a low signal-to-noise ratio, this procedure can overestimate the calculation of standard metabolic rate (SMR) of the fish. To remedy this possibility, a few simple diagnostic tools are demonstrated to assess the appropriateness of a given minimum acceptable r 2, such as calculating the proportion of rejected M ˙ O 2 determinations, producing a histogram of the r 2 values and a plot of r 2 as a function of M ˙ O 2. The authors offer solutions for cases when many linear slopes have low r 2. The least satisfactory but easiest to implement is lowering the minimum acceptable r 2. More satisfactory solutions involve processing (smoothing) the raw signal of dissolved oxygen as a function of time to improve the signal-to-noise ratio and the r 2 s.

Species invasions threaten global biodiversity, and physiological characteristics may determine their impact. Specific dynamic action (SDA; the increase in metabolic rate associated with feeding and digestion) is one such characteristic, strongly influencing an animal's energy budget and feeding ecology. We investigated the relationship between SDA, scope for activity, metabolic phenotype, temperature, and feeding frequency in lionfish (Pterois spp.), an invasive species to western Atlantic marine ecosystems. Intermittent-flow respirometry was used to determine SDA, scope for activity, and metabolic phenotype at 26°C and 32°C. Maximum metabolic rate occurred during digestion, as opposed to exhaustive exercise as in more athletic species. SDA and its duration (SDAdur) was 30% and 45% lower at 32°C than 26°C, respectively, and lionfish ate 42% more at 32°C. Despite a 32% decline in scope for activity from 26°C to 32°C, aerobic scope may have increased by 24%, as there was a higher range between standard metabolic rate (SMR) and peak SDA (the maximum postprandial metabolic rate). Individuals with high SMR and low scope for activity phenotypes had a less costly SDA and shorter SDAdur but a higher SDApeak. Feeding frequently had a lower and more consistent cost than consuming a single meal, but increased SDApeak. These findings demonstrate that: 1) lionfish are robust physiological performers in terms of SDA and possibly aerobic scope at temperatures approaching their thermal maximum, 2) lionfish may consume more prey as oceans warm with climate change, and 3) metabolic phenotype and feeding frequency may be important mediators of feeding ecology in fish.

Availability of shelter is an important component of habitat selection for animals as it can influence survival (protection against harsh physical conditions and predation) and growth (energy acquisition and expenditure). Few studies address the effect of shelter on metabolic expenditures associated to non-mechanical tasks (excluding station holding or movement). The main goal of this study was to investigate the influence of shelter use on metabolic traits of smallmouth bass (Micropterus dolomieu) from two populations (Kiamika River and Lake Long). We conducted respirometry experiments on smallmouth bass to measure standard metabolic rate (SMR), resting metabolic rate (RMR), aerobic scope (AS), recovery time (RT), and excess post-exercise oxygen consumption (EPOC) in presence or in absence of shelter. Presence of shelter did not affect most metabolic traits, except for RMR, which was reduced in presence of shelter for Lake Long fish. Our results also show that larger fish had lower SMR in presence of shelter than when it was absent. When accounting for social hierarchy, there were no differences in most metabolic traits in dominant or subordinate fish in presence or absence of shelter, except for RT, which was significantly lower in presence of shelter for dominant fish. These results do not support the existence of an unequivocal relationship between individual metabolic traits and presence of shelter. If physiological motives may influence the use of shelter, sheltering in itself might not have important consequences on energy expenditures required for non-mechanical tasks. This article is protected by copyright. All rights reserved.

Environment–phenotype interactions are the most pronounced during early life stages and can strongly influence metabolism and ultimately ecological fitness. In the present study, we examined the effect of temperature [ambient river temperature (ART) vs ART+2°C], dissolved oxygen (DO; 100% vs 80%) and substrate (presence vs absence) on standard metabolic rate, forced maximum metabolic rate and metabolic scope with Fulton’s condition factor (K), energy density (ED) and critical thermal maximum (CTmax) in age-0 Lake Sturgeon, Acipenser fulvescens, before and after a simulated overwintering event. We found that all the environmental variables strongly influenced survival, K, ED and CTmax. Fish reared in elevated temperature showed higher mortality and reduced K pre-winter at 127 days post-hatch (dph). Interestingly, we did not find any significant difference in terms of metabolic rate between treatments at both sampling points of pre- and post-winter. Long-term exposure to 80% DO reduced ED in Lake Sturgeon post-winter at 272 dph. Our data suggest that substrate should be removed at the onset of exogenous feeding to enhance the survival rate of age-0 Lake Sturgeon in the first year of life. Effects of early rearing environment during larval development on survival over winter are discussed with respect to successful recruitment of stock enhanced Lake Sturgeon, a species that is at risk throughout its natural range.

As a crucial step in developing a bioenergetics model for Pacific Chub Mackerel Scomber japonicus (hereafter chub mackerel), parameters related to metabolism, the largest dissipation term in bioenergetics modelling, were estimated. Swimming energetics and metabolic data for nine chub mackerel were collected at 14°C, a low temperature within the typical thermal range of this species, using variable‐speed swim‐tunnel respirometry. These new data were combined with previous speed‐dependent metabolic data at 18 and 24°C and single‐speed (1 fork length per second: FL/s ) metabolic data at 15 and 20°C to estimate respiration parameters for model development. Based on the combined data, the optimal swimming speed (the swimming speed with the minimum cost of transport, U opt ) was 42.5 cm/s (1.5–3.0 FL/s or 2.1 ± 0.4 FL/s ) and showed no significant dependence on temperature or fish size. The daily mass‐specific oxygen consumption rate ( R, g O 2 g fish −1 day −1 ) was expressed as a function of fish mass ( W ), temperature ( T ) and swimming speed ( U ): R = 0.0103 W −0.490 e (0.0457 T ) e (0.0235 U ). Compared to other small pelagic fishes such as Pacific Herring Clupea harengus pallasii, Pacific Sardine Sardinops sagax and various anchovy species, chub mackerel respiration showed a lower dependence on fish mass, temperature and swimming speed, suggesting a greater swimming ability and lower sensitivity to environmental temperature variation.

We investigated the effects of seawater warming and CO2 enrichment on the microbial community metabolism (using O2 consumption as a proxy) in subtidal silt sediment. Intact sediment cores, without large dwelling infauna, were incubated for 24 days at 12 (in situ) and 18 °C to confirm the expected temperature response. We then enriched the seawater overlying a subset of cold and warm-incubated cores with CO2 (+ ΔpCO2: 253–396 µatm) for 16 days and measured the metabolic response. Warming increased the depth-integrated volume-specific O2 consumption (Rvol), the maximum in the volume-specific O2 consumption at the bottom of the oxic zone (Rvol,bmax) and the volume-specific net O2 production (Pn,vol), and decreased the O2 penetration depth (O2-pd) and the depth of Rvol,bmax (depthbmax). Benthic photosynthesis oscillated the pH in the upper 2 mm of the sediment. CO2 enrichment of the warm seawater did not alter this oscillation but shifted the pH profile towards acidity; the effect was greatest at the surface and decreased to a depth of 12 mm. Confoundment rendered the CO2 treatment of the cold seawater inconclusive. In warm seawater, we found no statistically clear effect of CO2 enrichment on Rvol, Rvol,bmax, Pn,vol, O2-pd, or depthbmax and therefore suspect that this perturbation did not alter the microbial community metabolism. This confirms the conclusion from experiments with other, contrasting types of sediment.

Fishes living in fresh water counter the passive loss of salts by actively absorbing ions through specialized cells termed ionocytes. Ionocytes contain ATP-dependent transporters, are enriched with mitochondria, and therefore ionic regulation is an energy-consuming process. The purpose of this study was to assess the aerobic costs of ion transport in larval zebrafish (Danio rerio). We hypothesized that changes in rates of Na+ uptake evoked by acidic or low Na+ rearing conditions would result in corresponding changes in whole-body oxygen consumption (ṀO2) and/or cutaneous oxygen flux (JO2), measured at the ionocyte-expressing yolk sac epithelium using the scanning micro-optrode technique (SMOT). Larvae at 4 days post-fertilisation (dpf) that were reared under low pH (pH 4) exhibited a higher rate of Na+ uptake compared to fish reared under control conditions (pH 7.6) yet displayed a lower ṀO2 and no difference in cutaneous JO2. Despite a higher Na+ uptake capacity in larvae reared under low Na+ conditions, there were no differences in ṀO2 ­and JO2 at 4 dpf. Furthermore, although Na+ uptake was nearly abolished in 2 dpf larvae lacking ionocytes after morpholino knockdown of the ionocyte proliferation regulating transcription factor foxi3a, ṀO2 ­and JO2 were unaffected. Finally, laser ablation of ionocytes did not affect cutaneous JO2. Thus, we conclude that the aerobic costs of ion uptake by ionocytes in larval zebrafish, at least in the case of Na+, are below detection using whole-body respirometry or cutaneous SMOT scans, providing evidence that ion regulation in zebrafish larvae incurs a low aerobic cost.

Juvenile striped bass reside in the Chesapeake Bay where they are likely to encounter hypoxia that could affect their metabolism and performance. The ecological success of this economically valuable species may depend on their ability to tolerate hypoxia and perform fitness-dependent activities in hypoxic waters. We tested whether there is a link between hypoxia tolerance (HT) and oxygen consumption rate (ṀO2) of juvenile striped bass measured while swimming in normoxic and hypoxic water, and to identify the interindividual variation and repeatability of these measurements. Fish (N=18) had their HT (loss of equilibrium) measured twice collectively, 11 weeks apart, between which each fish had their ṀO2 measured individually while swimming in low flow (10.2 cm s−1) and high flow (∼ 67% Ucrit) under normoxia and hypoxia. Both HT and ṀO2 varied substantially among individuals. HT increased across 11 weeks while the rank order of individual HT was significantly repeatable. Similarly, ṀO2 increased in fish swimming at high flow in a repeatable fashion, but only within a given level of oxygenation. ṀO2 was significantly lower when fish were swimming against high flow under hypoxia. There were no clear relationships between HT and a fish's ṀO2 while swimming under any conditions. Only the magnitude of increase in HT over 11 weeks and an individual's ṀO2 under low flow were correlated. The results suggest that responses to the interacting stressors of hypoxia and exercise vary among individuals, and that HT and change in HT are not simple functions of aerobic metabolic rate.

Environmental conditions during early life can have a profound impact on developmental trajectory and ultimately ecological fitness of individuals. Therefore, from a conservation perspective it is vital to understand the longer-term implications of early phenotypic development on survival. In this study, we examined the effects of temperature (maintained at 16°C or ambient river temperature), prey condition (live or dead Artemia) and incubation method (tumbling jar or natural hatching over substrate) on the routine or standard metabolic rate (RMR, SMR), maximum metabolic rate (MMR), factorial aerobic scope, energy density (ED), whole body triglyceride concentration (TG), growth and mortality rate of age-0 lake sturgeon. Our results demonstrated that fish fed live artemia had significantly lower ED, growth and high mortality rates than those fed dead artemia at 32 days post-fertilisation (dpf) (p <.001). However, at 133 dpf fish fed live artemia showed higher MMR and no difference in ED, TG and growth rate compared to those fed dead prey during early life history. The present study showed that inclusion of live prey at the onset of exogenous feeding may be considered to promote a more natural phenotypic development in larval lake sturgeon.

Plastic polymers have quickly become one of the most abundant materials on Earth due to their low production cost and high versatility. Unfortunately, some of the discarded plastic can make its way into the environment and become fragmented into smaller microscopic particles, termed secondary microplastics (MP). In addition, primary MP, purposely manufactured microscopic plastic particles, can also make their way into our environment via various routes. Owing to their size and resilience, these MP can then be easily ingested by living organisms. The effect of MP particles on living organisms is suspected to have negative implications, especially during early development. In this study, we examined the effects of polyethylene MP ingestion for four and ten days of exposure starting at 5 days post-fertilization (dpf). In particular, we examined the effects of polyethylene MP exposure on resting metabolic rate, on gene expression of several inflammatory and oxidative stress linked genes, and on microbiome composition between treatments. Overall, we found no evidence of broad metabolic disturbances or inflammatory markers in MP-exposed fish for either period of time. However, there was a significant increase in the oxidative stress mediator L-FABP that occurred at 15 dpf. Furthermore, the microbiome was disrupted by MP exposure, with evidence of an increased abundance of Bacteroidetes in MP fish, a combination frequently found in intestinal pathologies. Thus, it appears that acute polyethylene MP exposure can increase oxidative stress and dysbiosis, which may render the animal more susceptible to diseases.

Establishing relationships between parasite infection and physiological condition of the host can be difficult and therefore are often neglected when describing factors causing population declines. Using the parasite–host system between the parasitic nematode Contracaecum osculatum and the Eastern Baltic cod Gadus morhua, we here shed new light on how parasite load may relate to the physiological condition of a transport host. The Eastern Baltic cod is in distress, with declining nutritional conditions, disappearance of the larger fish, high natural mortality and no signs of recovery of the population. During the latest decade, high infection levels with C. osculatum have been observed in fish in the central and southern parts of the Baltic Sea. We investigated the aerobic performance, nutritional condition, organ masses, and plasma and proximate body composition of wild naturally infected G. morhua in relation to infection density with C. osculatum. Fish with high infection densities of C. osculatum had (i) decreased nutritional condition, (ii) depressed energy turnover as evidenced by reduced standard metabolic rate, (iii) reduction in the digestive organ masses, and alongside (iv) changes in the plasma, body and liver composition, and fish energy source. The significantly reduced albumin to globulin ratio in highly infected G. morhua suggests that the fish suffer from a chronic liver disease. Furthermore, fish with high infection loads had the lowest Fulton’s condition factor. Yet, it remains unknown whether our results steam from a direct effect of C. osculatum, or because G. morhua in an already compromised nutritional state are more susceptible towards the parasite. Nevertheless, impairment of the physiological condition can lead to reduced swimming performance, compromising foraging success while augmenting the risk of predation, potentially leading to an increase in the natural mortality of the host. We hence argue that fish–parasite interactions must not be neglected when implementing and refining strategies to rebuild deteriorating populations.

To forage in fast, turbulent flow environments where prey is abundant, fishes must deal with the high associated costs of locomotion. Prevailing theory suggests that many species exploit hydrodynamic refuges to minimize the cost of locomotion while foraging. Here, we challenge this theory based on direct oxygen consumption measurements of drift-feeding trout (Oncorhynchus mykiss) foraging in the freestream and from behind a flow refuge at velocities up to 100 cm s−1. We demonstrate that refuging is not energetically beneficial when foraging in fast flows because of a high attack cost and low prey capture success associated with leaving a station-holding refuge to intercept prey. By integrating optimum foraging theory with empirical data from respirometry and video tracking, we developed a mathematical model to predict when drift-feeding fishes should exploit or avoid refuges based on prey density, size and flow velocity. Our optimum foraging and refuging model provides new mechanistic insights into locomotor costs, habitat use and prey choice of fish foraging in current-swept habitats.

Ocean acidification is occurring in conjunction with warming and deoxygenation as a result of anthropogenic greenhouse gas emissions. Multistressor experiments are critically needed to better understand the sensitivity of marine organisms to these concurrent changes. Growth and survival responses to acidification have been documented for many marine species, but studies that explore underlying physiological mechanisms of carbon dioxide (CO2) sensitivity are less common. We investigated oxygen consumption rates as proxies for metabolic responses in embryos and newly hatched larvae of an estuarine forage fish (Atlantic silverside, Menidia menidia) to factorial combinations of CO2×temperature or CO2×oxygen. Metabolic rates of embryos and larvae significantly increased with temperature, but partial pressure of CO2 (PCO2) alone did not affect metabolic rates in any experiment. However, there was a significant interaction between PCO2 and partial pressure of oxygen (PO2) in embryos, because metabolic rates were unaffected by PO2 level at ambient PCO2, but decreased with declining PO2 under elevated PCO2. For larvae, however, PCO2 and PO2 had no significant effect on metabolic rates. Our findings suggest high individual variability in metabolic responses to high PCO2, perhaps due to parental effects and time of spawning. We conclude that early life metabolism is largely resilient to elevated PCO2 in this species, but that acidification likely influences energetic responses and thus vulnerability to hypoxia.

Publicly available toxicological studies on wastewaters associated with unconventional oil and gas (UOG) activities in offshore regions are nonexistent. The current study investigated the impact of hydraulic fracturing-generated flowback water (HF-FW) on whole organism swimming performance/respiration and cardiomyocyte contractility dynamics in mahi-mahi ( Coryphaena hippurus -hereafter referred to as "mahi"), an organism which inhabits marine ecosystems where offshore hydraulic fracturing activity is intensifying. Following exposure to 2.75% HF-FW for 24 h, mahi displayed significantly reduced critical swimming speeds ( U crit ) and aerobic scopes (reductions of ∼40 and 61%, respectively) compared to control fish. Additionally, cardiomyocyte exposures to the same HF-FW sample at 2% dilutions reduced a multitude of mahi sarcomere contraction properties at various stimulation frequencies compared to all other treatment groups, including an approximate 40% decrease in sarcomere contraction size and a nearly 50% reduction in sarcomere relaxation velocity compared to controls. An approximate 8-fold change in expression of the cardiac contractile regulatory gene cmlc2 was also seen in ventricles from 2.75% HF-FW-exposed mahi. These results collectively identify cardiac function as a target for HF-FW toxicity and provide some of the first published data on UOG toxicity in a marine species.

The aim of this study was to investigate swimming performance and oxygen consumption as non‐lethal indicator traits of production parameters in Atlantic salmon Salmo salar L. and Gilthead seabream Sparus aurata L. A total of 34 individual fish of each species were subjected to a series of experiments: 1) a critical swimming speed (Ucrit) test in a swim-gutter, followed by 2) two starvation-refeeding periods of 42 days, and 3) swimming performance experiments coupled to respirometry in swim-tunnels. Ucrit was assessed first to test it as a predictor trait. Starvation-refeeding traits included body weight; feed conversion ratio based on dry matter; residual feed intake; average daily weight gain and loss. Swim-tunnel respirometry provided oxygen consumption in rest and while swimming at the different speeds, optimal swim speed and minimal cost of transport. After experiments, fish were dissected and measured for tissue weights and body composition in terms of dry matter, ash, fat, protein and moist, and energy content. The Ucrit test design was able to provide individual Ucrit values in high throughput manner. The residual Ucrit (RUcrit) should be considered in order to remove the size dependency of swimming performance. Most importantly, RUcrit predicted fillet yield in both species. The minimal cost of transport, the oxygen consumption when swimming at Uopt, added predictive value to the seabream model for feed intake.

Feed withdrawal is a widespread practice in Atlantic salmon (Salmo salar) aquaculture to empty the gut prior to major farming operations, while certain pathogens and suboptimal environmental conditions in production cages are known to induce prolonged fasting. However, these fasting periods may be in conflict with ethical and legal obligations to farm animals. Presently, science-based recommendations on responsible fasting times that consider fish welfare are lacking. In this study, we measured the standard metabolic rate (SMR) and metabolic rate following acute handling and confinement stress in Atlantic salmon post smolts (~575 g, ~38 cm) following 1, 2, 3 and 4 weeks of feed withdrawal and 1 week of subsequent refeeding at 12 °C. The purpose was to identify when changes in metabolic mode occurred and assess whether the capacity to respond to stress eventually was compromised, since such observations could serve as potential welfare indicators. The SMR decreased significantly from 84.4 ± 4.7 mg O2 kg h−1 in control fish to 71.0 ± 1.8 mg O2 kg h−1 following 1 week of fasting. A further significant decrease to 65.0 ± 3.7 mg O2 kg h−1 was measured after 3 weeks, while refeeding returned SMR to control levels. The increase in MO2 following acute stress was unaffected for the first three weeks of fasting. However, the 4 week group showed a reduced peak response compared to the preceding weeks (278 ± 13 vs. 310 ± 7 mg O2 kg h−1). Weight, fork length and condition factor did not change significantly during the fasting period, and the fish immediately resumed eating upon refeeding. We conclude that up to 4 weeks of feed withdrawal had negligible effects on fish welfare. Moreover, an improved aerobic scope owing to a reduced SMR may be advantageous prior to certain farm operations.

Pace-of-life syndromes (POLS) describe covariations between life history (such as growth rate and age at maturity), behaviour (e.g. activity or boldness) and physiology (e.g. metabolic rate) along an axis from fast to slow lifestyles. This powerful concept can be applicable at a range of scales, from broad interspecific contrasts to the individual intra-population level, though its generality has recently been questioned. Using two species of African annual fishes with fast lifestyles, we tested how individual-level POLS covary between the sexes and contrasting social environments. Measuring three key metabolic parameters (standard metabolic rate, SMR; maximum metabolic rate, MMR; and aerobic scope, AS), we found extensive variation between species and sexes in the expression of POLS. Social environment affected individual metabolic traits, but not their covariation with behaviour and life history traits. In accordance with the POLS prediction, we observed a positive association between MMR, AS and boldness, and a negative association between MMR, AS and lifespan in Nothobranchius orthonotus males, although trait covariations were opposite in N. orthonotus females. In Nothobranchius pienaari, we confirmed the predicted negative correlation between SMR and lifespan which was not sex-specific. Contrary to POLS predictions, we observed a negative correlation between SMR and boldness in N. pienaari. Finally, there was no link between activity levels or size at maturity and metabolic traits in either species. Overall, we demonstrated limited support for POLS predictions, but found that specific pace-of-life trait associations were mediated by both interspecific and intersexual differences.

The establishment of the piscivorous lionfish Pterois spp. in the Western Atlantic and wider Caribbean is a well-documented example of a successful marine invasion. Recently, lionfish have been shown to colonise a wide range of ecosystems and tolerate a wider range of salinities than previously thought. In the present study, lionfish were maintained in aquaria under differing salinity treatments (10, 20 and 37 psu) similar to those they might experience in an estuarine ecosystem. The effects of long-term hyposaline exposure on growth, metabolic rate, maximum food consumption and digestion were examined. Consistent with previous studies, lionfish were able to survive in hyposaline conditions for extended periods of time. However, lionfish in the most hyposaline treatment (10 psu) exhibited reduced growth under low food conditions, lower maximum metabolic rate, lower aerobic scope, lower maximum food consumption, took longer to digest a standardized meal size and occupied a greater percentage of their aerobic scope during digestion. Results suggest that (1) given the ability of lionfish to tolerate low salinity, updated range expansion models should incorporate salinity data to improve accuracy of predicted range expansion and (2) the invasion of lionfish into low salinity ecosystems, although a serious concern, will not likely lead to the same level of population increase observed for coral reef habitats due to the physiological costs associated with living in low salinities.

Physiological features of species can determine the resilience and adaptation of organisms to the environment. Swimming capacity and metabolic traits are key factors for fish survival, mating and predator–prey interactions. Individuals of the same species can display high phenotypic variation often in response to varying environmental conditions. We investigated the effects of captive breeding conditions on swimming capacity, metabolic traits and morphology by comparing a captive population with a wild population of the endangered Spanish toothcarp (Aphanius iberus). We measured swimming capabilities and oxygen‐uptake rates simultaneously, the latter as a proxy for metabolic rate, using a swim tunnel respirometer. Results showed significant differences in standard metabolic rate (SMR), maximum metabolic rate (MMR) and absolute aerobic scope (AAS) between populations, as well as differences in morphological features between populations and sexes. In contrast, we did not find significant differences in critical swimming speed between populations or sexes. Differences in SMR between sexes were found in the captive population, and males showed nearly a twofold increase in SMR when compared with females. SMR, MMR and AAS were, on average, twofold lower for the captive population in comparison with the wild population. These differences in metabolic traits likely reflected captivity conditions, which were low food availability and the absence of predators, which in turn, may have influenced morphological traits, such as body and caudal peduncle shape and head size. At the same time, morphological traits also influenced metabolic traits of the populations. The lower SMR and MMR of captive individuals may be related to their deeper body shapes. Taken together, our results suggested that captive breeding conditions caused significant physiological and morphological changes in the endangered Spanish toothcarp. Reduced metabolic traits and changes in morphology may affect fitness‐related traits of the captive populations once reintroduced into the wild, thereby compromising conservation efforts. We therefore recommend to experimentally testing for the effects and consequences of captive breeding conditions

We tested whether thermal tolerance and aerobic performance differed between two populations of Nile perch (Lates niloticus) originating from the same source population six decades after their introduction into two lakes in the Lake Victoria basin in East Africa. We used short-term acclimation of juvenile fish to a range of temperatures from ambient to +6o C, and performed critical thermal maximum (CTmax ) and respirometry tests to measure upper thermal tolerance, resting and maximum metabolic rates (RMR and MMR), and aerobic scope (AS). Across acclimation temperatures, Nile perch from the cooler lake (Lake Nabugabo, Uganda) tended to have lower thermal tolerance (i.e., CTmax ) and lower aerobic performance (i.e., aerobic scope; AS) than Nile perch from the warmer waters of Lake Victoria (Bugonga region, Uganda). Effects of temperature acclimation were more pronounced in the Lake Victoria population, with the Lake Nabugabo fish showing less thermal plasticity in most metabolic traits. Our results suggest phenotypic divergence in thermal tolerance between these two introduced populations in a direction consistent with an adaptive response to local thermal regimes. This article is protected by copyright. All rights reserved.

Forecasts from climate models and oceanographic observations indicate increasing deoxygenation in the global oceans and an elevated frequency and intensity of hypoxic events in the coastal zone, which have the potential to affect marine biodiversity and fisheries. Exposure to low dissolved oxygen (DO) conditions may have deleterious effects on early life stages in fishes. This study aims to identify thresholds to hypoxia while testing behavioral and physiological responses of two congeneric species of kelp forest fish to four DO levels, ranging from normoxic to hypoxic (8.7, 6.0, 4.1, and 2.2 mg O 2 /L). Behavioral tests identified changes in exploratory behavior and turning bias (lateralization), whereas physiological tests focused on determining changes in hypoxia tolerance (pCrit), ventilation rates, and metabolic rates, with impacts on the resulting capacity for aerobic activity. Our findings indicated that copper rockfish ( Sebastes caurinus ) and blue rockfish ( Sebastes mystinus ) express sensitivity to hypoxia; however, the strength of the response differed between species. Copper rockfish exhibited reduced absolute lateralization and increased escape time at the lowest DO levels, whereas behavioral metrics for blue rockfish did not vary with oxygen level. Both species exhibited decreases in aerobic scope (as a function of reduced maximum metabolic rate) and increases in ventilation rates to compensate for decreasing oxygen levels. Blue rockfish had a lower pCrit and stronger acclimation response compared to copper rockfish. The differences expressed by each species suggest that acclimatization to changing ocean conditions may vary, even among related species that recruit to the same kelp forest habitat, leading to winners and losers under future ocean conditions. Exposure to hypoxia can decrease individual physiological fitness through metabolic and aerobic depression and changes to anti‐predator behavior, with implications for the outcome of ecological interactions and the management of fish stocks in the face of climate change.

Indo-Pacific lionfish (Pterois spp.) have become established throughout the Caribbean and the coastal regions of the Gulf of Mexico and western Atlantic Ocean from North Carolina to central Brazil. Lionfish may also invade estuaries, as they tolerate salinities down to 4‰. We hypothesize that the functional characteristics of their visual system (which evolved in the clear tropical waters of the Indo-Pacific) or their inability to tolerate hypoxia will limit the capacity of lionfish to occupy these areas. We assessed the former with corneal electroretinography and the latter with intermittent-flow respirometry. The luminous sensitivity, temporal resolution (quantified as flicker fusion frequency), and spectral sensitivity of the lionfish visual system are like those of native piscivores, indicating that their visual system will be functional under estuarine photic conditions and allow lionfish to be effective piscivores. In contrast, acute exposure to reduced oxygen levels (equivalent to those commonly occurring in mid-Atlantic and Gulf of Mexico estuaries) exceeded the physiological tolerances of lionfish. We therefore conclude that hypoxia will control or limit estuarine invasion.

Energy metabolism fuels swimming and other biological processes. We compared the swimming performance and energy metabolism within and across eight freshwater fish species. Using swim tunnel respirometers, we measured the standard metabolic rate (SMR) and maximum metabolic rate (MMR) and calculated the critical swimming speed (Ucrit). We accounted for body size, metabolic traits, and some morphometric ratios in an effort to understand the extent and underlying causes of variation. Body mass was largely the best predictor of swimming capacity and metabolic traits within species. Moreover, we found that predictive models using total length or SMR, in addition to body mass, significantly increased the explained variation of Ucrit and MMR in certain fish species. These predictive models also underlined that, once body mass has been accounted for, Ucrit can be independently affected by total length or MMR. This study exemplifies the utility of multiple regression models to assess within-species variability. At interspecific level, our results showed that variation in Ucrit can partly be explained by the variation in the interrelated traits of MMR, fineness, and muscle ratios. Among the species studied, bleak Alburnus alburnus performed best in terms of swimming performance and efficiency. By contrast, pumpkinseed Lepomis gibbosus showed very poor swimming performance, but attained lower mass-specific cost of transport (MCOT) than some rheophilic species, possibly reflecting a cost reduction strategy to compensate for hydrodynamic disadvantages. In conclusion, this study provides insight into the key factors influencing the swimming performance of fish at both intra- and interspecific levels.

Typically, laboratory studies on the physiological effects of temperature are conducted using stable acclimation temperatures. However, information extrapolated from these studies may not accurately represent wild populations living in thermally variable environments. Our objective was to compare the growth, metabolism, and swimming performance of wild Atlantic salmon exposed to cycling 16-21o C, and stable 16o C, 18.5o C, 21o C acclimation temperatures. Growth rate, metabolic rate, swimming performance, and anaerobic metabolites did not change among acclimation groups, suggesting that within Atlantic salmon's thermal optimum range, temperature variation has no effect on these physiological properties. This article is protected by copyright. All rights reserved.

The ability of organisms to cope with environmental stressors depends on the duration and intensity of the stressor, as well as the type of stress. For aquatic organisms, oxygen limitation has been implicated in limiting heat tolerance. Here we examine how starvation affects heat tolerance in the amphipod Gammarus fossarum (Koch, 1836) and whether observed changes can be explained from alterations in oxidative metabolism, depletion of energy reserves, upregulation of heat shock proteins or susceptibility to oxygen limitation. Starved amphipods showed impaired survival compared to fed amphipods during prolonged exposure to mild heat. In contrast, under acute, high-intensity heat exposure they actually showed improved survival. We observed a lower demand for oxygen in starved amphipods which could make them less susceptible to oxygen limitation. Such a role for oxygen in limiting heat tolerance was verified as hypoxia impaired the heat tolerance of amphipods, especially starved ones. Fed amphipods likely rely more on anaerobic metabolism to maintain energy status during heat stress, whereas for starved amphipods aerobic metabolism appears to be more important. The depletion of their energy reserves constrains their ability to maintain energy status via anaerobic metabolism. We did not find evidence that alterations in heat tolerance following starvation were related to the upregulation of heat shock proteins. In conclusion, starvation can have opposite effects on heat tolerance, acting via pathways that are operating on different time scales.

This study hypothesized that oxygen uptake ( Ṁ O 2 ) measured with a novel protocol of chasing rainbow trout Oncorhynchus mykiss to exhaustion inside a static respirometer while simultaneously monitoring Ṁ O 2 ( Ṁ O 2chase ) would generate the same and repeatable peak value as when peak active Ṁ O 2 ( Ṁ O 2active ) is measured in a critical swimming speed protocol. To reliably determine peak Ṁ O 2chase, and compare to the peak during recovery of Ṁ O 2 after a conventional chase protocol outside the respirometer ( Ṁ O 2rec ), this study applied an iterative algorithm and a minimum sampling window duration ( i.e., 1 min based on an analysis of the variance in background and exercise Ṁ O 2 ) to account for Ṁ O 2 dynamics. In support of this hypothesis, peak Ṁ O 2active (707 ± 33 mg O 2 h −1 kg −1 ) and peak Ṁ O 2chase (663 ± 43 mg O 2 h −1 kg −1 ) were similar ( P = 0.49) and repeatable (Pearson's and Spearman's correlation test; r ≥ 0.77; P < 0.05) when measured in the same fish. Therefore, estimates of Ṁ O 2max can be independent of whether a fish is exhaustively chased inside a respirometer or swum to fatigue in a swim tunnel, provided Ṁ O 2 is analysed with an iterative algorithm and a minimum but reliable sampling window. The importance of using this analytical approach was illustrated by peak Ṁ O 2chase being 23% higher ( P < 0.05) when compared with a conventional sequential interval regression analysis, whereas using the conventional chase protocol (1‐min window) outside the respirometer increased this difference to 31% ( P < 0.01). Moreover, because peak Ṁ O 2chase was 18% higher ( P < 0.05) than peak Ṁ O 2rec, chasing a fish inside a static respirometer may be a better protocol for obtaining maximum Ṁ O 2.

Extensions of species’ geographical distributions, or range extensions, are among the primary ecological responses to climate change in the oceans. Considerable variation across the rates at which species’ ranges change with temperature hinders our ability to forecast range extensions based on climate data alone. To better manage the consequences of ongoing and future range extensions for global marine biodiversity, more information is needed on the biological mechanisms that link temperatures to range limits. This is especially important at understudied, low relative temperatures relevant to poleward range extensions, which appear to outpace warm range edge contractions four times over. Here, we capitalized on the ongoing range extension of a teleost predator, the Australasian snapper Chrysophrys auratus, to examine multiple measures of ecologically relevant physiological performance at the population’s poleward range extension front. Swim tunnel respirometry was used to determine how mid-range and poleward range edge winter acclimation temperatures affect metabolic rate, aerobic scope, swimming performance and efficiency and recovery from exercise. Relative to ‘optimal’ mid-range temperature acclimation, subsequent range edge minimum temperature acclimation resulted in absolute aerobic scope decreasing while factorial aerobic scope increased; efficiency of swimming increased while maximum sustainable swimming speed decreased; and recovery from exercise required a longer duration despite lower oxygen payback. Cold-acclimated swimming faster than 0.9 body lengths sec−1 required a greater proportion of aerobic scope despite decreased cost of transport. Reduced aerobic scope did not account for declines in recovery and lower maximum sustainable swimming speed. These results suggest that while performances decline at range edge minimum temperatures, cold-acclimated snapper are optimized for energy savings and range edge limitation may arise from suboptimal temperature exposure throughout the year rather than acute minimum temperature exposure. We propose incorporating performance data with in situ behaviour and environmental data in bioenergetic models to better understand how thermal tolerance determines range limits.

Estrogenic endocrine disrupting compounds (EEDCs), such as ethinylestradiol (EE2), are well studied for their impact on the reproductive system of fish. EEDCs may also impact the immune system and, as a consequence, the disease susceptibility of fish. It is currently not yet known whether the low concentrations of EEDCs that are able to disrupt the reproductive system of trout are effective in disrupting the immune system and the fish host resistance towards pathogens, too, or whether such immunodisruptive effects would occur only at higher EEDC concentrations. Therefore, in the present study we compare the effect thresholds of low 17α-ethinylestradiol concentrations (1.5 and 5.5 EE2 ng/L) on the reproductive system, the immune system, the energy expenditures and the resistance of juvenile rainbow trout (Oncorhynchus mykiss) against the parasite Tetracapsuloides bryosalmonae - the etiological agent of proliferative kidney disease (PKD) of salmonids. The parasite infection was conducted without injection and under low pathogen exposure concentrations. The disease development was followed over 130 days post infection - in the presence or absence of EE2 exposure. The results show that the long-term EE2 exposure affected, at both concentrations, reproductive parameters like the mRNA levels of hepatic vitellogenin and estrogen receptors. At the same concentrations, EE2 exposure modulated the immune parameters: mRNA levels of several immune genes were altered and the parasite intensity as well as the disease severity (histopathology) were significantly reduced in EE2-exposed fish compared to infected control fish. The combination of EE2 exposure and parasite infection was energetically costly, as indicated by the decreased values of the swim tunnel respirometry. Although further substantiation is needed, our findings suggest that EE2 exerts endocrine disruptive and immunomodulating activities at comparable effect thresholds, since reproductive and immune parameters were affected by the same, low EE2 concentrations.

Metabolism is linked with the pace-of-life, co-varying with survival, growth, and reproduction. Metabolic rates should therefore be under strong selection and, if heritable, become less variable over time. Yet intraspecific variation in metabolic rates is ubiquitous, even after accounting for body mass and temperature. Theory predicts variable selection maintains trait variation, but field estimates of how selection on metabolism varies are rare. We use a model marine invertebrate to estimate selection on metabolic rates in the wild under different competitive environments. Fitness landscapes varied among environments separated by a few centimeters: interspecific competition selected for higher metabolism, and a faster pace-of-life, relative to competition-free environments. Populations experience a mosaic of competitive regimes; we find metabolism mediates a competition-colonization trade-off across these regimes. Although high metabolic phenotypes possess greater competitive ability, in the absence of competitors, low metabolic phenotypes are better colonizers. Spatial heterogeneity and the variable selection on metabolic rates that it generates is likely to maintain variation in metabolic rate, despite strong selection in any single environment.

The coordination of the hypoxic response is attributed, in part, to hypoxia-inducible factor 1α (Hif-1α), a regulator of hypoxia-induced transcription. After the teleost-specific genome duplication, most teleost fishes lost the duplicate copy of Hif-1α, except species in the cyprinid lineage that retained both paralogues of Hif-1α (Hif1aa and Hif1ab). Little is known about the contribution of Hif-1α, and specifically of each paralogue, to hypoxia tolerance. Here, we examined hypoxia tolerance in wild-type (Hif1aa +/+ ab +/+ ) and Hif-1α knockout lines (Hif1aa −/−; Hif1ab −/−; Hif1aa −/− ab −/− ) of zebrafish ( Danio rerio ). Critical O 2 tension ( P crit; the partial pressure of oxygen (PO 2 ) at which O 2 consumption can no longer be maintained) and time to loss of equilibrium (LOE), two indices of hypoxia tolerance, were assessed in larvae and adults. Knockout of both paralogues significantly increased P crit (decreased hypoxia tolerance) in larval fish. Prior exposure of larvae to hypoxia decreased P crit in wild-type fish, an effect mediated by the Hif1aa paralogue. In adults, individuals with a knockout of either paralogue exhibited significantly decreased time to LOE but no difference in P crit. Together, these results demonstrate that in zebrafish, tolerance to hypoxia and improved hypoxia tolerance after pre-exposure to hypoxia (pre-conditioning) are mediated, at least in part, by Hif-1α.

Ectothermic animals are especially susceptible to temperature change, considering that their metabolism and core temperature are linked to the environmental temperature. As global water temperatures continue to increase, so does the need to understand the capacity of organisms to tolerate change. Sheepshead minnows (Cyprinodon variegatus) are the most eurythermic fish species known to date and can tolerate a wide range of environmental temperatures from − 1.9 to 43.0 °C. But little is known about the physiological adjustments that occur when these fish are subjected to acute thermal challenges and long-term thermal acclimation. Minnows were acclimated to 10, 21, or 32 °C for 4 weeks or acutely exposed to 10 and 32 °C and then assessed for swimming performance [maximum sustained swimming velocity (Ucrit), optimum swimming velocity (Uopt)] and metabolic endpoints (extrapolated standard and maximum metabolic rate [SMR, MMR), absolute aerobic scope (AS), and cost of transport (COT)]. Our findings show that the duration of thermal exposure (acute vs. acclimation) did not influence swimming performance. Rather, swimming performance was influenced by the exposure temperature. Swimming performance was statistically similar in fish exposed to 21 or 32 °C (approximately 7.0 BL s−1), but was drastically reduced in fish exposed to 10 °C (approximately 2.0 BL s−1), resulting in a left-skewed performance curve. There was no difference in metabolic end points between fish acutely exposed or acclimated to 10 °C. However, a different pattern was observed in fish exposed to 32 °C. MMR was similar between acutely exposed or acclimated fish, but acclimated fish had a 50% reduction in extrapolated SMR, which increased AS by 25%. However, this enhanced AS was not associated with changes in swimming performance, which opposes the oxygen-capacity limited thermal tolerance concept. Our findings suggest that sheepshead minnows may utilize two distinct acclimation strategies, resulting in different swimming performance and metabolic patterns observed between 10 and 32 °C exposures.

Experimental biologists now routinely quantify maximum metabolic rate (MMR) in fishes using respirometry, often with the goal of calculating aerobic scope and answering important ecological and evolutionary questions. Methods used for estimating MMR vary considerably, with the two most common methods being (i) the ‘chase method’, where fish are manually chased to exhaustion and immediately sealed into a respirometer for post-exercise measurement of oxygen consumption rate (ṀO2), and (ii) the ‘swim tunnel method’, whereby ṀO2 is measured while the fish swims at high speed in a swim tunnel respirometer. In this study, we compared estimates for MMR made using a 3-min exhaustive chase (followed by measurement of ṀO2 in a static respirometer) versus those made via maximal swimming in a swim tunnel respirometer. We made a total of 134 estimates of MMR using the two methods with juveniles of two salmonids (Atlantic salmon Salmo salar and Chinook salmon Oncorhynchus tshawytscha) across a 6°C temperature range. We found that the chase method underestimated ‘true’ MMR (based on the swim tunnel method) by ca. 20% in these species. The gap in MMR estimates between the two methods was not significantly affected by temperature (range of ca. 15–21°C) nor was it affected by body mass (overall range of 53.5–236 g). Our data support some previous studies that have suggested the use of a swim tunnel respirometer generates markedly higher estimates of MMR than does the chase method, at least for species in which a swim tunnel respirometer is viable (e.g. ‘athletic’ ram ventilating fishes). We recommend that the chase method could be used as a ‘proxy’ (i.e. with a correction factor) for MMR in future studies if supported by a species-specific calibration with a relevant range of temperatures, body sizes or other covariates of interest.

Plastic polymers have quickly become one of the most abundant materials on Earth due to their low production cost and high versatility. Unfortunately, some of the discarded plastic can make its way into the environment and become fragmented into smaller microscopic particles, termed secondary microplastics (MP). In addition, primary MP, purposely manufactured microscopic plastic particles, can also make their way into our environment via various routes. Owing to their size and resilience, these MP can then be easily ingested by living organisms. The effect of MP particles on living organisms is suspected to have negative implications, especially during early development. In this study, we examined the effects of polyethylene MP ingestion for four and ten days of exposure starting at 5 days post-fertilization (dpf). In particular, we examined the effects of polyethylene MP exposure on resting metabolic rate, on gene expression of several inflammatory and oxidative stress linked genes, and on microbiome composition between treatments. Overall, we found no evidence of broad metabolic disturbances or inflammatory markers in MP-exposed fish for either period of time. However, there was a significant increase in the oxidative stress mediator L-FABP that occurred at 15 dpf. Furthermore, the microbiome was disrupted by MP exposure, with evidence of an increased abundance of Bacteroidetes in MP fish, a combination frequently found in intestinal pathologies. Thus, it appears that acute polyethylene MP exposure can increase oxidative stress and dysbiosis, which may render the animal more susceptible to diseases.

Fish increase ventilation during hypoxia, a reflex termed the hypoxic ventilatory response (HVR). The HVR is an effective mechanism to increase O2 uptake, but at a high metabolic cost. Therefore, when hypoxia becomes severe enough, ventilation declines, as its benefit is diminished. The water oxygen partial pressure (PwO2) at which this decline occurs is expected to be near the critical PwO2 (Pcrit), the PwO2 at which O2 consumption begins to decline. Our results indicate that in zebrafish (Danio rerio), the relationship between peak HVR and Pcrit was dependent on developmental stage. Peak ventilation occurred at PwO2’s higher than Pcrit in larvae, but at a PwO2 significantly lower than Pcrit in adults. Larval zebrafish use cutaneous respiration to a greater extent than branchial respiration and the cost of sustaining the HVR may outweigh the benefit, whereas adult zebrafish, which rely on branchial respiration, may benefit from using HVR at PwO2 below Pcrit.

Marine organisms living at low temperatures tend to have larger genomes and larger cells which suggest that these traits can be beneficial in colder environments. In fish, triploidy (three complete sets of chromosomes) can be induced experimentally following fertilization, which provides a model system to investigate the hypothesis that larger cells and genomes offers a physiological advantage at low temperatures. We tested this hypothesis by measuring metabolic rates and swimming performance of diploid and triploid Atlantic salmon (Salmo salar) post smolts acclimated to 3 or 10.5 °C. At 10.5 °C, triploids had significantly lower maximum metabolic rates which resulted in a lower aerobic scope compared to diploids. In addition, triploids initiated ram ventilation at lower swimming speeds, providing further evidence of a reduced capacity to meet oxygen demands during strenuous activity at 10.5 °C. However, at 3 °C, metabolic rates and critical swimming speeds were similar between both ploidies, and as expected substantially lower than at 10.5 °C. Therefore, triploidy in colder environments did not provide any advantage over diploidy in terms of metabolic rate traits or swimming performance in Atlantic salmon. We therefore conclude that traits, other than aerobic scope and swimming performance, contribute to the trend for increased cell and genome size in marine ectotherms living in cold environments.

Understanding the determinants and consequences of predation effort, success and prey responses is important since these factors affect the fitness of predators and prey. When predators are also invasive species, the impacts on prey can be particularly far‐reaching with ultimate ecosystem‐level consequences. However, predators are typically viewed as behaviourally fixed within this interaction and it is unclear how variation in predator social dynamics affects predator–prey interactions. Using the invasive eastern mosquitofish Gambusia holbrooki and a native glass shrimp Paratya australiensis in Australia, we investigated how varying levels of social conflict within predator groups influences predator–prey interactions. By experimentally manipulating group stability of G. holbrooki, we show that rates of social conflict were lower in groups with large size differences, but that routine metabolic rates were higher in groups with large size differences. Predation effort and success did not vary depending on group stability, but in stable groups predation effort by aggressive dominants was greater than subordinates. The anti‐predator responses of prey to the stability of predator groups were mixed. While more prey utilized shelters when exposed to stable compared to unstable groups of predators, a greater proportion were sedentary when predator groups were unstable. Overall, this study demonstrates predator group stability is modulated by differences in body size and can influence prey responses. Further, it reveals a hidden metabolic cost of living in stable groups despite reduced overt social conflict. For invasive species management, it is therefore important to consider the behavioural and physiological plasticity of the invasive predators, whose complex social interactions and metabolic demands can modulate patterns of predator–prey interactions.

Many freshwater ecosystems are becoming saltier and/or warmer, but our understanding of how these factors interact and affect the physiology and life history outcomes of most aquatic species remain unknown. We hypothesize that temperature modulates ion transport rates. Since ion transport is energetically expensive, increases in salinity and/or temperature may influence ion flux rates and ultimately, organismal performance. Radiotracer ( 22 Na +, 35 SO −2 4, and 45 Ca 2+ ) experiments with lab-reared mayflies ( N. triangulifer ) and other field-collected insects showed that increasing temperature generally increased ion transport rates. For example, increasing temperature from 15 °C to 25 °C, increased 22 Na + uptake rates by two-fold (p < 0.0001) and 35 SO −2 4 uptake rates by four-fold (p < 0.0001) in the caddisfly, Hydropsyche sparna. Smaller changes in 22 Na + and 35 SO −2 4 uptake rates were observed in the mayflies, Isonychia sayi and Maccaffertium sp., suggesting species-specific differences in the thermal sensitivity of ion transport. Finally, we demonstrated that the toxicity of SO 4 was influenced by temperature profoundly in a 96-h bioassay. Under the saltiest conditions (1500 mg L −1 SO 4 ), mayfly survival was 78 % at 15 °C, but only 44 % at 25 °C (p < 0.0036). Conceivably, the energetic cost of osmoregulation in warmer, saltier environments may cause significant major ion toxicity in certain freshwater insects. Keywords: Temperature, Salinity, Ion transport, Osmoregulation, Toxicity

Climate change is predicted to impact freshwater aquatic environments through changes to water temperature (Twater), river flow and eutrophication. Riverine habitats contain many economically and ecologically important fishes. One such group is the migratory salmonids, which are sensitive to warm Twater and low O2 (hypoxia). While several studies have investigated the independent effects of Twater and hypoxia on fish physiology, the combined effects of these stressors is less well known. Furthermore, no study has investigated the effects of Twater and O2 saturation levels within the range currently experienced by a salmonid species. Thus, the aim of this study was to investigate the simultaneous effects of Twater and O2 saturation level on the energetics and kinematics of steady-state swimming in brown trout, Salmo trutta. No effect of O2 saturation level (70 and 100% air saturation) on tail-beat kinematics was detected. Conversely, Twater (10, 14, 18 and 22°C) did affect tail-beat kinematics, but a trade-off between frequency (ftail) and amplitude (A, maximum tail excursion) maintained the Strouhal number (St = ftail• A/U, where U is swimming speed) within the theoretically most mechanically efficient range. Swimming oxygen consumption rate (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${\dot{M}}_{{\mathsf{O}}_{\mathsf{2}}}$\end{document}) and cost of transport increased with both U and Twater. The only effect of O2 saturation level was observed at the highest Twater (22°C) and fastest swimming speed (two speeds were used—0.6 and 0.8 m s−1). As the extremes of this study are consistent with current summer conditions in parts of UK waterways, our findings may indicate that S. trutta will be negatively impacted by the increased Twater and reduced O2 levels likely presented by anthropogenic climate change.

Organisms with annual life cycles are exposed to life stage specific thermal environments across seasons. Seasonal variation in thermal environments can vary across years and among sites. We investigated how organisms with annual life cycles respond to predictable seasonal changes in temperature and unpredictable thermal variation between habitats and years throughout their lives. Field surveys and historical records reveal that the spatially and temporally heterogeneous thermal environments inhabited by the annual mayfly Ephemerella maculata (Ephemerellidae) shift the date for transition to the next, life stage, so that the thermal phenotype of each life stage matches the thermal environment of the specific habitat and year. Laboratory studies of three distinct life stages of this mayfly reveal that life stage transitions are temperature dependent, facilitating timing shifts that are synchronized with the current season’s temperatures. Each life stage exhibited specific thermal sensitivity and performance phenotypes that matched the ambient temperature typically experienced during that life stage. Our study across the whole life cycle reveals mechanisms that allow organisms to achieve lifetime eurythermy in a dynamic seasonal environment, despite having narrower thermal ranges for growth and development in each life stage.

Reefs are structurally complex habitats that are degraded in numerous coastal areas. Structural complexity is often associated with elevated fish abundance, and recent studies have indicated that such structural complexity (e.g. reefs) not only acts as a fish aggregator, but also increases fish production. The objective of this study was to advance this knowledge by investigating if an underlying mechanism of the observed productivity is related to reduced metabolic rates (proxy for energy use) of fish in reef habitats. Using juvenile Atlantic cod Gadus morhua, we tested the hypothesis that fish energy use differs between fish occupying stone reef and sand bottom habitats. Metabolic rate (MO 2 ) was estimated using intermittent flow respirometry in simulated stone reef and sand bottom habitats over 24 h. Results revealed that G. morhua in the stone reef habitat exhibited significantly reduced accumulated MO 2 compared to G. morhua in the sand bottom habitat. Likewise, there was a tendency for lower mean standard metabolic rates of the fish in stone reefs, although this pattern was not statistically significant. There are many mechanisms that may underpin elevated productivity in structurally complex habitats such as reefs, including better access to shelter and increased food availability. Our study adds to these mechanisms by showing that G. morhua save energy when occupying stone reefs as compared to sandy bottoms, energy which may be allocated to somatic and gonadal growth.

Hypoxia is a pervasive stressor in aquatic environments, and both phenotypic plasticity and evolutionary adaptation could shape the ability to cope with hypoxia. We investigated evolved variation in hypoxia tolerance and the hypoxia acclimation response across fundulid killifishes that naturally experience different patterns of hypoxia exposure. We compared resting O2 consumption rate (ṀO2), and various indices of hypoxia tolerance [critical O2 tension (Pcrit), regulation index (RI), O2 tension (PO2) at loss of equilibrium (PLOE) and time to LOE (tLOE) at 0.6 kPa O2] in Fundulus confluentus, Fundulus diaphanus, Fundulus heteroclitus, Fundulus rathbuni, Lucania goodei and Lucania parva. We examined the effects of chronic (28 days) exposure to constant hypoxia (2 kPa) or nocturnal intermittent hypoxia (12 h normoxia:12 h hypoxia) in a subset of species. Some species exhibited a two-breakpoint model in ṀO2 caused by early, modest declines in ṀO2 in moderate hypoxia. We found that hypoxia tolerance varied appreciably across species: F. confluentus was the most tolerant (lowest PLOE and Pcrit, longest tLOE), whereas F. rathbuni and F. diaphanus were the least tolerant. However, there was not a consistent pattern of interspecific variation for different indices of hypoxia tolerance, with or without taking phylogenetic relatedness into account, probably because these different indices are underlain by partially distinct mechanisms. Hypoxia acclimation generally improved hypoxia tolerance, but the magnitude of plasticity and responsiveness to different hypoxia patterns varied interspecifically. Our results therefore suggest that hypoxia tolerance is a complex trait that is best appreciated by considering multiple indices of tolerance.

Differences between individuals in behavioral type (i.e. animal personality) are ecologically and evolutionarily important because they can have significant effects on fitness components such as growth and predation risk. In the present study we ere used the invasive round goby ( Neogobius melanostomus ) from an established population in controlled experiments to examine the relationships among personality, metabolic performance, and growth rate (inferred as size-at-age). Boldness was measured as the time to return to normal behavior after a simulated predator attack, where fish with shorter freezing times were categorized as “bold” and fish with longer times were categorized as “shy.” We show that bold fish have significantly higher standard metabolic rate (SMR) than their shy conspecifics, whereas there was no difference between personality types in their maximum metabolic rate (MMR) or aerobic scope (AS). Bold fish furthermore had a smaller size-at-age as compared to shy fish. Together this provides evidence of a metabolic underpinning of personality where the high-SMR bold fish require more resources to sustain basic life functions than their low-SMR shy conspecifics, indicating that bold round goby from established populations with high densities (and high competition for food) pay a price of reduced growth rate.

The relationship between individual physiological traits and social behaviour is an important research area because it can examine how mechanisms of behaviour link to functional outcomes. It is hypothesised that correlative and causative links between physiology and individual behaviour may be altered by social interactions. Here, we assess how nutritional stress (20-h starved, 90-h starved) and routine metabolic rate (RMR) determine the movement and foraging behaviour of threespine sticklebacks (Gasterosteus aculeatus), both individually and in a social context. Results showed that there was no statistically significant relationship between RMR and behaviour. The nutritional stress treatment had significant opposite effects on voluntary swim speed, dependent on whether fish were assayed asocially (alone) or socially (in shoals of three). Greater nutritional stress caused voluntary swimming speeds to reduce in an asocial context but increase in a social context, although both relationships were not significant. Additional results exploring social behaviour parameters such as the frequency and duration of shoaling interactions suggests that alterations in fish swim speed between the two nutritional stress treatments may be due to competition effects. This study links state-dependent individual behaviour to social foraging performance and reinforces the theory that social context is an important modulator of the relationships between physiology and behaviour. Recent research has highlighted that the social environment may shape how physiology and behaviour are linked. This area of research, however, requires data from empirical studies that measure and experimentally manipulate physiological traits of individually identifiable animals and tests them under asocial and social conditions. Using threespine sticklebacks foraging for bloodworms, we show that routine metabolic rate did not have a statistically significant effect on fish locomotion or risk-taking. Greater nutritional deprivation caused fish to decrease their swimming speed when they were alone (likely in an effort to reduce energy expenditure); however, when assayed in groups, competitive forces between shoal mates caused them to swim at faster voluntary speeds. Nutritional stress therefore had a significant socially dependent effect on fish locomotion.

This study evaluated the effect of different environmental temperatures in the physiology of Lutjanus guttatus juveniles by analysing their thermoregulatory behaviour, thermal tolerance, oxygen consumption rates and thermal metabolic scope. Jointly, the effect of acclimation and critical temperatures on heat shock protein 70 (Hsp70) and lactate dehydrogenase (Ldh‐a) gene expressions were also analysed using acclimation temperatures of 20, 23, 26, 29 and 32°C. The results showed that the final preferred temperature in juvenile snapper was 26°C with a thermal window of 336.5°C², which was related to an optimal temperature for their physiology determined by the routine metabolic rate and thermal metabolic scope. At temperatures from 20 to 26°C, the routine metabolic rate and Hsp70 and Ldh‐a genes had the lowest values related to a basal expression level. At acclimation temperatures from 29 to 32°C and after critical thermal maximum (CTₘₐₓ) limit, the relative expression of Hsp70 and Ldh‐a genes increased significantly, but the main response at CTₘₐₓ was the upregulation of Hsp70 gene.

Mussels are at particular risk from thermal stress and hypoxia due to limited range and mobility. Of interest to managers is whether sensitivity is uniform or varies among species and subpopulations. We used respirometry to investigate effects of temperature on energy demand and hypoxia tolerance of two narrowly distributed species (Cyclonaias petrina, Colorado River; C. necki, Guadalupe River), and two subpopulations of a widely distributed species (C. pustulosa: Colorado and Navasota rivers) in central Texas. We observed zero mortality during acclimation and respirometry runs even when mussels were exposed to hypoxic conditions for several hours at 36 °C. However, type and magnitude of sublethal effects varied across species and subpopulations as temperatures increased. C. pustulosa (Colorado River) exhibited the greatest increase in energy demand, C. petrina exhibited a decreasing ability to regulate oxygen consumption and an increase in critical dissolved oxygen concentration, C. pustulosa (Navasota River) exhibited metabolic depression, and both C. petrina and C. necki exhibited increasing frequency of valve closure. Results suggest that effects of increasing temperature on energetic requirements are more important than effects on hypoxia tolerance. Management strategies considering physiological differences among species and/or subpopulations are likely to be more effective than a simple “one-size-fits-all” approach.

One measure of hypoxia tolerance is critical oxygen threshold, Pcrit, which is the point where standard metabolism can no longer be maintained through aerobic processes. Traditionally, Pcrit was determined using closed respirometry, whereby the fish's respiration naturally lowered O2. More recently intermittent-flow techniques have been adopted, where N2 is used to displace O2, which ostensibly reduces end-product build-up. This study used a paired design on the marine teleost, red drum. Pcrit is comparable between closed (4.6±0.2 kPa; mean±s.e.m.) and intermittent-flow (4.4±0.2 kPa; mean±s.e.m.) respirometry. pCO2, ammonia, and pH changes within the chamber were measured prior to the onset of Pcrit and at the end of a typical Pcrit trial and revealed changes in water chemistry in both closed and intermittent-flow. Pcrit values were similar in both methods of hypoxia induction regardless of subsequent water chemistry changes that occurred in both methods.

Many vertebrate animals employ anaerobic pathways during high‐speed exercise, even if it imposes an energetic cost during postexercise recovery, expressed as excess postexercise oxygen consumption (EPOC). In ectotherms such a fish, the initial anaerobic contribution to exercise is often substantial. Even so, fish may recover from anaerobic pathways as swimming exercise ensues and aerobic metabolism stabilizes, thus total energetic costs of exercise could depend on swimming duration and subsequent physiological recovery. To test this hypothesis, we examined EPOC in striped surfperch ( Embiotoca lateralis ) that swam at high speeds (3.25 L s −1 ) during randomly ordered 2‐, 5‐, 10‐, and 20‐min exercise periods. We found that EPOC was highest after the 2‐min period (20.9 mg O 2 kg −1 ) and lowest after the 20‐min period (13.6 mg O 2 kg −1 ), indicating that recovery from anaerobic pathways improved with exercise duration. Remarkably, EPOC for the 2‐min period accounted for 72% of the total O 2 consumption, whereas EPOC for the 20‐min period only accounted for 14%. Thus, the data revealed a striking decline in the total cost of transport from 0.772 to 0.226 mg O 2 ·kg −1 ·m −1 during 2‐ and 20‐min periods, respectively. Our study is the first to combine anaerobic and aerobic swimming costs to demonstrate an effect of swimming duration on EPOC in fish. Clarifying the dynamic nature of exercise‐related costs is relevant to extrapolating laboratory findings to animals in the wild. Research Highlight Many animal species employ anaerobic pathways during exercise, though this later imposes an energetic cost, that is, excess postexercise oxygen consumption (EPOC). Our study combined anaerobic and aerobic swimming costs to show an effect of swimming duration on fish exercise recovery and EPOC.

The fatty acid (FA) profile of oysters generally reflects the dietary FA composition. Moreover, incorporation of FA into tissues is modulated by various metabolic factors, and final composition will depend upon the dietary sources, cumulative intake, and oysters' development stage. Thus, the aim of this study was to assess the impact of dietary incorporation of seaweed (SW) Ulva rigida, in replacement of traditional microalgae diet, on the FA composition of Pacific oysters Crassostrea gigas, during broodstock conditioning. The dietary conditioning consisted of direct replacement of microalgae (33% Tisochrysis lutea, 50.25% Skeletonema costatum, and 16.75% Chaetoceros calcitrans ) by SW at four different substitution levels (0%, 25%, 50%, and 100% diet). The dietary docosahexaenoic acid (DHA) (22:6n‐3) and eicosapentaenoic acid (EPA) (20:5n‐3) contents showed a positive correlation with the dietary microalgae level. During the trial, oysters fed with higher percentages of microalgae revealed a depletion of DHA and accumulation of EPA. The 100% SW caused a significant reduction in oxygen consumption and, consequently, in the standard metabolic rate. Based on these results, a partial substitution of up to 25% of dietary microalgae seems to be a suitable alternative, because it elicited similar results to the commercial 100% microalgae diet.

Sympatric speciation occurs without geographical barriers and is thought to often be driven by ecological specialization of individuals that eventually diverge genetically and phenotypically. Distinct morphologies between sympatric populations occupying different niches have been interpreted as such differentiating adaptive phenotypes, yet differences in performance and thus likely adaptiveness between them were rarely tested. Here, we investigated if divergent body shapes of two sympatric crater lake cichlid species from Nicaragua, one being a shore‐associated (benthic) species while the other prefers the open water zones (limnetic), affect cruising (U crit ) and sprinting (U sprint ) swimming abilities – performances particularly relevant to their respective lifestyles. Furthermore, we investigated species differences in oxygen consumption (MO 2 ) across different swimming speeds and compare gene expression in gills and white muscle at rest and during exercise. We found a superior cruising ability in the limnetic Amphilophus zaliosus compared to the benthic Amphilophus astorquii, while sprinting was not different, suggesting that their distinct morphologies affect swimming performance. Increased cruising swimming ability in A. zaliosus was linked to a higher oxygen demand during activity (but not rest), indicating different metabolic rates during exercise ‐ a hypothesis supported by coinciding gene expression patterns of gill transcriptomes. We identified differentially expressed genes linked to swimming physiology, regulation of swimming behaviour and oxygen intake. A combination of physiological and morphological differences may thus underlie adaptations to these species' distinct niches. This complex ecological specialization probably resulted in morphological and physiological trade‐offs that contributed to the rapid establishment and maintenance of divergence with gene flow. see also the Perspective by Gaither et al

Swimming performance is a key feature that mediates fitness and survival in many fish species. Using a swim tunnel respirometer, we compared prolonged swimming performance and energy use for two competing species: an endangered, endemic toothcarp ( Aphanius iberus ) and a worldwide invasive mosquitofish ( Gambusia holbrooki ). Critical ( U crit ) and optimal swimming speeds, standard and maximal metabolic rates, absolute aerobic scope, as well as the minimum cost of transport were estimated and compared between species and sexes. Body streamlining and caudal peduncle depth were also measured to explain the differences in swimming performance and efficiency. Both sexes of A. iberus presented similar swimming capacity and metabolic traits, whereas males of G. holbrooki showed higher critical swimming speeds, maximal metabolic rate and absolute aerobic scope than females. We also found marked differences between species in most of the response variables examined. Aphanius iberus showed lower swimming capacity ( U crit mean <10 cm s −1 ), higher maximal metabolic rate and absolute aerobic scope than the invasive species. By contrast, G holbrooki swam faster and had lower cost of transport at a given fish mass and speed, thereby leading to a higher swimming efficiency. The observed differences in swimming efficiency were closely related to differences in morphological characteristics and therefore to drag pressures and propulsion. Our results add a mechanistic basis to the ecological understanding of these two species and suggest that although both are poor swimmers compared to many other similarly sized species, the native species likely has more restricted water flow tolerance and dispersal capacities.

Background Dietary nitrate improves exercise performance by reducing the oxygen cost of exercise, although the mechanisms responsible are not fully understood. Objectives We tested the hypothesis that nitrate and nitrite treatment would lower the oxygen cost of exercise by improving mitochondrial function and stimulating changes in the availability of metabolic fuels for energy production. Methods We treated 9-mo-old zebrafish with nitrate (sodium nitrate, 606.9 mg/L), nitrite (sodium nitrite, 19.5 mg/L), or control (no treatment) water for 21 d. We measured oxygen consumption during a 2-h, strenuous exercise test; assessed the respiration of skeletal muscle mitochondria; and performed untargeted metabolomics on treated fish, with and without exercise. Results Nitrate and nitrite treatment increased blood nitrate and nitrite levels. Nitrate treatment significantly lowered the oxygen cost of exercise, as compared with pretreatment values. In contrast, nitrite treatment significantly increased oxygen consumption with exercise. Nitrate and nitrite treatments did not change mitochondrial function measured ex vivo, but significantly increased the abundances of ATP, ADP, lactate, glycolytic intermediates (e.g., fructose 1,6-bisphosphate), tricarboxylic acid (TCA) cycle intermediates (e.g., succinate), and ketone bodies (e.g., β-hydroxybutyrate) by 1.8- to 3.8-fold, relative to controls. Exercise significantly depleted glycolytic and TCA intermediates in nitrate- and nitrite-treated fish, as compared with their rested counterparts, while exercise did not change, or increased, these metabolites in control fish. There was a significant net depletion of fatty acids, acyl carnitines, and ketone bodies in exercised, nitrite-treated fish (2- to 4-fold), while exercise increased net fatty acids and acyl carnitines in nitrate-treated fish (1.5- to 12-fold), relative to their treated and rested counterparts. Conclusions Nitrate and nitrite treatment increased the availability of metabolic fuels (ATP, glycolytic and TCA intermediates, lactate, and ketone bodies) in rested zebrafish. Nitrate treatment may improve exercise performance, in part, by stimulating the preferential use of fuels that require less oxygen for energy production. Keywords: ATP, fatty acids, ketone bodies, lactate, mitochondria, metabolomics, nitrate, nitrite, nitric oxide

Many recreational anglers practice catch-and-release; however, research indicates that capture and handling has the potential to adversely affect fish. Numerous catch-and-release studies have been conducted during warmer months, but little work has been done during the winter when ice-anglers in temperate regions target fish. We conducted an ice angling simulation that quantified the impacts of air temperature and air exposure duration on swimming performance and gill physiology of Bluegill Lepomis macrochirus and Largemouth Bass Micropterus salmoides. In all experiments, fish were first subjected to a simulated angling bout in water at 5°C, followed by 30 s or 5 min of air exposure at above freezing (3–8°C) or subfreezing (−7°C) temperatures. The fish were then assessed for critical swimming speed (Bluegill), oxygen consumption (Bluegill), burst swimming (Largemouth Bass), or gill damage (Largemouth Bass). Results showed that Bluegill subjected to 5 min of air exposure at −7°C suffered impaired swimming, with a 47% loss in critical swimming speed (Ucrit) compared with the controls. Treatment had no impact on burst swimming or gill damage in Largemouth Bass. The results demonstrate the possible impacts of air exposure on fish, and we recommend that ice-anglers make an effort to minimize air exposure duration, especially when air temperatures are low.

Taurine (Tau) is an amino sulfonic acid, which is widely distributed in animal tissues, whereas it is almost lacking in plants with the exception of certain algae, seaweeds, and few others. In the aquafeed industry, Tau is mainly used as a feed additive to promote growth in marine fish species with limited cysteine sulfinate decarboxylase activity. In particular, Tau supplementation is required in feeds in which fishmeal (FM) is substituted with high percentages of plant-derived protein sources such as soybean meals (SBM) that have much lower levels of Tau than FM. In addition to being a growth promoter, Tau exert powerful antioxidant properties being a scavenger of the reactive oxygen species (ROS). Under sustained swimming conditions, an intracellular increase in ROS production can occur in fish red muscle where the abundance of mitochondria (the main site of ROS formation) is high. Accordingly, this study aimed at investigating the effects of dietary Tau on European seabass (Dicentrarchus labrax) growth and oxidative stress response induced by swimming exercise. Individually tagged fish of 92.57 ± 20.33 g mean initial weight were fed two experimental diets containing the same low percentage of FM and high percentage of SBM. One diet was supplemented with 1.5% of Tau. Tau supplemented in the diet had a positive effect on fish growth, and enhanced swimming performance and antioxidant status. Two swim endurance tests were performed during the feeding trial. Metabolic oxygen consumption (MO2) was measured during exercise at incremental swimming speeds (0.7, 1.4, 2.1, 2.8, 3.5, and then 4.2 BL (body length) s−1, until fatigue). Fish maximal sustainable swimming speed (Ucrit) was determined too. To investigate the antioxidant effect of dietary Tau, we also measured ROS production in fish blood by RBA (respiratory burst activity) assay and quantified the expression of genes coding for antioxidant enzymes by qPCR (quantitative polymerase chain reaction), such as SOD (superoxide dismutase), GPX (glutathione peroxidase), and CAT (catalase) in red muscle and liver. There was a significant effect of Tau upon Ucrit during exercise. Additionally, ROS production was significantly lower in fish fed with Tau supplemented diet, supporting the role of Tau as ROS scavenger. The protective effect of Tau against oxidative stress induced by forced swimming was denoted also by a significant decrease in antioxidant enzymes gene expression in fish liver and muscle. Taken together these results demonstrate that Tau is beneficial in low FM-based diets for seabass.

In this study, swim-tunnel respirometry was performed on Atlantic salmon Salmo salar post-smolts in a 90 l respirometer on individuals and compared with groups or individuals of similar sizes tested in a 1905 l respirometer, to determine if differences between set-ups and protocols exist. Standard metabolic rate (SMR) derived from the lowest oxygen uptake rate cycles over a 20 h period was statistically similar to SMR derived from back extrapolating to zero swim speed. However, maximum metabolic rate (MMR) estimates varied significantly between swimming at maximum speed, following an exhaustive chase protocol and during confinement stress. Most notably, the mean (± SE) MMR was 511 ± 15 mg O2 kg-1 h-1 in the swim test which was 52% higher compared with 337 ± 9 mg O2 kg-1 in the chase protocol, showing that the latter approach causes a substantial underestimation. Performing group respirometry in the larger swim tunnel provided statistically similar estimates of SMR and MMR as for individual fish tested in the smaller tunnel. While we hypothesised a larger swim section and swimming in groups would improve swimming performance, Ucrit was statistically similar between both set-ups and statistically similar between swimming alone v. swimming in groups in the larger set-up, suggesting that this species does not benefit hydrodynamically from swimming in a school in these conditions. Different methods and set-ups have their own respective limitations and advantages depending on the questions being addressed, the time available, the number of replicates required and if supplementary samplings such as blood or gill tissues are needed. Hence, method choice should be carefully considered when planning experiments and when comparing previous studies. This article is protected by copyright. All rights reserved.

Many fish naturally encounter a daily cycle of hypoxia but it is unclear whether this exposure hardens hypoxia-intolerant fish to future hypoxia or leads to accumulated stress and death. Rainbow trout (Oncorhynchus mykiss) is a putatively hypoxia-sensitive species found in rivers and estuaries that may routinely experience hypoxic events. Trout were exposed to 1 of 4 135h treatments in a swim-tunnel respirometer: 1) air-saturated control (20.7 kPa PO2); 2) diel cycling O2 (20.7-4.2 kPa over 24h); 3) acute hypoxia (130h at 20.7 kPa PO2 followed by 5h at 4.2 kPa PO2); 4) the mean oxygen tension (12.4 kPa PO2) experienced by the diel cycled fish. Some responses were similar in diel O2 cycled and mean PO2-treated fish but overall exposure to ecologically-representative diel hypoxia cycles improved hypoxia tolerance. Diel hypoxia-induced protective responses included increased inducible HSP70 concentration and mean corpuscular hemoglobin concentration, as well as reduced plasma cortisol. Acclimation to diel hypoxia allowed metabolic rates to decline during hypoxia, reduced oxygen debt following subsequent exposures, and allowed fish to return to an anabolic phenotype. The data demonstrate that acute diel cycling hypoxia improves hypoxia tolerance in previously intolerant fish through the activation of cellular protective mechanisms and a reduction in metabolic O2 requirements.

The energy used to move a given distance (cost of transport; CoT) varies significantly between individuals of the same species. A lower CoT allows animals to allocate more of their energy budget to growth and reproduction. A higher CoT may cause animals to adjust their movement across different environmental gradients to reduce energy allocated to movement. The aim of this project was to determine whether CoT is a repeatable trait within individuals, and to determine its physiological causes and ecological consequences. We found that the CoT is a repeatable trait in zebrafish (Danio rerio). We rejected the hypothesis that mitochondrial efficiency (P/O ratios) predicted CoT. We also rejected the hypothesis that CoT is modulated by temperature acclimation, exercise training, or their interaction, although CoT increased with increasing acute test temperature. There was a weak but significant negative correlation between CoT and dispersal, measured as the number of exploration decisions made by fish, and the distance travelled against the current in an artificial stream. However, CoT did not correlate with the voluntary speed of fish moving against the current. The implications of these results are that CoT reflects a fixed physiological phenotype of an individual, which is not plastic in response to persistent environmental changes. Consequently, individuals may have fundamentally different energy budgets as they move across environments, and may adjust movement patterns as a result of allocation trade-offs. It was surprising that mitochondrial efficiency did not explain differences in CoT, and our working hypothesis is that the energetics of muscle contraction and relaxation may determine CoT. The increased in CoT with increasing acute environmental temperature means that warming environments will increase the proportion of the energy budget allocated to locomotion unless individuals adjust their movement patterns.

Highly unsaturated fatty acids of the omega-3 series (HUFA) are major constituents of cell membranes, yet poorly synthesised de novo by consumers. Their production, mainly supported by aquatic microalgae, has been decreasing with global change. Understanding the consequences of such reductions is essential for ectotherm consumers, since temperature tightly regulates the HUFA content in cell membranes, maintaining their functionality. Integrating individual, tissue and molecular approaches, we examined the consequences of the combined effects of temperature and HUFA depletion on the key cardio-respiratory functions of the golden grey mullet, an ectotherm grazer of high ecological importance. For four months, fish were exposed to two contrasting HUFA diets (4.8% ecosapentaenoic acid (EPA)+docosahexaenoic acid (DHA) on dry matter (DM) vs. 0.2% EPA+DHA on DM) at 12°C and 20°C. Ventricular force development coupled with gene expression profiles measured on cardiac muscle suggest that combining HUFA depletion with warmer temperatures leads to (1) a proliferation of sarcolemmal and SR Ca2+ channels and (2) a higher force-generating ability by increasing extracellular Ca2+ influx via sarcolemmal channels when the heart has to sustain excessive effort due to stress and/or exercise. At the individual scale, these responses were associated with a relatively greater aerobic scope, maximum metabolic rate and net cost of locomotion, suggesting the higher energy cost of this strategy. These impaired cardiac performances could have wider consequences on other physiological performances such as growth, reproduction or migration, all greatly depending on heart function.

Water temperature is known to be a particularly important environmental factor that affects fish swimming performance, but it is unknow how acute temperature changes affect the fish performance of Ptychobarbus kaznakovi. P. kaznakovi in the Lancang River have declined quickly in recent years, and this species was used to examine the effects of acute temperature changes on swimming abilities and oxygen consumption in a Brett‐type swimming tunnel respirometer. The standard metabolic rate (SMR) and routine metabolic rate (RMR) showed 216% and 134% increases, respectively, at 22°C (an acute increase from 17 to 22°C) compared to those at 12°C (an acute decrease from 17 to 12°C). Moreover, the RMR was approximately 1.7, 1.6 and 1.3 times the value of the SMR at 12°C, 17°C and 22°C, respectively. The critical swimming speed (Ucᵣᵢₜ) of P. kaznakovi at 22°C was 5.45 ± 0.45BL/S, which was 45% higher than that at 12°C (3.77 ± 0.92BL/S). The oxygen consumption rates (MO₂) reached their maximum values at swimming speeds near the Ucᵣᵢₜ for all the temperature treatments. The maximum metabolic rate (MMR) values at 12°C, 17°C and 22°C were 274.53 ± 142.60 (mgO₂ kg⁻¹ hr⁻¹), 412.85 ± 216.34 (mgO₂ kg⁻¹ hr⁻¹) and 1,095.73 ± 52.50 (mgO₂ kg⁻¹ hr⁻¹), respectively. Moreover, there was a narrow aerobic scope at 12°C compared to that at 17°C and 22°C. The effect of acute temperature changes on the swimming abilities and oxygen consumption of P. kaznakovi indicated that water temperature changes caused by dam construction could directly affect energy consumption during the upstream migration of fish.

Field metabolic rate (FMR) is key to understanding individual and population-level responses to environmental changes, but is challenging to measure in field conditions, particularly in aquatic environments. Here we show that FMR can be estimated directly from the isotopic composition of carbon in fish otoliths (δ13Coto). We describe the relationship between δ13Coto values and oxygen consumption rate, and report results from laboratory experiments relating individual-level measurements of oxygen consumption rates to δ13Coto values in Atlantic cod (Gadus morhua). We apply our new δ13Coto metabolic proxy to existing δ13Coto data from wild cod and four deepwater fish species to test the validity of inferred FMR estimates. The δ13Coto metabolic proxy offers a new approach to study physiological ecology in free-ranging wild fishes. Otolith-based proxies for FMR are particularly promising as they allow retrospective assessment of time-integrated, individual-level FMR throughout an individual fish’s life history. Ming-Tsung Chung et al. report a method for estimating field metabolic rate (FMR) in teleost fishes using the isotopic composition of carbon found in inner ear structures called otoliths. They show that their method can provide accurate estimates of FMR for free-ranging wild fishes and allows for tracking FMR of individual fish over time.

The physiological reasons why salmonids show glucose intolerance are unclear. In mammals, rapid clearance of a glucose load is mainly achieved through insulin-mediated inhibition of hepatic glucose production ( R a ) and stimulation of glucose disposal ( R d ), but the effects of insulin on R a and R d glucose have never been measured in fish. The goal of this study was to characterize the impact of insulin on the glucose kinetics of rainbow trout in vivo. Glucose fluxes were measured by continuous infusion of [6- 3 H]glucose before and during 4 h of insulin administration. The phosphorylated form of the key signaling proteins Akt and S6 in the insulin cascade were also examined, confirming activation of this pathway in muscle but not liver. Results show that insulin inhibits trout R d glucose from 8.6 ± 0.6 to 5.4 ± 0.5 µmol kg −1 min −1: the opposite effect than classically seen in mammals. Such a different response may be explained by the contrasting effects of insulin on gluco/hexokinases of trout versus mammals. Insulin also reduced trout R a from 8.5 ± 0.7 to 4.8 ± 0.6 µmol·kg −1 ·min −1, whereas it can almost completely suppresses R a in mammals. The partial inhibition of R a glucose may be because insulin only affects gluconeogenesis but not glycogen breakdown in trout. The small mismatch between the responses to insulin for R d (−37%) and R a glucose (−43%) gives trout a very limited capacity to decrease glycemia. We conclude that the glucose intolerance of rainbow trout can be explained by the inhibiting effect of insulin on glucose disposal.

Metabolic rate and life history traits vary widely both among and within species reflecting trade-offs in energy allocation, but the proximate and ultimate causes of variation are not well understood. We tested the hypothesis that these trade-offs are mediated by environmental heterogeneity, using isogenic strains of the amphibious fish Kryptolebias marmoratus that vary in the amount of time each can survive out of water. Consistent with pace of life theory, the strain that survived air exposure the longest generally exhibited a “slow” phenotype including the lowest metabolic rate, largest scope for metabolic depression, slowest consumption of energy stores, and least investment in reproduction under standard conditions. Growth rates were fastest in the otherwise “slow” strain, however. We then tested for fitness trade-offs between “fast” and “slow” strains using microcosms where fish were held with either constant water availability or under fluctuating conditions where water was absent for half of the experiment. Under both conditions the “slow” strain grew larger and was in better condition, and under fluctuating conditions the “slow” strain produced more embryos. However, the “fast” strain had larger adult population sizes under both conditions, indicating that fecundity is not the sole determinant of population size in this species. We conclude that genetically based differences in pace of life of amphibious fish determine survival duration out of water. Relatively “slow” fish tended to perform better under conditions of limited water availability, but there was no detectable cost under control conditions. Thus, pace of life differences may reflect a conditionally neutral instead of antagonistic trade-off.

Species with fast life‐histories typically prioritize current over future reproductive events, compared to species with slow life‐histories. These species therefore require greater energetic input into reproduction, and also likely have less time to realize their reproductive potential. Hence, behaviors that increase access to both resources and mating opportunities, at a cost of increased mortality risk, could coevolve with the pace of life‐history. However, whether this prediction holds across species, remains untested under standardized conditions. Here, we test how risky behaviors, which facilitate access to resources and mating opportunities (i.e., activity, boldness, and aggression), along with metabolic rate, coevolve with the pace of life‐history across 20 species of killifish that present remarkable divergences in the pace of life‐history. We found a positive association between the pace of life‐history and aggression, but interestingly not with other behavioral traits or metabolic rate. Aggression is linked to interference competition, and in killifishes is often employed to secure mates, while activity and boldness are more relevant for exploiting energetic resources. Our results suggest that the trade‐off between current and future reproduction plays a more prominent role in shaping mating behavior, while behaviors related to energy acquisition may be influenced by ecological factors.

Despite continuing interest in the proximate energetic constraints on individual variation in behavior, there is presently equivocal evidence for correlations between metabolism and behavior at the among‐individual level. Possible reasons for this include imprecise estimates of individual mean behavior and metabolism due to no repeated measures on one or more of the traits, analyses that do not take into account the labile nature of these traits and the uncertainty in individual estimates, and changing environmental conditions not accounted for. In this empirical study, we repeatedly measured activity rates and resting metabolic rates (RMR) of individual male mosquitofish over an extended period, lasting several months under constant laboratory conditions. Repeatability of each trait was significant (RMR: R =.41; activity: R =.72), indicating consistent variation among individuals, making covariance between them possible. Contrary to expectations, bivariate mixed model analysis revealed that more active individuals had lower RMR ( r = −.58) after accounting for mass effects and other covariates. This result suggests that high activity rates require individuals to allocate less energy toward maintenance, and thus provides evidence for the “allocation” model of energy management. We suggest that it would be valuable to study whether and how behavior‐RMR correlations change over individual lifetime, a topic that has yet to be addressed.

Predicting the potential effects of changes in climate on freshwater species requires an understanding of the relationships between physiological traits and environmental conditions among populations. While water temperature is a primary factor regulating metabolic rates in freshwater ectotherms, how metabolic rates vary across the species range is unclear. In addition, photoperiod has also been hypothesised to influence metabolic rates in freshwater taxa based on seasonal changes in activity rates. Using an experimental approach, we investigated whether variation in routine metabolic rate (RMR) and sensitivity of RMR to changes in temperature are correlated with local thermal regimes, photoperiods and body mass among ten populations across the geographic range of the Bluntnose minnow ( Pimephales notatus ), a North American freshwater fish species. Routine metabolic rate data were collected from populations acclimatised to three temperature treatments (9, 18 and 27°C) and correlated with water temperature and photoperiod estimates at collection locations for each population. Routine metabolic rate was negatively correlated with minimum photoperiod at 9°C, negatively correlated with weekly high temperature at 18°C and positively correlated with weekly high temperature at 27°C. Body mass was also a predictor of RMR at each temperature treatment. Thermal sensitivity of RMR was positively correlated with weekly high temperature, indicating that individuals from warmer low latitude populations experienced greater sensitivity of RMR to changes in temperature than individuals from cooler high latitude populations. These results indicate differential responses among populations to variation in temperature and suggest the importance of recognising this variation when characterising responses of freshwater taxa to increases in water temperature.

The ability to tolerate environmental change may decline as fishes age. We tested the hypothesis that ageing influences the scope for phenotypic flexibility in the mangrove rivulus (Kryptolebias marmoratus), an amphibious fish that transitions between two vastly different environments, water and land. We found that older fish (4–6 years old) exhibited marked signs of ageing; older fish were reproductively senescent, had reduced fin regenerative capacity and body condition, and exhibited atrophy of both oxidative and glycolytic muscle fibers relative to younger adult fish (1–2 years old). However, age did not affect routine O2 consumption. We then acclimated adult fish (1–6 years) to water (control) or air for 10 days to assess the scope for phenotypic flexibility in response to terrestrial exposure. In support of our hypothesis, we found that older air-acclimated fish had a diminished scope for gill remodeling relative to younger fish. We also found that older fish exhibited poorer terrestrial locomotor performance relative to younger adult fish, particularly when acclimated to air. Our results indicate that ageing diminishes skeletal muscle integrity and locomotor performance of amphibious fishes, and may, therefore, impair terrestrial foraging ability, predator avoidance, or dispersal across the terrestrial environment. Remarkably, older fish voluntarily left water to a similar degree as younger fish despite the age-related deterioration of traits important for terrestrial life.

Parasitic infections elicit host defences that pose energetic trade-offs with other fitness-related traits. Bitterling fishes and unionid mussels are involved in a two-way parasitic interaction. Bitterling exploit mussels by ovipositing into their gills. In turn, mussel larvae (glochidia) develop on the epidermis and gills of fish. Hosts have evolved behavioural responses to reduce parasite load, suggesting that glochidia and bitterling parasitism are costly. We examined the energetic cost of parasitism on both sides of this relationship. We used intermittent flow-through respirometry to measure (1) standard metabolic rate (SMR) of individual duck mussels Anodonta anatina (a common bitterling host) before and during infection by embryos of the European bitterling Rhodeus amarus, and (2) SMR and maximum oxygen uptake (MO2max) of individual R. amarus before and during infection with glochidia of the Chinese pond mussel Sinanodonta woodiana (a mussel species that successfully infects bitterling). As predicted, we observed an increase in mussel SMR when infected by bitterling embryos and an increased SMR in glochidia-infected bitterling, though this was significantly mediated by the time post-infection. Contrary to our predictions, glochidia infection did not impair MO2max and the number of glochidia attached to gills positively (rather than negatively) correlated with MO2max. The results suggest that tolerance is the prevailing coping mechanism for both fish and mussels when infected, while resistance mechanisms appear to be confined to the behavioural level.

Seagrasses are identified as a sentinel species: a good indicator of overall marine ecosystem health and function. At the rhizome, they are known to interact with marine bacteria by exchanging energy in the form of glucose and free amino acids secreted through root exudate in exchange for microbe-fixated nitrogen that can be utilized for plant growth. To analyze potential outcomes of possible future changes in light availability, an experiment was designed to collect and analyze the root exudate of Cymodocea nodosa under three light conditions (standard fluorescent light, blue LED, and green LED light). After 72 hours of treatment, the root exudate was examined for glucose, nitrite, nitrate, and ammonia concentrations via spectrophotometry, while respiration was measured utilizing oxygen respirometry. No differences were observed for glucose, free amino acid content, nitrite, or ammonia. The standard fluorescent lightning yielded a significant increase in respiration of C.nodosa. Nitrate displayed a significant increase in both blue and green LED lightning. Due to the shortened experimental time frame it is concluded that a more significant effect could be observed if exudate is studied longitudinally.

Ocean acidification is a growing problem that may affect many marine organisms in the future. Within 100 years the pH of the ocean is predicted to decrease to 7.8, from the current ocean pH of around 8.1. Using phenolic acid levels as a stress indicator as well as respiration and chlorophyll content as a measure of health, the effect of lowering pH was tested on the seagrass, Cymodocea nodosa, in a controlled environment. Plant samples, water, and soil were taken from the Bay of Cádiz, Spain, and placed in aquaria in a temperature-controlled room. One control group was left untreated with a pH of approximately 8.1, while experimental groups maintained pH levels of 7.8 and 7.5. Using High Performance Liquid Chromatography (HPLC), concentration of the phenol rosmarinic acid was quantified in the plants. Average concentration for the control group was 1.7 μg g-1, while it was 2.9 μg g-1 for pH group 7.8, and 10.1g g-1 for pH group 7.5. To evaluate the overall health of C. nodosa within the three groups, chlorophyll concentration and photosynthesis/respiration rates were determined. A one-tailed ANOVA test was conducted using the chlorophyll concentrations of the three groups. With an F-value of 1.360 and a p-value of 0.287, the differences between the groups were not statistically significant. Although the raw data shows a slight decrease in chlorophyll content between the control group and the pH group 7.5, these discrepancies might have been larger or smaller due to sampling or experimental error. Additionally, the average values with their respective standard deviations were calculated for the respiration rates and oxygen production of each group. A one-tailed ANOVA was also used to determine the relationship between rosmarinic acid content and pH levels between the groups, with an F-value of 5.1423 and a p-value of 0.050.

To mitigate salmon lice infestations in Atlantic salmon (Salmo salar) sea cages, deployment of cleaner fish have become a widespread strategy. However, species of cleaner fish may experience poor welfare in the highly fluctuating farm environment owing to differences in physiological adaptations and niche requirements. In particular, occurrences of reduced oxygen levels are common in salmon cages. The purpose of this study was therefore to compare hypoxia responses of Atlantic salmon and two commonly used cleaner fish species, the lumpfish (Cyclopterus lumpus) and the ballan wrasse (Labrus bergylta). We used respirometry to measure metabolic rates (MO2) during progressive hypoxia down to 20% oxygen saturation. In addition, we also measured key haematological parameters before, during and after hypoxia exposure. While all fish survived exposure down to 20% oxygen saturation, distinct differences in metabolic and haematological responses were found, reflecting species specific adaptations and lifestyles. In Atlantic salmon, MO2 was independent of ambient oxygen levels until 27% saturation, after which it decreased linearly. In lumpfish, MO2 steadily decreased throughout the hypoxia trial. In ballan wrasse, MO2 was notably lower than in the other species and unaffected by the levels of hypoxia encountered. Hypoxia induced changes in plasma cortisol, plasma lactate and plasma osmolality were substantially greater in Atlantic salmon compared to both cleaner fish species. This suggests that similar magnitudes of hypoxia exposure were more stressful to Atlantic salmon. Hence, neither cleaner fish species should be in immediate danger as long as hypoxia levels that are known to be detrimental to Atlantic salmon are avoided. However, lumpfish had markedly reduced activity levels at the early onset of progressive hypoxia, and is therefore likely to require near normoxic conditions to efficiently function as cleaner fish.

Over the last decade, ocean temperature on the U.S. Northeast Continental Shelf (U.S. NES) has warmed faster than the global average and is associated with observed distribution changes of the northern stock of black sea bass (Centropristis striata). Mechanistic models based on physiological responses to environmental conditions can improve future habitat suitability projections. We measured maximum, standard metabolic rate, and hypoxia tolerance (Scrit) of the northern adult black sea bass stock to assess performance across the known temperature range of the species. Two methods, chase and swim-flume, were employed to obtain maximum metabolic rate to examine whether the methods varied, and if so, the impact on absolute aerobic scope. A subset of individuals was held at 30°C for one month (30chronic°C) prior to experiments to test acclimation potential. Absolute aerobic scope (maximum–standard metabolic rate) reached a maximum of 367.21 mgO2 kg-1 hr-1 at 24.4°C while Scrit continued to increase in proportion to standard metabolic rate up to 30°C. The 30chronic°C group exhibited a significantly lower maximum metabolic rate and absolute aerobic scope in relation to the short-term acclimated group, but standard metabolic rate or Scrit were not affected. This suggests a decline in performance of oxygen demand processes (e.g. muscle contraction) beyond 24°C despite maintenance of oxygen supply. The Metabolic Index, calculated from Scrit as an estimate of potential aerobic scope, closely matched the measured factorial aerobic scope (maximum / standard metabolic rate) and declined with increasing temperature to a minimum below 3. This may represent a critical threshold value for the species. With temperatures on the U.S. NES projected to increase above 24°C in the next 80-years in the southern portion of the northern stock’s range, it is likely black sea bass range will continue to shift poleward as the ocean continues to warm.

To date, many studies trying to understand species’ climate-driven changes in distribution, or ‘range shifts’, have each focused on a single potential mechanism. While a single performance measure may give some insight, it may not be enough to accurately predict outcomes. Here, we used multiple measures of performance to explore potential mechanisms behind species range shifts. We examined the thermal pattern for multiple measures of performance, including measures of aerobic metabolism and multiple aspects of escape speed, using the final larval stage (puerulus) of eastern rock lobster Sagmariasus verreauxi as a model species. We found that aerobic scope and escape speed had different thermal performances and optimal temperatures. The optimal temperature for aerobic scope was 27.5°C, while the pseudo-optimal temperature for maximum escape speed was 23.2°C. This discrepancy in thermal performance indicators illustrates that one measure of performance may not be sufficient to accurately predict whole-animal performance under future warming. Using multiple measures of performance and appropriate modelling techniques may lead to a more accurate prediction of future range shifts, including the timing and extent of climate-driven species redistribution.

The effects of passive integrated transponder (PIT) tagging on cortisol release, standard metabolic rate (SMR) and daily specific growth rate ( G S ) were evaluated in the Gulf killifish, Fundulus grandis, a small estuarine fish native to the Gulf of Mexico. Cortisol release by individual fish was measured non‐invasively prior to PIT tagging, immediately after tagging and once per week for 1 month following tagging. Within the first 2 h of tagging, cortisol release rates were significantly elevated compared with values measured prior to tagging and significantly higher than that of fish handled identically except not implanted with PIT tags. By 1 week after PIT tagging, cortisol release rates returned to control levels. SMR, determined by intermittent‐flow respirometry and G S, defined as per cent change in body mass per day, were measured prior to PIT tagging and weekly for 1 month after tagging. Neither SMR nor G S was significantly different in tagged v. untagged fish for the duration of the study. One month after tagging, haematocrit, plasma cortisol, blood glucose and blood lactate did not differ between tagged and untagged individuals. Therefore, after a transient stress response that subsides within 1 week, PIT tagging had no significant effects on these physiological variables in F. grandis, validating its use as a method of marking this and other small fishes.

The clownfish Amphiprion ocellaris is widely distributed in the coral reef ecosystems of tropical and subtropical regions of the West Indo Pacific, an area that hosts economically valuable species, and, thus, a suitable candidate for warm water aquaculture. This study determined the preferred temperature, critical threshold limits, represented by critical thermal maximum and critical thermal minimum, thermal window width, and aerobic metabolic scope of A. ocellaris clownfish acclimated to 20, 23, 26, 29, 32, and 35 °C. A positive response (P < 0.05) occurred when the preferred temperature significantly increased with increasing acclimation temperature. The preferred temperature obtained graphically was 30.0 °C. Acclimation temperature significantly affected the thermal tolerance which increased with acclimation temperature. The thermal window calculated for A. ocellaris was 301.5 °C2. The thermal metabolic scope obtained in animals acclimated at the interval from 23 to 32 °C (P > 0.05) had a mean value of 4240.8 mg O2 h−1 kg−1 w.w., revealing that A. ocellaris is a eurythermal species with a range of optimal physiological performance that closely matches the environmental conditions where it can be farmed. Therefore, the highest value of the thermal aerobic scopes corresponded to the intervals of the preferred temperature obtained for A. ocellaris. These results may partially explain their worldwide distribution pattern, as well as their aquaculture potential in tropical regions.

The present study aimed to evaluate the biological responses of Colossoma macropomum to naphthalene injection and subsequent hypoxia exposure, emphasizing the expression of the tumor suppressor gene tp53. Tambaquis were intraperitoneally injected with naphthalene (50 mg/kg) and, after 96 hours, the fish were transferred to respirometry chambers and, submitted to progressive hypoxia for the determination of critical PO2. In a subsequent experiment, the fish received an intraperitoneal injection of naphthalene and were kept for 96 hours under normoxia. Successively, fish were challenged with acute hypoxia (PO2

The increasing human presence in the Arctic shelf seas, with the expansion of oil and gas industries and maritime shipping, poses a risk for Arctic marine organisms such as the key species polar cod (Boreogadus saida). The impact of dietary crude oil on growth and metabolism of polar cod was investigated in the early spring (March-April) when individuals are expected to be in a vulnerable physiological state with poor energy stores. Adult polar cod were exposed dietarily to three doses of Kobbe crude oil during an eight weeks period and followed by two weeks of depuration. Significant dose-responses in exposure biomarkers (hepatic ethoxyresorufine-O-deethylase [EROD] activity and 1-OH phenanthrene metabolites in bile) indicated that polycyclic aromatic hydrocarbons (PAHs) were bioavailable. Condition indices (i.e. Fulton's condition factor, hepatosomatic index), growth, whole body respiration, and total lipid content in the liver were monitored over the course of the experiment. The majority of females were immature, while a few had spawned during the season and showed low hepatic lipid content during the experiment. In contrast, males were all, except for one immature individual, in a post-spawning stage and had larger hepatic energy stores than females. Most specimens, independent of sex, showed a loss in weight, that was exacerbated by exposure to crude oil and low hepatic liver lipids. Furthermore, females exposed to crude oil showed a significant elevation of oxygen consumption compared to controls, although not dose-dependent. This study highlights the importance of the energy status of individuals for their response to a crude oil exposure.

Phenotypic polymorphisms often differ in multiple correlated traits including morphology, behavior, and physiology, all of which can affect performance. How selection acts on these suites of traits can be complex and difficult to discern. Starry flounder ( Platichthys stellatus ) is a pleuronectid flatfish that exhibits rare polymorphism for the direction of eye migration and resulting whole‐body asymmetry. P. stellatus asymmetry morphs differ subtly in several anatomical traits, foraging behavior, and stable isotope signatures, suggesting they may be ecologically segregated, yet performance and metabolic differences are unknown. Here we tested the hypothesis that sinistral and dextral P. stellatus asymmetry morphs diverge in performance and routine metabolic rate (RMR) by comparing prolonged swimming endurance (time to exhaustion at a constant swimming speed), fast‐start swimming velocity and acceleration, and rate of oxygen consumption. Based on subtle morphological differences in caudal tail size, we expected sinistral P. stellatus to have superior prolonged swimming endurance relative to dextral fish, but inferior fast‐start performance. Sinistral P. stellatus exhibited both significantly greater prolonged swimming performance and fast‐start swimming performance. However, sinistral P. stellatus also exhibited greater RMR, suggesting that their general swimming performance could be enhanced by an elevated metabolic rate. Divergence between P. stellatus asymmetry morphs in swimming performance and metabolic rates contributes to growing evidence of ecological segregation between them, as well as our understanding of possible ecological consequences of asymmetry direction in flatfishes. These data provide an example of the complexity of polymorphisms associated with multiple correlated traits in a rare case of asymmetry polymorphism in a marine flatfish species.

Purely diffusive O 2 transport typically is insufficient to sustain aerobic metabolism in most multicellular organisms. In animals that are small enough, however, a high surface-to-volume ratio may allow passive diffusion alone to supply sufficient O 2 transfer. The purpose of this study was to explore the impacts of internal convection on respiratory gas transfer in a small complex organism, the larval zebrafish ( Danio rerio). Specifically, we tested the hypothesis that internal convection is required for the normal transfer of the respiratory gases O 2 and CO 2 and maintenance of resting aerobic metabolic rate in larvae at 4 days postfertilization (dpf). Morpholino knockdown of the vascular endothelial growth factor (VEGF) or cardiac troponin T (TNNT2) proteins allowed an examination of gas transfer in two independent models lacking internal convection. With the use of a scanning micro-optrode technique to measure regional epithelial O 2 fluxes ( Jo 2 ), it was demonstrated that larvae lacking convection exhibited reduced Jo 2 in regions spanning the head to the trunk. Moreover, the acute loss of internal convection caused by heart stoppage resulted in reduced rates of cutaneous Jo 2, an effect that was reversed upon the restoration of internal convection. With the use of whole body respirometry, it was shown that loss of internal convection was associated with reduced resting rates of O 2 consumption and CO 2 excretion in larvae at 4 dpf. The results of these experiments clearly demonstrate that internal convection is required to maintain resting rates of respiratory gas transfer in larval zebrafish.

The ability to measure oxygen consumption rates of a living organism in real-time provides an indirect method of monitoring dynamic changes in metabolism reflecting organismal level mitochondrial function. In this study, we assessed the Loligo Systems microplate system for measuring individual respiration in small organisms. This included adult nematodes (Caenorhabditis elegans, N2), zebrafish embryos (Danio rerio, AB), and adult fruit flies (Drosophila melanogaster, w1118). Organisms were placed inside 80 µL glass chambers on a 24-well microplate atop a 24-channel optical fluorescence oxygen reading device. Adult nematodes and zebrafish embryos were in liquid culture, M9 buffer and egg water respectively, and the adult flies were in room air. The microplate and reader were placed inside an incubator for temperature control. A silicone gasket with a thin liner was used to seal the chambers. Reference standard oxygen consumption (respiration) of single and multiple adult nematodes (n=1–4 animals/well), zebrafish embryos (n=1–4 animals/well), and adult flies (n=1–2 animals/well) in the microplate system were achieved. Significant differences across numbers of animals/well and by sex were observed. Validation experiments of the oxygen consumption rates measured in C. elegans in parallel with Seahorse extracellular flux (XF) experiments are underway. The Loligo Systems microplate system offers a non-invasive, non-destructive method to measure real-time respiration in smaller organisms. These data provide preliminary evidence for utility of the system for a variety of biomedical applications that relate to organismal and mitochondrial function/dysfunction, including research in the basic biology of aging in these highly-utilized, pre-clinical, genetic model organisms.

Aquatic ectotherms face a challenge of obtaining sufficient oxygen, and it is commonly claimed that this challenge increases with increasing environmental temperature, causing concerns about the fate of aquatic ecosystems under climate change. However, the oxygen challenge hypothesis often ignores the effect of known phenotypic plastic responses. These can occur on either a within‐ or multigenerational scale, where multiple reactions act in concert to increase oxygen supply in response to increased temperature in a wide range of traits (molecular, egg content, behavioural, cell structure, morphological). Here, we combine a novel modelling approach with empirical measurements that enable quantification of how both the oxygen supply (maximum oxygen diffusion rate) and demand (metabolic rate) are affected by temperature while allowing for phenotypic plasticity. We exposed the aquatic ectotherm Daphnia magna to a range of temperatures (17–28°C) over several asexual generations and confirm that phenotypic plasticity contributes to an increased ability to obtain oxygen on the whole‐organism level at high temperatures. This response is strongest within the highest temperature range (22–28°C), where the change in oxygen challenge is expected to be most pronounced. However, the observed thermal plasticity in oxygen supply failed to compensate for the increased demand. Thus, we provide empirical evidence that the oxygen challenge in aquatic ectotherms increases with increasing temperature, even in the presence of phenotypic plasticity in oxygen supply.

3-ketodihydrosphingosine reductase (KDSR) is the key enzyme in the de novo sphingolipid synthesis. We identified a novel missense kdsrI105R mutation in zebrafish that led to a loss of function, and resulted in progression of hepatomegaly to steatosis, then hepatic injury phenotype. Lipidomics analysis of the kdsrI105R mutant revealed compensatory activation of the sphingolipid salvage pathway, resulting in significant accumulation of sphingolipids including ceramides, sphingosine and sphingosine 1-phosphate (S1P). Ultrastructural analysis revealed swollen mitochondria with cristae damage in the kdsrI105R mutant hepatocytes, which can be a cause of hepatic injury in the mutant. We found elevated sphingosine kinase 2 (sphk2) expression in the kdsrI105R mutant. Genetic interaction analysis with the kdsrI105R and the sphk2wc1 mutants showed that sphk2 depletion suppressed liver defects observed in the kdsrI105R mutant, suggesting that liver defects were mediated by S1P accumulation. Further, both oxidative stress and ER stress were completely suppressed by deletion of sphk2 in kdsrI105R mutants, linking these two processes mechanistically to hepatic injury in the kdsrI105R mutants. Importantly, we found that the heterozygous mutation in kdsr induced predisposed liver injury in adult zebrafish. These data point to kdsr as a novel genetic risk factor for hepatic injury.

Much is known about the genetic variance in certain components of metabolism, most notably resting and maximum metabolic rate. This is in stark contrast to the lack of information on genetic variance in the metabolic rate of individuals that feed and express routine activity, and how this rate correlates with other components of the energy budget or life history traits. Here we quantify genetic variance in metabolic rate (MR) under such conditions, as well as food consumption, juvenile somatic growth rate and age at maturation under ad lib food availability in a set of 10 clones of Daphnia magna from a natural population. Broad sense evolvabilities (0.16–0.56%) were on the same order of magnitude as those typically observed for physiological and life history traits, and suggest that all these traits have the potential to evolve within this population. We did not find support for the previously hypothesized positive genetic correlation between metabolic rate and growth rate. Rather, the patterns of genetic correlations suggest that genetic variance in food consumption is the single most influential trait shaping somatic growth rate, but that additional variance in growth can be explained by considering the joint effect of consumption and MR. The genetic variance in consumption and MR also translated into genetic variance in age at maturation, creating a direct link between these energy budget components and a life history trait with strong fitness effects. Moreover, a weak positive correlation between MR and food consumption suggests the presence of substantial amounts of independent genetic control of these traits, consistent with results obtained using genomic approaches.

Understanding whether populations and communities can evolve fast enough to keep up with ongoing climate change is one of the most pressing issues in biology today. A growing number of studies have documented rapid evolutionary responses to warming, suggesting that populations may be able to persist despite temperature increases. The challenge now is to better understand how species interactions, which are ubiquitous in nature, mediate these population responses to warming. Here, we use laboratory natural selection experiments in a freshwater community to test hypotheses related to how thermal evolution of Daphnia pulex to two selection temperatures (12 and 18°C) is mediated by rapid thermal evolution of its algal resource ( Scenedesmus obliquus ) or by the presence of the zooplankton predator Chaoborus americanus. We found that cold‐evolved algae (a high‐quality resource) facilitated the evolution of increased thermal plasticity in Daphnia populations selected at 12°C, for both body size and per capita growth rates ( r ). Conversely, warm‐evolved algae facilitated the evolution of increased r thermal plasticity for Daphnia selected at 18°C. Lastly, we found that the effect of selection temperature on evolved Daphnia body size was more pronounced when Daphnia were also reared with predators. These data demonstrate that trait evolution of a focal population to the thermal environment can be affected by both bottom‐up and top‐down species interactions and that rapid temperature evolution of a resource can have cascading effects on consumer thermal evolution. Our study highlights the importance of incorporating species interactions when estimating ecological and evolutionary responses of populations and communities to ongoing temperature warming.

The metabolic response of fish to exercise is highly dependent on environmental factors such as temperature. In addition to natural challenges that force exercise (foraging, avoiding predators, etc.), sportfish species are also subjected to exercise when they are hooked by anglers, leading to metabolic energy costs that may impact fitness. While several studies have examined the physiological response of fish to capture in warm conditions, little work has examined this response under cold winter conditions when fish are targeted by ice-anglers. To fill this gap, we examined the metabolic impacts of exercise duration and air exposure on bluegill, Lepomis macrochirus, at a temperature typical for ice angling. Thirty-two bluegill were subjected to a simulated angling session which included either a light (30 s) or exhaustive exercise procedure, followed by either 30 s or 4 min of air exposure. Fish were then assessed at 5 °C for the following metabolic metrics using intermittent-flow respirometry: standard metabolic rate (SMR), maximum metabolic rate (MMR), aerobic scope (AS), recovery time, and excess post-exercise oxygen consumption (EPOC). Fish exercised to exhaustion had higher EPOC compared to lightly exercised fish, however EPOC was not affected by air exposure time. No other metrics were impacted by air exposure or exercise duration. These results are directly applicable to physiological outcomes for fish captured by ice-anglers during the winter and suggest that both low temperatures and low durations of exercise serve to keep metabolic costs low for fish angled during the winter months.

Although warming and low dissolved oxygen ( DO ) levels are co‐occurring significant climatic stressors in the ocean, the combined effects of these stressors on marine benthic animals have not been well established. Here, we tested the effects of elevated temperatures and low dissolved oxygen levels on the survival, emerging behavior from sediment, and the respiration of juvenile cosmopolitan Manila clams ( Venerupis philippinarum ) by exposing them to two temperatures (20 and 23.5°C) and DO levels (3.5 and 6–7 mg/L). Although within previously described tolerable ranges of temperature and DO, this 3.5°C increase in temperature combined with a 50% decrease in DO had a devastating effect on the survival of clams (85% mortality after 8 days). The mortality of clams under normoxia at 23.5°C appeared to be higher than under the low DO condition at 20°C. On the other hand, more clams emerged from sediment under the low DO condition at 20°C than under any other conditions. Oxygen consumption rates were not significantly affected by different conditions. Our results suggest temperature elevation combined with low oxygen additively increases stress on Manila clams and that warming is at least as stressful as low DO in terms of mortality. However, low DO poses another threat as it may induce emergence from sediment, and, thus increase predation risk. This is the first evidence that a combination of warming and deoxygenation stressors should reduce population survival of clams much more so than changes in a single stressor.

Background In the wild, matrinchã (Brycon amazonicus) and tambaqui (Colossoma macropomum) rely strongly on their swimming capacity to perform feeding, migration and reproductive activities. Sustained swimming speed in fishes is performed almost exclusively by aerobic red muscles. The white muscle has high contraction power, but fatigue quickly, being used mainly in sprints and bursts, with a maximum duration of few seconds. The Ucrit test, an incremental velocity procedure, is mainly a measure of the aerobic capacity of a fish, but with a high participation of anaerobic metabolism close to the velocity of fatigue. Our previous study has indicated a high swimming performance of matrinchã (Ucrit) after hypoxia exposure, despite increased levels of lactate in plasma. In contrast, tambaqui with high lactate levels in plasma presented very low swimming performance. Therefore, we aimed to study the resistance of matrinchã and tambaqui to the increased lactate levels in muscle over an incremental velocity test (Ucrit). As a secondary aim, we analyzed the differences in anaerobic metabolism in response to environmental hypoxia, which could also support the better swimming performance of matrinchã, compared to tambaqui. Methods We measured, over incremented velocities in both species, the metabolic rate (the oxygen consumption by the fish; MO2), and the concentrations of lactate and nitrites and nitrates (NOx) in muscles. NOx was measured as an indicator of nitric oxide and its possible role in improving cardiorespiratory capacity in these fishes, which could postpone the use of anaerobic metabolism and lactate production during the swimming test. Also, we submitted fishes until fatigue and hypoxia (0.5 mg L−1) and measured, in addition to the previous parameters, lactate dehydrogenase activity (LDH; the enzyme responsible for lactate production), since that swimming performance could also be explained by the anaerobic capacity of producing ATP. Results Matrinchã exhibited a better swimming performance and higher oxygen consumption rates. Lactate levels were higher in matrinchã only at the moment of fatigue. Under hypoxia, LDH activity increased in the white muscle only in tambaqui, but averages were always higher in matrinchã. Discussion and conclusions The results suggest that matrinchã is more resistant than tambaqui regarding lactate accumulation in muscle at the Ucrit test, but it is not clear how much it contributes to postpone fatigue. The higher metabolic rate possibly allows the accumulated lactate to be used as aerobic fuel by the matrinchã, improving swimming performance. More studies are needed regarding matrinchã’s ability to oxidize lactate, the effects of exercise on muscle acidification, and the hydrodynamics of these species, to clarify why matrinchã is a better swimmer than tambaqui.

The question of who leads and who follows is crucial to our understanding of the collective movements of group‐living animals. Various characteristics associated with leadership have been documented across a range of social taxa, including hunger, motivation, dominance and personality. Comparatively little is known about the physiological mechanisms that underlie leadership. Here, we tested whether the metabolic phenotype of individual fish (x‐ray tetras, Pristella maxillaris ) determined their relative position within a moving shoal and their tendency to act as leaders. In contrast to previous work, we found that individuals with low maximal metabolic rates and low aerobic scope tended to be more likely to be found at the front of shoals and were more likely to act as leaders. We suggest that leadership by low‐performing individuals leads to greater group cohesion. However, in more challenging environmental contexts, such as flowing water, higher performing animals may be more likely to become leaders while low‐performing individuals seek the more favourable hydrodynamic conditions at the rear of the group. Hence, the travelling speed of the group may mediate the relationship between metabolic phenotype and leadership.

Polar cod, Boreogadus saida, is an important prey species in the Arctic ecosystem, yet its habitat is changing rapidly: Climate change, through rising seawater temperatures and CO2 concentrations, is projected to be most pronounced in Arctic waters. This study aimed at investigating the influence of ocean acidification and warming on maximum performance parameters of B. saida as indicators for the species’ acclimation capacities under environmental conditions projected for the end of this century. After four months at four acclimation temperatures (0, 3, 6, 8°C) each combined with two PCO2 levels (390 and 1170 µatm), aerobic capacities and swimming performance of B. saida were recorded following a Ucrit protocol. At both CO2 levels, standard metabolic rate (SMR) was elevated at the highest acclimation temperature indicating thermal limitations. Maximum metabolic rate (MMR) increased continuously with temperature, suggesting an optimum temperature for aerobic scope for exercise (ASex) at 6°C. Aerobic swimming performance (Ugait) increased with acclimation temperature irrespective of CO2 levels, while critical swimming speed (Ucrit) did not reveal any clear trend with temperature. Hypercapnia evoked an increase in MMR (and thereby ASex). However, swimming performance (both Ugait and Ucrit) was impaired under elevated near-future PCO2 conditions, indicating reduced efficiencies of oxygen turnover. The contribution of anaerobic metabolism to swimming performance was overall very low, and further reduced under hypercapnia. Our results revealed high sensitivities of maximum performance parameters (MMR, Ugait, Ucrit) of B. saida to ocean acidification. Impaired swimming capacity under ocean acidification may reflect reduced future competitive strength of B. saida.

Ocean acidification is hypothesized to limit the performance of squids due to their exceptional oxygen demand and pH-sensitivity of blood-oxygen binding, which may reduce oxygen supply in acidified waters. The critical oxygen partial pressure (Pcrit), the PO2 below which oxygen supply cannot match basal demand, is a commonly reported index of hypoxia tolerance. Any CO2-induced reduction in oxygen supply should be apparent as an increase in Pcrit. In this study, we assessed the effects of CO2 (46-143 Pa; 455-1410 μatm) on the metabolic rate and Pcrit of two squid species - Dosidicus gigas and Doryteuthis pealeii - through manipulative experiments. We also developed a model, with inputs for hemocyanin pH-sensitivity, blood PCO2, and buffering capacity that simulates blood oxygen supply under varying seawater CO2 partial pressures. We compare model outputs to measured Pcrit in squids. Using blood-O2 parameters from the literature for model inputs, we estimated that, in the absence of blood acid-base regulation, an increase in seawater PCO2 to 100 Pa (≈ 1000 μatm) would result in a maximum drop in arterial hemocyanin-O2 saturation by 1.6% at normoxia and a Pcrit increase of ≈0.5 kPa. Our live-animal experiments support this supposition, as CO2 had no effect on measured metabolic rate or Pcrit in either squid species.

Convergent evolution of a novel locomotor strategy implies that a fitness benefit may be associated with the new gait. Opportunities to study this phenomenon are often constrained by a lack of transitional taxa, but teleost fishes offer examples of extant species across such evolutionary shifts in gait. For instance, one species from Osteoglossiformes and the entire order of Gymnotiformes independently evolved a novel gait, gymnotiform locomotion, where thrust is produced by the undulation of an elongate anal fin. Here, we investigate whether this convergence in gait is also associated with similarities in shape, burst swimming abilities, and/or steady‐swimming energetics. Specifically, we measured body and fin morphology of fish within Gymnotiformes and Osteoglossiformes, along with closely related Siluriformes and Cypriniformes, to examine the link between gymnotiform locomotion and morphology in a phylogenetic context. Second, we tested the burst swimming capabilities and oxygen consumption during endurance swimming of a subset of the same gymnotiform, osteoglossiform, and cypriniform species, including “transitional” Osteoglossiformes that exhibit intermediate gaits, to determine whether the evolution of this specialized gait is associated with a change in either of these performance metrics. Our results suggest that convergence on the gymnotiform gait is associated with morphological convergence, but does not constrain a fish's maximum sprinting speeds or their energetic demands during steady swimming.

Kurt Paschke 1,2 José Agüero 3 Paulina Gebauer 4 Fernando Díaz 5 Maite Mascaró 6,7 Estefany López-Ripoll 3 Denisse Re 5 Claudia Caamal-Monsreal 6,7 Nelly Tremblay 6,8 Hans-Otto Pörtner 9 Carlos Rosas 6,7 * 1 Instituto de Acuicultura, Universidad Austral de Chile, Puerto Montt, Chile 2 Centro FONDAP de Investigación en Dinámica de Ecosistemas Marinos de Altas Latitudes (IDEAL), Punta Arenas, Chile 3 Posgrado en Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Ciudad de Mexico, Mexico 4 Centro i~mar, Universidad de Los Lagos, Puerto Montt, Chile 5 Laboratorio de Ecofisiología de Organismos Acuáticos, Departamento de Biotecnología Marina, Centro de Investigación Científica y de Educación Superior de Ensenada, Ensenada, Mexico 6 Unidad Multidisciplinaria de Docencia e Investigación, Facultad de Ciencias, Universidad Nacional Autónoma de Mexico, Sisal, Mexico 7 Laboratorio de Resiliencia Costera (LANRESC, CONACYT), Sisal, Mexico 8 Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Biologische Anstalt Helgoland, Shelf Seas Systems Ecology, Helgoland, Germany 9 Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Integrative Ecophysiology, Bremerhaven, Germany Considering that swim-flume or chasing methods fail in the estimation of maximum metabolic rate and in the estimation of Aerobic Scope (AS) of sedentary or sluggish aquatic ectotherms, we propose a novel conceptual approach in which high metabolic rates can be obtained through stimulation of organism metabolic activity using high and low non-lethal temperatures that induce high (HMR) and low metabolic rates (LMR), This method was defined as TIMR: Temperature Induced Metabolic Rate, designed to obtain an aerobic power budget based on temperature-induced metabolic scope which may mirror thermal metabolic scope (TMS = HMR—LMR). Prior to use, the researcher should know the critical thermal maximum (CT max) and minimum (CT min) of animals, and calculate temperature TIMR max (at temperatures −5–10% below CT max) and TIMR min (at temperatures +5–10% above CT min), or choose a high and low non-lethal temperature that provoke a higher and lower metabolic rate than observed in routine conditions. Two sets of experiments were carried out. The first compared swim-flume open respirometry and the TIMR protocol using Centropomus undecimalis (snook), an endurance swimmer, acclimated at different temperatures. Results showed that independent of the method used and of the magnitude of the metabolic response, a similar relationship between maximum metabolic budget and acclimation temperature was observed, demonstrating that the TIMR method allows the identification of TMS. The second evaluated the effect of acclimation temperature in snook, semi-sedentary yellow tail ( Ocyurus chrysurus ), and sedentary clownfish ( Amphiprion ocellaris ), using TIMR and the chasing method. Both methods produced similar maximum metabolic rates in snook and yellowtail fish, but strong differences became visible in clownfish. In clownfish, the TIMR method led to a significantly higher TMS than the chasing method indicating that chasing may not fully exploit the aerobic power budget in sedentary species. Thus, the TIMR method provides an alternative way to estimate the difference between high and low metabolic activity under different acclimation conditions that, although not equivalent to AS may allow the standardized estimation of TMS that is relevant for sedentary species where measurement of AS via maximal swimming is inappropriate.

Group living is widespread among animals and has a range of positive effects on individual foraging and predator avoidance. For fishes, capture by humans constitutes a major source of mortality, and the ecological effects of group living could carry‐over to harvest scenarios if fish are more likely to interact with fishing gears when in social groups. Furthermore, individual metabolic rate can affect both foraging requirements and social behaviors, and could, therefore, have an additional influence on which fish are most vulnerable to capture by fishing. Here, we studied whether social environment (i.e., social group size) and metabolic rate exert independent or interactive effects on the vulnerability of wild zebrafish ( Danio rerio ) to capture by a baited passive trap gear. Using video analysis, we observed the tendency for individual fish to enter a deployed trap when in different shoal sizes. Fish in larger groups were more vulnerable to capture than fish tested individually or at smaller group sizes. Specifically, focal fish in larger groups entered traps sooner, spent more total time within the trap, and were more likely to re‐enter the trap after an escape. Contrary to expectations, there was evidence that fish with a higher SMR took longer to enter traps, possibly due to a reduced tendency to follow groupmates or attraction to conspecifics already within the trap. Overall, however, social influences appeared to largely overwhelm any link between vulnerability and metabolic rate. The results suggest that group behavior, which in a natural predation setting is beneficial for avoiding predators, could be maladaptive under a trap harvest scenario and be an important mediator of which traits are under harvest associated selection.

The lumpfish (Cyclopterus lumpus) is a semi-pelagic globiform teleost native to the North Atlantic with a ventral suction disc that allows for attachment onto surfaces. Some local populations are in decline and the species has recently become important in salmonid sea cages as cleaner fish. Little is known about the basal physiology of the lumpfish, and a characterization of thermal performance, aerobic capacity, swimming behaviour and stress response is therefore warranted. In the present study, swim tunnel respirometry was performed on lumpfish acclimated to 3, 9 or 15°C. Higher temperatures were also attempted, but at 18°C their behaviour became erratic and 15% of the fish died over 3 weeks of acclimation. Water current tolerance was assessed in two size classes (∼75g and∼300g) both with and without the ability to voluntarily use the ventral suction disc. Lastly, blood samples were taken from resting, exhausted and recovered fish to assess haematological effects of exercise stress. Lumpfish had relatively low aerobic scopes that increased slightly with temperature. Critical swimming speed was poor, increasing within the tested temperatures from 1.3 to 1.7 body lengths s−1 in 300 g fish. They struggled to remain sucked onto surfaces at currents above 70−110 cm s−1, depending on size. Acute stress effects were modest or non-existent in terms of changes in cortisol, lactate, glucose, erythrocytes and ion balance. These results describe a typical sluggish and benthic species, which is contradictory to the pelagic nature of lumpfish in large parts of its lifecycle.

The potential benefits of a commercial preparation of heptanoate (NOREL, HEPTON®) were evaluated in an 11‐week gilthead sea bream feeding trial (May–August), using a factorial design with four isoproteic and isoenergetic diets. Fish meal (FM) was added at 200 g/kg in D1–D2 diets and at 50 g/kg in D3–D4 diets, which also contained fish peptones and plant proteins as source of proteins. Heptanoate was added at 3 g/kg in D2 and D4 diets. All fish grew from 13–14 g to 81–84 g with an overall feed efficiency (FE) of 0.91–0.94. An early impairment of FE (weeks 1–4) was found with the standard FM‐based diet (D1), but this detrimental condition was reversed by heptanoate, increasing FE from 0.88 in D1 fish to 0.99 in D2 fish. Further improvements were progressively diluted over time, remaining D2 and D3–D4 fed fish almost undistinguishable through all the trial. Heptanoate supplementation produced higher hepatic glycogen depots, but no signs of histopathological damage were found in liver or intestine. Other lasting heptanoate effects included changes in plasma antioxidant capacity, plasma cortisol and growth hormone levels, and measures of respirometry in swimming performance tests. Altogether, it supports the potential use of heptanoate to speed up adaptive and healthy metabolic states of farmed fish to cope with challenging culture conditions.

The invasion of land required amphibious fishes to evolve new strategies to avoid toxic ammonia accumulation in the absence of water flow over the gills. We investigated amphibious behaviour and nitrogen excretion strategies in six phylogenetically diverse Aplocheiloid killifishes ( Anablepsoides hartii, Cynodonichthys hildebrandi, Rivulus cylindraceus, Kryptolebias marmoratus, Fundulopanchax gardneri, and Aplocheilus lineatus ) in order to determine if a common strategy evolved. All species voluntarily emersed (left water) over several days, and also in response to environmental stressors (low O 2, high temperature). All species were ammoniotelic in water and released gaseous ammonia (NH 3 volatilization) during air exposure as the primary route for nitrogen excretion. Metabolic depression, urea synthesis, and/or ammonia accumulation during air exposure were not common strategies used by these species. Immunostaining revealed the presence of ammonia-transporting Rhesus proteins (Rhcg1 and Rhcg2) in the skin of all six species, indicating a shared mechanism for ammonia volatilization. We also found Rhcg in the skin of several other fully aquatic fishes, implying that cutaneous ammonia excretion is not exclusive to amphibious fishes. Overall, our results demonstrate that similar nitrogen excretion strategies while out of water were used by all killifish species tested; possibly the result of shared ancestral amphibious traits, phenotypic convergence, or a combination of both.

Temperature fluctuations have caused considerable biological and ecological impacts on marine organisms and their communities. For example, increased temperatures in sub-tropical environments have led to the influx of tropical “vagrant” marine species into cooler temperate waters in a phenomenon called ‘tropicalisation’. Here we combine metabolic performance metrics, feeding manipulations and nutritional geometry models to examine the influence of temperature on macronutrient selection (energy amounts of protein, lipid and carbohydrates) in the Indo-Pacific damselfish Abudefduf vaigiensis and explore the role of temperature and macronutrient intake on individual performance (active and routine metabolic rate, and burst swim speed). Indo-pacific damselfish fed non-randomly from presented food blocks, showing selection for their macronutrient intake. In our high-temperature treatment we observed a significant increase in the intake of protein and lipid, but not carbohydrate. The fish in our low-temperature treatment had a significantly higher active metabolic rate and burst swim speed compared to our high-temperature treatment. Our findings provide evidence that the vagrant Indo-Pacific Damselfish in Sydney are able to select specific macronutrients in their diets ameliorating the effects on performance when thermally stressed. This work also suggests some underlying level of acclimation to or selection for colder water temperatures in these relatively recently recruited fish. Further studies should benefit from the approach proposed here, to better understand the ecological and evolutionary drivers that influence the survival of tropical species in marginal thermal habitats.

Two dominant krill species Meganyctiphanes norvegica (Sars, 1857) and Thysanoessa raschii (Sars, 1864) coexist in the subarctic waters of lower St. Lawrence Estuary, Canada. Both species perform diel vertical migrations representing often large displacements of ~100–150 m through several temperature regimes. We studied the impact of temperature, a fundamental factor controlling the metabolism of ectothermic species, on the metabolic rate and swimming activity of the two species. Annular respirometers were used to quantify simultaneously oxygen consumption (ṀO2 g–1 wet mass) and the spontaneous swimming activity of individual krill over a period of 24 h at six temperatures, by intermittent-flow respirometry. Both species significantly increased their low routine and maximal metabolic rates from 0 °C to 15 °C, suggesting high thermal plasticity. The spontaneous swimming activity of M. norvegica was reduced to almost zero at 0 °C, whereas T. raschii swam 1.0 cm s–1 at this temperature. Based on swimming performance, M. norvegica might avoid the cold intermediate layer (CIL, < 1 °C) in the estuary, which coincides with actual daytime distribution below the CIL in the warmer deep-water layer. Despite the rare occurrence of 15 °C in the estuary, both species still showed high metabolic and swimming performance at that temperature. High and differential thermal plasticity of both krill species might have important ecological consequences for their distribution patterns in their natural environment, as energy requirements differ in the two species.

We reared Cloeon dipterum from egg hatch to adult at 10 constant temperatures (12.1–33.5°C) to test 3 hypotheses (thermal equilibrium hypothesis, temperature size rule [TSR], and O2- and capacity-limited thermal tolerance [OCLTT]) that account for variation in life-history traits across thermal gradients. Male and female adult size declined ~67 and 78% and larval development time declined ~88% with warming; chronic survivorship (thermal limit for population growth) was highest from 16.2 to 23.9°C (mean = 85%) and declined to 0 at 33.5°C; thresholds for 0 growth and development were 10.0 and 10.7°C, respectively; peak rate of population increase (r) occurred at 27.8°C; rates of growth and development were maximal at 30°C; fecundity was greatest at 12.1°C; and between 14.3 and 30°C, growth and development rates increased linearly and the number of degree days (>10.7°C) to complete development was nearly constant (mean = 271). Acute survivorship during short-term thermal ramping was 0 at 40°C. Warming temperature caused development rate to increase proportionately faster than growth rate; male and female adult size to decrease as per TSR, with adult females ~5× larger at 12.1 than 31.7°C; adult size to decrease proportionately more for females than males; and fecundity to decrease proportionately more than adult female size. TSR was related to differences in the responses of growth and development rates at temperatures above thresholds rather than to thresholds for growth or development per se. Respirometry suggested that OCLTT is more applicable to acute than chronic thermal limits. Cloeon dipterum appears to have a thermal 'acclimation zone' between 14.3 and 30°C where development and growth rates change linearly and degree-day requirements to complete metamorphosis are constant. The optimum temperature is ~27.8°C where r is maximum. We propose 5 hypotheses to explain these patterns.

Lake sturgeon (Acipenser fulvescens) occupy some of the most northerly distributions of any sturgeon species and experience extended overwintering periods when resources may be limited. Conservation stocking is currently used as a management tool to enhance lake sturgeon populations that are at risk or endangered. One of the most limiting components of the conservation effort is our understanding of energy requirements that allow age-0 lake sturgeon to survive their first winter. In this study, age-0 fish (mean mass 5.6 g ± 0.5 S.E.; mean total length 12.7 cm ± 0.4 S.E.) were held in groups of 12 individuals (10 total groups) and starved for a period of four weeks while being held at 1 ± 1 °C. This setting was intended to simulate winter conditions that occur in the Winnipeg River, MB, Canada. Post-winter fish condition and physiology were compared to pre-winter fish using survival, energy density, metabolic rate, glucose, triglyceride, protein, and cortisol production as metrics. While mortality was high (42%) during the experiment, results indicated that fish with total water content below 90% and energy density above 2000 J/g were more likely to survive. Whole body triglyceride, plasma triglyceride, plasma glucose levels, and standard metabolic rates were also found to significantly decline over time while whole body cortisol concentration increased. Understanding these thresholds will help in future refinements of rearing conditions, which look to improve the survival of age-0 lake sturgeon released into the wild pre-winter.

Amphibious fishes moving over land between aquatic habitats likely encounter abrupt changes in a number of environmental conditions, including salinity. This study characterized the 1) spatial heterogeneity in salinity in the mangrove forest habitat of the self-fertilizing, amphibious mangrove rivulus (Kryptolebias marmoratus), 2) metabolic cost and behavioral response to acute exposure to novel salinity, and 3) repeatability of individual responses to acute changes in salinity. In mangrove habitats on Long Caye, Belize, salinity varied widely over short distances from 20.9–41.7‰ over a 90 cm distance. In the lab, fish were exposed to an acute change in salinity of Δ10, 20, or 30‰. Oxygen consumption significantly decreased in response to a 10‰ decrease in salinity and increased when salinity was elevated by 30‰. Activity levels significantly increased with an increase in salinity (Δ20 and 30‰). Individuals showed repeatable differences in both oxygen consumption rates and activity levels. Together, our data show that K. marmoratus is highly responsive to abrupt increases in salinity. Thus, movements made by K. marmoratus between temporary pools in the mangrove forest will acutely alter behavior and possibly metabolism, with many potential ecological consequences.

Bitterling fishes and unionid mussels are involved in a two-sided co-evolutionary association. On the one side, bitterling exploit unionids by ovipositing in their gills. On the other side, unionids develop via a larval stage (glochidium) that attaches to fish gills. Both interactions are parasitic and expected to have negative consequences for the host. Here, we examine the effects of this association on the metabolic rates of mussel and fish hosts by measuring oxygen uptake rates (MO2). Measurements were performed on two widespread and broadly coexisting species, namely the rose bitterling Rhodeus ocellatus and Chinese pond mussel Sinanodonta woodiana. As predicted, we observed an increase in routine MO2 in mussels parasitized by bitterling, but only when hosting early stages of bitterling embryos that reside in the interlamellar space of the gills and obstruct water circulation. Hosting later-stage bitterling embryos (that reside in the suprabranchial cavity outside the host gills) was not associated with a higher routine MO2. We did not observe an acute negative effect of glochidial infestations on maximal oxygen uptake rate (MO(2)max), but glochidia-infested bitterling showed consistently lower oxygen consumption rates during recovery from MO(2)max. Our results suggest that acute costs of this mutually parasitic relationship might be mitigated, at least in part, by adaptations to limit infestation rates.

Adult males of Calanus copepods in the Arctic are mainly observed between late autumn and late spring, and are seldom recorded during summer. Due to logistical constraints, there are still relatively few studies on zooplankton in high-latitude regions during the winter, and subsequently, little is known about Calanus males. Here, we present data on abundance, spatial distribution, prosome length, lipid content, respiration and swimming activity of i>Calanus adults, along with adult sex ratios in i>Calanus populations from 5 Arctic fjords in Svalbard, Norway (78-80° N) during the polar night in January 2015, 2016 and 2017. Adult males and females of i>Calanus were observed at all locations and occurred throughout the entire water column. Morphological examination and molecular identification of i>Calanus males proved that all males encountered belong to Calanus glacialis, even in the fjords where overwintering copepodite stage CV of C. finmarchicus dominated at the time. Adult sex ratios in C. glacialis populations varied from 1 male per 4 females to 2 males per female. From 3 to 18% of females carried spermatophores attached to the genital segment. Lipid content in males was slightly higher than in females. Shipboard experiments showed that males had higher swimming activity and respiration rates than females. Our observations indicate that adult males of C. glacialis stay active and demonstrate active mating behavior in mid-winter, and that the mating phenology of C. glacialis is decoupled from that of C. finmarchicus in the study area in January.

Volatile organic compounds (VOCs) are known to potentially cause a severe change in the respiratory metabolism of freshwater species, however the effect of these contaminants on groundwater-obligate species has not been investigated to date. Tetrachloroethylene (TCE) is a VOC frequently found in the groundwater bodies of industrialized areas, even years after a contamination event because TCE degradation takes several decades to occur. Contamination from TCE is considered persistent and difficult to remediate. Its high density favors a gravity-driven vertical infiltration into groundwater bodies. The TCE threshold value is 1.1 μg/L in groundwater bodies of Italy. TCE concentration in many Italian groundwater bodies is widely over this legal limit. In this study, we investigated the effect of 1.1 μg/L TCE on the survival, oxygen consumption, and locomotory activities of a groundwater-obligate copepod species. The specimens required for the trials were collected in the Antro del Corchia Cave (Tuscany). We measured the individual-based oxygen consumption of this species as a proxy of possible metabolic reactions to long-term (5 days) exposures to TCE at 8.0°C that is the mean annual temperature of groundwater flowing in the cave. To this end, we used a sealed glass microplate equipped with 24-planar oxygen sensor spots with optical isolation glued onto the bottom of 80-μL wells (Loligo Systems, Denmark) integrated with a 24-channel fluorescence-based respirometry system (SDR Sensor Dish Reader, PreSens, Germany). The system allows simultaneous measurement of 20 replicates and 4 controls. Survival and locomotory activity assessments were performed by counting the number of alive individuals and measuring the number of moving animals in 5 mL glass vials each containing 20 individuals. Preliminary results showed a decreasing in oxygen consumption of the organisms exposed to 1.1 μg/L TCE for 5 days at 8°C respect to the control. However, neither survival nor locomotory activities appeared to have been affected by exposure to TCE. See Suppl. material 1.

The pace-of-life syndrome (POLS) concept predicts that individuals with high baseline metabolic rates demonstrate high boldness, aggressiveness, and activity, especially in food acquisition, with associated relatively greater energy requirements. In fishes, these behaviors may increase individual vulnerability to angling. To test the predictions of the POLS concept, we quantified individual standard metabolic rate (SMR) and boldness in both wild-caught and hatchery-reared Eurasian perch (Perca fluviatilis). We found both SMR and boldness to be repeatable traits but detected no correlation between them. Individual vulnerability to angling was assessed in the hatchery-reared perch, but we found no difference in boldness or SMR between vulnerable and nonvulnerable perch. Wild-caught perch were ice fished using either natural or artificial bait, and we observed no differences in boldness or SMR with respect to bait type or capture order. Our findings do not support the predictions of the POLS concept and, consistent with earlier studies in perch, suggest that angling may not drive selection against boldness in this species.

Mangrove forests are amongst the tropical marine ecosystems most severely affected by rapid environmental change, and the activities of key associated macrobenthic species contribute to their ecological resilience. Along the east coast of Africa, the amphibious sesarmid crab Neosarmatium africanum (=meinerti) plays a pivotal role in mangrove ecosystem functioning through carbon cycling and sediment bioturbation. In the face of rapid climate change, identifying the sensitivity and vulnerability to global warming of this species is of increasing importance. Based on a latitudinal comparison, we measured the thermal sensitivity of a tropical and a temperate population of N. africanum, testing specimens at the centre and southern limit of its distribution, respectively. We measured metabolic oxygen consumption and haemolymph dissolved oxygen content during air and water breathing within a temperature range that matched the natural environmental conditions. The results indicate different thermal sensitivities in the physiological responses of N. africanum from tropical and temperate populations, especially during air breathing. The differences observed in the thermal physiology between the two populations suggest that the effect of global warming on this important mangrove species may be different under different climate regimes.

Understanding how the current warming trends affect fish populations is crucial for effective conservation and management. To help define suitable thermal habitat for juvenile Chinook salmon, the thermal performance of juvenile Chinook salmon acclimated to either 15 or 19°C was tested across a range of environmentally relevant acute temperature changes (from 12 to 26°C). Swim tunnel respirometers were used to measure routine oxygen uptake as a measure of routine metabolic rate (RMR) and oxygen uptake when swimming maximally as a measure of maximal metabolic rate (MMR) at each test temperature. We estimated absolute aerobic scope (AAS = MMR - RMR), the capacity to supply oxygen beyond routine needs, as well as factorial aerobic scope (FAS = MMR/RMR). All fish swam at a test temperature of 23°C regardless of acclimation temperature, but some mortality occurred at 25°C during MMR measurements. Overall, RMR and MMR increased with acute warming, but aerobic capacity was unaffected by test temperatures up to 23°C in both acclimation groups. The mean AAS for fish acclimated and tested at 15°C (7.06 ± 1.76 mg O 2 kg -1 h -1 ) was similar to that measured for fish acclimated and tested at 19°C (8.80 ± 1.42 mg O 2 kg -1 h -1 ). Over the entire acute test temperature range, while MMR and AAS were similar for the two acclimation groups, RMR was significantly lower and FAS consequently higher at the lower test temperatures for the fish acclimated at 19°C. Thus, this stock of juvenile Chinook salmon shows an impressive aerobic capacity when acutely warmed to temperatures close to their upper thermal tolerance limit, regardless of the acclimation temperature. These results are compared with those for other salmonids, and the implications of our findings for informing management actions are discussed.

Oxygen availability is key in determining habitat suitability for marine fish. As a result of climate change, low oxygen conditions are predicted to occur more frequently and over a greater geographic extent. Studies assessing the long-term chronic effects and impacts for commercially important fish are rare. To assess the potential effects of climate-induced low oxygen on fisheries, physiological data, such as critical thresholds, derived from laboratory experiments on 5 commercial fish species were integrated with hindcast and future oxygen projections from the hydrodynamic-biogeochemical model GETM-ERSEM. By using this approach, changes in habitat suitability from the 1970s to 2100 were identified. In the North Sea, the current extent of areas with the lowest oxygen levels is smaller than during the 1970s, with improved oxygen conditions having less impact on species’ critical thresholds. Oxygen levels are expected to decrease again in the coming century due to climate change, although not to the minima of previous decades. In affected areas and years, intermediate oxygen levels could have temporary impacts in late summer on swimming, growth, ingestion and metabolic scope of adult fish. These results demonstrate that although physical model oxygen projections help to provide insight, they are insufficient by themselves to predict the full potential impacts of climate change on fish distribution and fisheries. Such modelling requires underpinning through experimentation, particularly of the physiological effects of climate change on different life stages so that effects on reproduction, growth and commercial catches can be determined and tailored, and robust management measures put in place.

There is currently only a limited understanding of the relationship between water quality and predation on Pacific salmon Oncorhynchus spp. smolts. We addressed the hypothesis that poor water quality will decrease a smolt's swimming performance and presumably its predator evasion capabilities. Predation is a major factor affecting salmon smolt survival throughout the San Joaquin River and the Sacramento–San Joaquin Delta of California. Prior studies have quantified predation rates, but the effect of water quality on predator evasion capability has not previously been evaluated. We quantified the swimming performance of juvenile Chinook Salmon O. tshawytscha in relation to water quality variables. The maximum swim speeds ( U max ) of 45 hatchery‐reared smolts (7.1–9.9 cm FL) were measured in controlled (laboratory) and field environments by using a mobile swim tunnel respirometer; measurements were obtained before and after the fish received a 2‐d exposure to the lower San Joaquin River while being held in flow‐through cages. To sample across a diversity of environmental conditions, we conducted trials during a 6‐week period that coincided with the peak smolt out‐migration. Regression models were constructed to evaluate relationships between swimming performance and four water quality covariates (water temperature, turbidity, dissolved oxygen, and conductivity). We found negative relationships between U max and both temperature and turbidity, and we described these relationships graphically. Our findings suggest that water quality management strategies with the potential to improve salmon smolt survival include managing temperatures and suspended sediment concentrations to optimize the swimming capacity of migrating smolts and possibly improve their ability to evade predators. Received July 12, 2016; accepted December 6, 2016 Published online February 21, 2017

Benzo[a]pyrene (B[a]P) is a well-known genotoxic polycylic aromatic compound whose toxicity is dependent on signaling via the aryl hydrocarbon receptor (AHR). It is unclear to what extent detrimental effects of B[a]P exposures might impact future generations and whether transgenerational effects might be AHR-dependent. This study examined the effects of developmental B[a]P exposure on 3 generations of zebrafish. Zebrafish embryos were exposed from 6 to 120h post fertilization (hpf) to 5 and 10μM B[a]P and raised in chemical-free water until adulthood (F0). Two generations were raised from F0 fish to evaluate transgenerational inheritance. Morphological, physiological and neurobehavioral parameters were measured at two life stages. Juveniles of the F0 and F2 exhibited hyper locomotor activity, decreased heartbeat and mitochondrial function. B[a]P exposure during development resulted in decreased global DNA methylation levels and generally reduced expression of DNA methyltransferases in wild type zebrafish, with the latter effect largely reversed in an AHR2-null background. Adults from the F0 B[a]P exposed lineage displayed social anxiety-like behavior. Adults in the F2 transgeneration manifested gender-specific increased body mass index (BMI), increased oxygen consumption and hyper-avoidance behavior. Exposure to benzo[a]pyrene during development resulted in transgenerational inheritance of neurobehavioral and physiological deficiencies. Indirect evidence suggested the potential for an AHR2-dependent epigenetic route.

The occurrence of Asiatic Weatherfish, Misgurnus anguillicaudatus, in Alabama, a state known for its rich biodiversity, has generated concern among conservation managers. The current study used respirometry techniques to investigate the effects of increasing temperature on four native southeastern fishes (one cyprinid, two percids, and one elassomid) and the non-native M. anguillicaudatus. A minimum of five individuals of each species were used, and three experimental temperatures were chosen to represent spring and summer averages of northeast Alabama streams (15, 20, and 25°C). Overall, mean standard metabolic rates (SMRs) for M. anguillicaudatus were low (97.01, 127.75, and 158.50 mg O2 kg-1h-1 at 15, 20, and 25°C, respectively); M. anguillicaudatus was the only species for which SMR did not significantly increase with temperature (p = 0.467). In contrast, mean SMRs for all native species examined were higher than M. anguillicaudatus rates at a given temperature, and mean SMRs for Cyprinella caerulea, Etheostoma brevirostrum, and Etheostoma ditrema exhibited significant increases in SMR when temperatures were increased (e.g. 403.46, 704.42, and 1150.03 mg O2 kg-1h-1 at 25°C, respectively) (p < 0.01). Elassoma zonatum displayed highly significant increases in SMR when temperature increased from 15-20°C (p < 0.001). Overall, the abiotic tolerances of M. anguillicaudatus may facilitate further establishment that could lead to negative impacts on native species.

River modifications have altered critical habitats for fishes at a variety of spatial scales and caused global declines of many fluvial species. At small spatial scales (<1 m 2 ), alluvial sand dunes, a ubiquitous habitat in highly modified rivers, are thought to provide energetic relief for benthic fishes in energetically costly riverine landscapes created by water flow. However, use of alluvial dune habitat is not well understood, and it is unclear whether dunes provide refuge that effectively reduces energetic costs. We designed a scale‐relevant experiment to examine the energetic responses associated with sand dune habitat in rivers. We tested whether the US federally endangered pallid sturgeon ( Scaphirhynchus albus ), a benthic fish commonly associated with sand dunes, experienced reduced energetic costs with different configurations of simulated sand dune habitat. We quantified mass specific oxygen consumption ( M O 2; mg O 2 kg −1 h −1 ) using intermittent flow‐through respirometry for age‐0 sturgeon (140–170 mm) in front of a sand dune, behind a sand dune and in the absence of a sand dune at two velocities (25 and 50 cm s −1 ) commonly observed in field studies of sturgeon habitat use. Sturgeon displayed distinct station holding behaviours for each habitat configuration. Dune location did not affect energy expenditure, but sturgeon M O 2 was on average 16–20% higher in the absence of a sand dune depending on dune configuration. M O 2 was on average 14% higher at 50 cm s −1 compared with 25 cm s −1. Our results provide a potential mechanism for over two decades of research on why sturgeon and other benthic fishes exhibit selection for sand dune habitat in large rivers. Fishes that select main channel habitats may depend on energetic relief provided by sand dunes, especially when other forms of structure are not available. For this reason, alluvial sand dune habitat may be important to the persistence of benthic fishes in high flow environments. Copyright © 2017 John Wiley & Sons, Ltd.

Non-indigenous species (NIS) can impact marine biodiversity and ecosystem structure and function. Once introduced into a new region, secondary dispersal is limited by the physiology of the organism in relation to the ambient environment and by complex interactions between a suite of ecological factors such as presence of predators, competitors, and parasites. Early prediction of dispersal potential and future ‘area of impact’ is challenging, but also a great asset in taking appropriate management actions. Aerobic scope (AS) in fish has been linked to various fitness-related parameters, and may be valuable in determining dispersal potential of aquatic invasive species in novel environments. Round goby, Neogobius melanostomus, one of the most wide-ranging invasive fish species in Europe and North America, currently thrives in brackish and fresh water, but its ability to survive in high salinity waters is unknown to date. We show that AS in round goby is reduced by 30% and blood plasma osmolality increased (indicating reduced capacity for osmoregulation) at salinities approaching oceanic conditions, following slow ramping (5 PSU per week) and subsequent long-term acclimation to salinities ranging between 0 and 30 PSU (8 days at final treatment salinities before blood plasma osmolality measurements, 12–20 additional days before respirometry). Survival was also reduced at the highest salinities yet a significant proportion (61%) of the fish survived at 30 PSU. Reduced physiological performance at the highest salinities may affect growth and competitive ability under oceanic conditions, but to what extent reduced AS and osmoregulatory capacity will slow the current 30 km year-1 rate of advance of the species through the steep salinity gradient from the brackish Baltic Sea and into the oceanic North Sea remains speculative. An unintended natural experiment is in progress to test whether the rate of advance slows down. At the current rate of advance the species will reach the oceanic North Sea by 2018/2019, therefore time for taking preventative action is short.

The high prevalence of zinc deficiency is a global public health concern, and suboptimal maternal zinc consumption has been associated with adverse effects ranging from impaired glucose tolerance to low birthweights. The mechanisms that contribute to altered development and poor health in zinc deficient offspring are not completely understood. To address this gap, we utilized the Danio rerio model and investigated the impact of dietary zinc deficiency on adults and their developing progeny. Zinc deficient adult fish were significantly smaller in size, and had decreases in learning and fitness. We hypothesized that parental zinc deficiency would have an impact on their offspring’s mineral homeostasis and embryonic development. Results from mineral analysis showed that parental zinc deficiency caused their progeny to be zinc deficient. Furthermore, parental dietary zinc deficiency had adverse consequences for their offspring including a significant increase in mortality and decreased physical activity. Zinc deficient embryos had altered expression of genes that regulate metal homeostasis including several zinc transporters (ZnT8, ZnT9) and the metal-regulatory transcription factor 1 (MTF-1). Zinc deficiency was also associated with decreased expression of genes related to diabetes and pancreatic development in the embryo (Insa, Pax4, Pdx1). Decreased expression of DNA methyltransferases (Dnmt4, Dnmt6) was also found in zinc deficient offspring, which suggests that zinc deficiency in parents may cause altered epigenetic profiles for their progeny. These data should inform future studies regarding zinc deficiency and pregnancy and suggest that supplementation of zinc deficient mothers prior to pregnancy may be beneficial. Keywords: Zebrafish, zinc deficiency, epigenetics, zinc homeostasis, fitness, learning

This study aimed to assess the extent to which chasing, handling and confining Oncorhynchus mykiss to a small respirometer chamber during respirometric experiments is stressful and affects metabolic measurements. The study observed increased cortisol levels in animals tested using a chase protocol and subsequent intermittent‐flow respirometry, suggesting that this procedural treatment may stress animals.

This study examined thermally driven changes in swimming performance and aerobic metabolism ( Q 10 and aerobic scope of activity) of adult King George whiting Sillaginodes punctatus to the coldest (16° C) and the warmest (26° C) temperature encountered by this species. Compensation of aerobic scope, higher maximal swimming speeds and a maintained capacity to repay oxygen debt indicate that this species is capable of thermal acclimation to conditions expected under global warming.

The present study examined how the expression of enhanced green fluorescent protein (eGFP) and human cardiac actin (ACTC) in zebrafish Danio rerio influences embryonic heart rate ( R H ) and the swim performance and metabolic rate of adult fish. Experiments with the adults involved determining the critical swimming speed ( U crit, the highest speed sustainable and measure of aerobic capacity) while measuring oxygen consumption. Two different transgenic D. rerio lines were examined: one expressed eGFP in the heart ( tg(cmlc:egfp) ), while the second expressed ACTC in the heart and eGFP throughout the body ( tg(cmlc:actc,ba:egfp) ). It was found that R H was significantly lower in the tg(cmlc:actc,ba:egfp) embryos 4 days post‐fertilization compared to wild‐type (WT) and tg(cmlc:egfp). The swim experiments demonstrated that there was no significant difference in U crit between the transgenic lines and the wild‐type fish, but metabolic rate and cost of transport (oxygen used to travel a set distance) was nearly two‐fold higher in the tg(cmlc:actc,ba:egfp) fish compared to WT at their respective U crit. These results suggest that the expression of ACTC in the D. rerio heart and the expression of eGFP throughout the animal, alters cardiac function in the embryo and reduces the aerobic efficiency of the animal at high levels of activity.

Differences in behavior and physiology amongst individuals often alter relative fitness levels in the environment. However, the ideal behavioral/physiological phenotype in a given environment may be altered by human activity, leading to an evolutionary response in the affected population. One example of this process can be found in fisheries (including recreational freshwater fisheries), where selective capture and harvest of individuals with certain phenotypes can drive evolutionary change. While some life history traits and behavioral tendencies influencing capture likelihood have been studied, the physiological mechanisms driving this vulnerability remain poorly understood. To address this, we assessed how two major physiological characteristics (hormonal responsiveness to stress and metabolic phenotype) and one behavioral characteristic (boldness) impact the likelihood of an individual being captured by anglers. Largemouth bass, Micropterus salmoides, derived from a population artificially selected for differential angling vulnerability were assessed for boldness and for stress responsiveness (as indicated by plasma cortisol levels) following an air-exposure challenge. Largemouth bass were then stocked into a pond where experimental angling trials took place, and a subset of captured and uncaptured fish were afterwards assessed for metabolic phenotype. The results showed that stress responsiveness was the primary driver of angling vulnerability, with individuals that experienced lower rises in cortisol following the air-exposure challenge more likely to be captured. Neither boldness nor metabolic phenotype influenced capture probability. The results from this study indicate that fisheries-induced selective pressure may act on physiology, potentially altering stress responsiveness and its associated behaviors in populations exploited by recreational anglers.

Ocean warming, eutrophication and consequent decrease in oxygen lead to smaller average fish size. Although such responses are well-known in an evolutionary context, involving multiple generations, it appears to be incompatible with current rapid environmental change. Rather, phenotypic plasticity could provide a means for marine fish to cope with rapid environmental changes. However, little is known about the mechanisms underlying plastic responses to environmental conditions that favour small phenotypes.

Human alteration of thermal regimes of freshwater ecosystems is creating an urgent need to understand how freshwater ectotherms will fare under different thermal futures. Two key questions are: 1) how well do the fundamental thermal niches of ectotherms map to their realized thermal niches, and 2) which axes of the fundamental thermal niche must be modeled to predict temperature-dependent fitness in real ecosystems? The first question is particularly challenging in riverine systems, where gradients in temperature are strongly confounded by gradients in other biotic and abiotic drivers. To address these questions, we compared the realized and fundamental thermal niches of 2 congeneric riverine fish: Gadopsis marmoratus and Gadopsis bispinosus. We characterized their realized thermal niches by examining their distributions in relation to environmental temperature at multiple scales. We characterized their fundamental thermal niches by doing laboratory experiments on the thermal sensitivity of swimming performance and metabolic rates, particularly aerobic scope. The distributions of the 2 species supported the idea that they have different realized thermal niches, with G. bispinosus occupying cooler habitats than G. marmoratus. Despite this, we detected no significant differences in the shapes of thermal performance curves defining 2 axes of their fundamental niches: swimming performance and aerobic scope. Our results suggest that either the distributions of these 2 species are driven by factors other than temperature or that swimming performance and aerobic scope were not suitable proxies of their fundamental thermal niches. Our study shows that modeling the thermal niches of ectotherms along the river continuum is not straightforward. If we are to forecast effects of thermal futures effectively and efficiently, we must do more to decipher the relative influence of temperature and other abiotic drivers on the fitness of riverine ectotherms.

The effects of acclimation temperature (15, 20, 25 °C) on routine oxygen consumption and post-exercise maximal oxygen consumption rates (MO2) were measured in juvenile shortnose sturgeon (Acipenser brevirostrum LeSueur, 1818). The routine MO2 of shortnose sturgeon increased significantly from 126.75 mg O2 h−1 kg−1 at 15 °C to 253.13 mg O2 h−1 kg−1 at 25 °C. The temperature coefficient (Q 10) values of the routine metabolic rates ranged between 1.61 and 2.46, with the largest Q 10 values occurring between 15 and 20 °C. The average post-exercise MO2 of all temperature groups increased to a peak value immediately following the exercise, with levels increasing about 2-fold among all temperature groups. The Q 10 values for post-exercise MO2 ranged from 1.21 to 2.12, with the highest difference occurring between 15 and 20 °C. Post-exercise MO2 values of shortnose sturgeon in different temperature groups all decreased exponentially and statistically returned to pre-exercise (resting) levels by 30 min at 15 and 20 °C and by 60 min at 25 °C. The aerobic metabolic scope (post-exercise maximal MO2-routine MO2) increased to a maximum value ∼156 mg O2 h−1 kg−1 at intermediate experimental temperatures (i.e., 20 °C) and then decreased as the temperature increased to 25 °C. However, this trend was not significant. The results suggest that juvenile shortnose sturgeon show flexibility in their ability to adapt to various temperature environments and in their responses to exhaustive exercise.

Rainbow trout Oncorhynchus mykiss (~ 180 g, 16 °C and < 5 kg m−3) that were feed deprived and kept in total darkness showed a significant increase in critical swimming speed (U crit) between 1 and 12 days of deprivation (from 3.35 to 4.46 body length (BL) s−1) with no increase in maximum metabolic rate (MMR). They also showed a significant decrease in the estimated metabolic rate at 0 BL s−1 over 12 days which leads to a higher factorial aerobic metabolic scope at day 12 (9.38) compared to day 1 (6.54). Routine metabolic rates were also measured in ~ 90 g rainbow trout that were swimming freely in large circular respirometers at 16 °C. These showed decreasing consumption oxygen rates and reductions in the amount of oxygen consumed above standard metabolic rate (a proxy for spontaneous activity) over 12 days, though this happened significantly faster when they were kept in total darkness when compared to a 12:12-h light–dark (LD) photoperiod. Weight loss during this period was also significantly reduced in total darkness (3.33% compared to 4.98% total body weight over 12 days). Immunological assays did not reveal any consistent up- or downregulation of antipathogenic and antioxidant enzymes in the serum or skin mucus of rainbow trout between 1 and 12 days of feed and light deprivation. Overall, short periods of deprivation do not appear to significantly affect the performance of rainbow trout which appear to employ a behavioural energy-sparing strategy, albeit more so in darkness than under a 12:12-h LD regime.

Anthropogenic stressors, including pollutants, are key evolutionary drivers. It is hypothesized that rapid evolution to anthropogenic changes may alter fundamental physiological processes (e.g., energy metabolism), compromising an organism's capacity to respond to additional stressors. The Elizabeth River (ER) Superfund site represents a "natural-experiment" to explore this hypothesis in several subpopulations of Atlantic killifish that have evolved a gradation of resistance to a ubiquitous pollutant-polycyclic aromatic hydrocarbons (PAH). We examined bioenergetic shifts and associated consequences in PAH-resistant killifish by integrating genomic, physiological, and modeling approaches. Population genomics data revealed that genomic regions encoding bioenergetic processes are under selection in PAH-adapted fish from the most contaminated ER site and ex vivo studies confirmed altered mitochondrial function in these fish. Further analyses extending to differentially PAH-resistant subpopulations showed organismal level bioenergetic shifts in ER fish that are associated with increased cost of living, decreased performance, and altered metabolic response to temperature stress-an indication of reduced thermal plasticity. A movement model predicted a higher energetic cost for PAH-resistant subpopulations when seeking an optimum habitat. Collectively, we demonstrate that pollution adaption and inhabiting contaminated environments may result in physiological shifts leading to compromised organismal capacity to respond to additional stressors.

Growth rate is the most important trait that can be manipulated to create more efficient aquaculture. Crossbreeding, where different populations are bred, has the potential to increase performance through release from inbreeding depression. I crossed a farm population of Chinook salmon (Oncorhynchus tshawytscha) with seven wild populations, then compared growth rate, feed conversion efficiency, swimming speed and metabolic rate between the crossbred and original farmed lines. Crossbreeding resulted in increased growth rates, but had no effect on the other traits. I next evaluated the feasibility of using a diet that replaced fish meal with corn gluten meal and poultry meal. The alternative diet had no effect on growth rate or survival, but led to increased fat content and decreased tissue pigmentation. My thesis supports using crossbreeding in salmon aquaculture to increase growth rate, but found a low fish meal diet was not viable due to its effects on tissue colour.

Several locations in the Elizabeth River, VA, USA are highly contaminated with polycyclic aromatic hydrocarbons (PAHs) due to the release of creosote mixtures from wood treatment facilities. Interestingly, some populations of Atlantic killifish (Fundulus heteroclitus) inhabiting the Elizabeth River (ER) are resistant to PAH-induced teratogenesis. However, evolutionary resistance to PAHs due to chronic PAH exposure is associated with reduced fitness and increased susceptibility to other environmental stressors in at least one PAH-resistant ER killifish population. More specifically, wild-caught and first generation PAH-resistant juvenile killifish have altered metabolic demands when compared to non-resistant fish. Herein, we investigated this association further by examining a previously under-studied population captured from the creosote-contaminated site Republic Creosoting (Rep). We assessed PAH toxicity and effects on energy metabolism in Rep killifish in comparison with killifish from the reference site Kings Creek (KC). Following exposures to simple and complex PAH mixtures, Rep killifish exhibited several phenotypes associated with PAH resistance including decreased incidences of developmental cardiovascular deformities and recalcitrant cytochrome P450 1A (CYP1A) activity. We evaluated bioenergetics in killifish embryos throughout development and found elevated basal oxygen consumption rates in Rep embryos relative to KC embryos. Furthermore, juvenile F1 Rep fish had significantly lower maximal metabolic rates and aerobic scopes than KC juveniles. These results suggest that populations of killifish that have adapted or evolved to withstand the toxicity associated with PAHs consequently have altered energetic metabolism or demands. Such consequences could result in an enhanced vulnerability to other environmental and anthropogenic stressors in PAH-resistant killifish.

Sympatric congeners with similar physiological and morphological characteristics may appear to overlap in niche space but respond to environmental change in different ways leading to population decline of one species while the other remains stable. Understanding why sympatric congeners vary in their ecological success can be challenging, but is particularly necessary given the magnitude of human‐induced environmental change among ecosystems. We propose that identifying a complex of subtle, interacting characters among congeners may be more effective in elucidating both historical coexistence and divergent ecological success in contemporary habitats compared to identifying just one apparent limiting similarity between species. Using this subtle difference hypothesis, we examined how metabolic rate associated with habitat use and internal and external morphology collectively influenced the ecological success of a common and a rare sturgeon species that differ dramatically in their conservation status due to environmental change. Multivariate analyses of gut morphology (e.g., intestine length) combined with respirometry on sand and gravel habitats were incorporated into a bioenergetics model to compare how the fishes responded to habitat change and food quality. Energetic tradeoffs induced by habitat type and underlying morphological differences led to different predicted growth rates. Compared with the more prevalent species, the rare and endangered fish needed to seek different habitats with less energetic costs and switch to foraging at a higher trophic level to persist. Our results corresponded to observed differences in ecological success between these species in the wild. Thus, subtle physiological and morphological differences may lead to dramatic differences in ecological success in contemporary habitats for species that are very similar ecologically.

Conspecifics inhabiting divergent environments frequently differ in morphology, physiology, and performance, but the interrelationships amongst traits and with Darwinian fitness remains poorly understood. We investigated population differentiation in morphology, metabolic rate, and swimming performance in three‐spined sticklebacks ( Gasterosteus aculeatus L.), contrasting a marine/ancestral population with two distinct freshwater morphotypes derived from it: the “typical” low‐plated morph, and a unique “small‐plated” morph. We test the hypothesis that similar to plate loss in other freshwater populations, reduction in lateral plate size also evolved in response to selection. Additionally, we test how morphology, physiology, and performance have evolved in concert as a response to differences in selection between marine and freshwater environments. We raised pure‐bred second‐generation fish originating from three populations and quantified their lateral plate coverage, burst‐ and critical swimming speeds, as well as standard and active metabolic rates. Using a multivariate Q ST ‐ F ST framework, we detected signals of directional selection on metabolic physiology and lateral plate coverage, notably demonstrating that selection is responsible for the reduction in lateral plate coverage in a small‐plated stickleback population. We also uncovered signals of multivariate selection amongst all bivariate trait combinations except the two metrics of swimming performance. Divergence between the freshwater and marine populations exceeded neutral expectation in morphology and in most physiological and performance traits, indicating that adaptation to freshwater habitats has occurred, but through different combinations of traits in different populations. These results highlight both the complex interplay between morphology, physiology and performance in local adaptation, and a framework for their investigation.

A lack of information on the swimming abilities of sauger (Sander canadensis), a highly migratory species particularly sensitive to habitat fragmentation, may inhibit the design of effective passage structures for this species. Passage success, maximum ascent distances, and maximum sprint velocities of sauger were estimated in an open-channel flume over a range of water velocities (51, 78, and 92 cm·s −1 ) and temperatures (10.0, 14.3, and 18.3 °C) to assess swimming performance. Passage success was high (91%) over all test velocities, as was the maximum instantaneous burst velocity (219 cm·s −1 ). Water temperature and body size had little effect on swimming performance. Sauger transitioned from steady, sustained swimming to unsteady, burst–glide, or steady burst swimming at 97 cm·s −1. Sauger were capable of sustained sprints of 124 cm·s −1 over 15 s duration in a swim chamber. Results suggest passage structures with water velocities less than 97 cm·s −1 should provide high probability of successful passage of adult sauger, whereas structures with water velocities exceeding 219 cm·s −1 may be impassable.

We compared oxygen consumption (MO2, mg/kg/h) of c. 80 g rainbow trout (Oncorhynchus mykiss) in an intermittent-flow swim respirometer at 15 °C. Before the tests the fish were grown in flow through tanks (15 °C) with either fishmeal (FM) or corn gluten meal (CGM) based diets (c. 52% protein) for a period of 3–4.5 months. Ten individuals from both treatment groups were fasted for 48 h before the swim test, which consisted of 18 loops of 210 s over three different periods: acclimation period (6 loops at 0.5 body lengths per s, BL/s), exercise period (8 loops at increased speed from 1 to 2.5 BL/s with recovery loops at 0.5 BL/s), and a recovery period (four loops at 0.5 BL/s). We did not observe significant differences in MO2 between the two groups at any of the three measurement periods (repeated measures-Anova). The maximum (mean ± SE) MO2 values, measured during the last exercise period at 2.5 BL/s, did not differ significantly between the treatments: 404 ± 18.7 mg/kg/h and 427 ± 50.6 mg/kg/h in FM and CGM groups, respectively. Our result supports an earlier finding that origin of the protein does not affect MO2 during swimming in salmonids. This is the first report of the effect of a plant protein on MO2 of a carnivorous fish during forced swimming, and these data lend support to further development of sustainable diets to replace fishmeal with plant proteins. Abbreviations: BLbody lengths CFcondition factor CGMcorn gluten meal FMfishmeal MO2oxygen consumption (mg/kg/h)

Diadromy affords fish access to productive ecosystems, increasing growth and ultimately fitness, but it is unclear whether these advantages persist for species migrating within highly altered habitat. Here, we compared the foraging success of wild Delta Smelt—an endangered, zooplanktivorous, annual, semi-anadromous fish that is endemic to the highly altered San Francisco Estuary (SFE)—collected from freshwater (<0.55 psu) and brackish habitat (≥0.55 psu). Stomach fullness, averaged across three generations of wild Delta Smelt sampled from juvenile through adult life stages (n = 1,318), was 1.5-fold higher in brackish than in freshwater habitat. However, salinity and season interacted, with higher fullness (1.7-fold) in freshwater than in brackish habitat in summer, but far higher fullness in brackish than freshwater habitat during fall/winter and winter/spring (1.8 and 2.0-fold, respectively). To examine potential causes of this interaction we compared mesozooplankton abundance, collected concurrently with the Delta Smelt, in freshwater and brackish habitat during summer and fall/winter, and the metabolic rate of sub-adult Delta Smelt acclimated to salinities of 0.4, 2.0, and 12.0 psu in a laboratory experiment. A seasonal peak in mesozooplankton density coincided with the summer peak in Delta Smelt foraging success in freshwater, and a pronounced decline in freshwater mesozooplankton abundance in the fall coincided with declining stomach fullness, which persisted for the remainder of the year (fall, winter and spring). In brackish habitat, greater foraging ‘efficiency’ (prey items in stomachs/mesozooplankton abundance) led to more prey items per fish and generally higher stomach fullness (i.e., a higher proportion of mesozooplankton detected in concurrent trawls were eaten by fish in brackish habitat). Delta Smelt exhibited no difference in metabolic rate across the three salinities, indicating that metabolic responses to salinity are unlikely to have caused the stomach fullness results. Adult migration and freshwater spawning therefore places young fish in a position to exploit higher densities of prey in freshwater in the late spring/summer, and subsequent movement downstream provides older fish more accessible prey in brackish habitat. Thus, despite endemism to a highly-altered estuary, semi-anadromy provided substantial foraging benefits to Delta Smelt, consistent with other temperate migratory fish.

Developmental plasticity of cardiorespiratory physiology in response to chronic hypoxia is poorly understood in larval fishes, especially larval air-breathing fishes, which eventually in their development can at least partially "escape" hypoxia through air breathing. Whether the development air breathing makes these larval fishes less or more developmentally plastic than strictly water breathing larval fishes remains unknown. Consequently, developmental plasticity of cardiorespiratory physiology was determined in two air-breathing anabantid fishes ( Betta splendens and Trichopodus trichopterus ). Larvae of both species experienced an hypoxic exposure that mimicked their natural environmental conditions, namely chronic nocturnal hypoxia (12 h at 17 kPa or 14 kPa), with a daily return to diurnal normoxia. Chronic hypoxic exposures were made from hatching through 35 days postfertilization, and opercular and heart rates measured as development progressed. Opercular and heart rates in normoxia were not affected by chronic nocturnal hypoxic. However, routine oxygen consumption M˙O2 (~4 μ mol·O 2 /g per hour in normoxia in larval Betta ) was significantly elevated by chronic nocturnal hypoxia at 17 kPa but not by more severe (14 kPa) nocturnal hypoxia. Routine M˙O2 in Trichopodus (6-7 μ mol·O 2 /g per hour), significantly higher than in Betta, was unaffected by either level of chronic hypoxia. P Crit, the PO 2 at which M˙O2 decreases as ambient PO 2 falls, was measured at 35 dpf, and decreased with increasing chronic hypoxia in Betta, indicating a large, relatively plastic hypoxic tolerance. However, in contrast, P Crit in Trichopodus increased as rearing conditions grew more hypoxic, suggesting that hypoxic acclimation led to lowered hypoxic resistance. Species-specific differences in larval physiological developmental plasticity thus emerge between the relatively closely related Betta and Trichopodus Hypoxic rearing increased hypoxic tolerance in Betta, which inhabits temporary ponds with nocturnal hypoxia. Trichopodus, inhabiting more permanent oxygenated bodies of water, showed few responses to hypoxia, reflecting a lower degree of developmental phenotypic plasticity.

This study investigated interactions of temperature and hypoxia on metabolic plasticity and regulation in zebrafish, Danio rerio, in the first week of development. Larval morphometry, oxygen consumption, and metabolic responses to acute changes in temperature and oxygen were measured in larvae reared under four conditions, including control (28°C and partial pressures of oxygen [ P O 2 ] of 21 kPa), high temperature (31°C), hypoxia (11 kPa), and the two stressors combined. Rearing conditions did not result in consistent morphometric changes; substantial metabolic adjustments, however, were evident. While acute temperature increase resulted in elevated oxygen consumption, with a Q 10 of 2.2 ± 0.08, early‐staged larvae were able to compensate to chronic temperature rise as routine metabolic rates did not differ between 28°C and 31°C chronic treatments. In contrast, larval responses to chronic and acute hypoxia were similar, with ∼30% decrease in metabolic rates from normoxic values at both temperatures. Further, prior exposure to chronic hypoxia in conjunction with acute high temperature increased Q 10 by a factor of 2.5 from 2.2 ± 0.08 to 5.6 ± 0.19. Metabolic suppression by acute hypoxia was independent of any prior exposure conditions. In short, results from this study showed that zebrafish larvae exhibited surprising temperature resilience and metabolic plasticity to a 3°C temperature rise even in their first week of life. Yet exposure to a second stressor (hypoxia) resulted in elevated sensitivity to temperature change that may lead to bioenergetic imbalance due to synergetic effects of temperature and hypoxia on metabolic rates.

The rate of hypoxia induction (RHI) is an important but overlooked dimension of environmental hypoxia that may affect an organism’s survival. We hypothesized that, compared with rapid RHI, gradual RHI will afford an organism more time to alter plastic phenotypes associated with O2 uptake and subsequently reduce the critical O2 tension (Pcrit) of O2 uptake rate (ṀO2). We investigated this by determining Pcrit values for goldfish exposed to short (∼24 min), typical (∼84 min) and long (∼480 min) duration Pcrit trials to represent different RHIs. Consistent with our predictions, long duration Pcrit trials yielded significantly lower Pcrit values (1.0-1.4 kPa) than short and typical duration trials, which did not differ (2.6±0.3 and 2.5±0.2 kPa, respectively). Parallel experiments revealed these time-related shifts in Pcrit were associated with changes in aspects of the O2 transport cascade: gill surface areas and haemoglobin-O2 binding affinities were significantly higher in fish exposed to gradual RHIs over 480 min than fish exposed to rapid RHIs over 60 min. Our results also revealed that the choice of respirometric technique (i.e., closed versus intermittent) does not affect Pcrit or routine ṀO2, despite the significantly reduced water pH and elevated CO2 and ammonia levels measured following closed-circuit Pcrit trials of ∼90 min. Together, our results demonstrate that gradual RHIs result in alterations to physiological parameters that enhance O2 uptake in hypoxic environments. An organism’s innate Pcrit is therefore most accurately determined using rapid RHIs (<90 min) so as to avoid the confounding effects of hypoxic acclimation.

Although the mitochondrial metabolism responses to warm acclimation have been widely studied in fish, the time course of this process is less understood. Here, we characterise changes of rainbow trout (Oncorhyncus mykiss) cardiac mitochondrial metabolism during acute warming from 10 to 16°C, and during the subsequent warm acclimation for 39 days (D). We repeatedly measured mitochondrial O2 consumption in cardiac permeabilized fibers and functional integrity of mitochondria (i.e. mitochondrial coupling and cytochrome c effect) at two assay temperatures (10 and 16°C), as well as citrate synthase (CS) and lactate dehydrogenase (LDH) activities at room temperature. LDH and CS activities significantly increased between D0 (10°C acclimated fish) and D1 (acute warming to 16°C), while mitochondrial O2 consumption measured at respective in vivo temperatures did not change. Enzymatic activities and mitochondrial O2 consumption rates significantly decreased by D2, and remained stable during warm acclimation (D2-39). The decrease in rates of O2 between D0 and D1 coincided with an increased cytochrome c effect and a decreased mitochondrial coupling, suggesting a structural/functional impairment of mitochondria during acute warming. We suggest that after two days of warm acclimation, a new homeostasis is reached, which may involve removal of dysfunctional mitochondria. Interestingly, from D2 onward, there was a lack of differences in mitochondrial O2 consumption rates between the assay temperatures, suggesting that warm acclimation reduces the acute thermal sensitivity of mitochondria. This study provides significant knowledge on the thermal sensitivity of cardiac mitochondria that is essential to delineate the contribution of cellular processes to warm acclimation.

Nanosilver (nAg) has been incorporated into many consumer products, including clothing and washing machines, because of its antimicrobial properties. Consequently, the potential for its release into aquatic environments is of significant concern. Documented toxic effects on fish include altered gene expression, gill damage, and impaired gas exchange, as well as mortality at high nAg concentrations. The present study reports the effects of nAg on the metabolism of rainbow trout (Oncorhynchus mykiss). Fish were exposed to environmentally relevant concentrations (0.28 ± 0.02 μg/L) and higher (47.60 ± 5.13 μg/L) for 28 d, after which their standard metabolic rate (SMR), forced maximum metabolic rate (MMRf), and spontaneous maximum metabolic rate (MMRs) were measured. There was no effect observed in SMR, MMRf, or MMRs, suggesting that nAg is unlikely to directly affect fish metabolism. On average, MMRs tended to be greater than MMRf, and most MMRs occurred when room lighting increased. The timing of MMRf chase protocols was found to affect both MMRf and SMR estimates, in that chasing fish before respirometric experiments caused higher MMRf estimates and lower SMR estimates. Although compounded effects involving nAg and other environmental stressors remain unknown, the present study indicates that the tested range of nAg is unlikely to constrain fish metabolism. Environ Toxicol Chem 2017;36:2722–2729. © 2017 SETAC

Municipal wastewater effluent is a major source of aquatic pollution and has potential to impact cellular energy metabolism. However, it is poorly understood whether wastewater exposure impacts whole-animal metabolism and whether this can be accommodated with adjustments in respiratory physiology. We caged bluegill sunfish (Lepomis macrochirus) for 21 days at two sites downstream (either 50 or 830 m) from a wastewater treatment plant (WWTP). Survival was reduced in fish caged at both downstream sites compared to an uncontaminated reference site. Standard rates of O 2 consumption increased in fish at contaminated sites, reflecting a metabolic cost of wastewater exposure. Several physiological adjustments accompanied this metabolic cost, including an expansion of the gill surface area available for gas exchange (reduced interlamellar cell mass), a decreased blood-O 2 affinity (which likely facilitates O 2 unloading at respiring tissues), increased respiratory capacities for oxidative phosphorylation in isolated liver mitochondria (supported by increased succinate dehydrogenase, but not citrate synthase, activity), and decreased mitochondrial emission of reactive oxygen species (ROS). We conclude that exposure to wastewater effluent invokes a metabolic cost that leads to compensatory respiratory improvements in O 2 uptake, delivery, and utilization.

Fertilization and development in salmonids occurs almost exclusively within freshwater environments (< 1 ppt). A less common life history strategy in this group of fishes is the brackish-water resident life history, where entire life cycles occur in brackish water (> 1 ppt). In the present study, we tested the hypothesis that differences in rearing environment (fresh or brackish water) results in significant differences in the ability of lake trout to ionoregulate when faced with a salinity challenge later in life. To test this, genetically similar lake trout were fertilized and raised at either 0 or 5 ppt saltwater. At approximately 240 days post hatch, lake trout from both rearing environments were acutely transferred to 20 ppt salt water or their respective rearing environments as a control. Individuals were sampled at time 0, 1, 7, and 14 days post transfer. Fish raised in 5 ppt transferred to 20 ppt saltwater had significantly higher gill Na+ K+-ATPase activity, gill Na+ K+-ATPase α1b expression, and lower plasma osmolality when compared to freshwater reared lake trout transferred to 20 ppt across various time points. Additionally, the 5 ppt control treatment had greater overall aerobic scope than 0 ppt control fish and those transferred from 0 ppt to 20 ppt. These data imply that populations exhibiting a brackish-water resident life history, as has been observed in Arctic Canada, may have an advantage over freshwater reared conspecifics when foraging in marine influenced environments and colonizing new locations in coastal regions.

Deciphering the mechanisms by which climate change interacts with invasive species to affect biodiversity is a major challenge of global change biology. We conducted experiments to determine whether the global invader, Gambusia holbrooki, was more resistant to high water temperature (heat) and low dissolved oxygen (hypoxia) than a threatened native fish, Nannoperca australis. Metabolic experiments conducted at 25 and 29 °C showed that G. holbrooki had at least four times the capacity for metabolic depression during hypoxia than N. australis. An increase in environmental temperature from 25 to 29 °C had no significant impact on the critical oxygen tension, P crit, of G. holbrooki, but significantly and strongly increased P crit of N. australis. Gambusia holbrooki also had a lower Q 10 of standard metabolic rate than N. australis. Our results indicate that G. holbrooki have physiological traits conferring greater resistance to hypoxia than N. australis, and as temperature increases, the resistance of N. australis to hypoxia was more eroded than that of G. holbrooki. Intensive monitoring of the temperature and dissolved oxygen dynamics of wetlands showed that contemporary heat waves are already causing conditions that might give G. holbrooki the edge over N. australis on Australian floodplains. Our study adds weight to recent anecdotal reports of drought and heat waves causing localised extinction of N. australis, but the proliferation of G. holbrooki.

The average global temperature is predicted to increase by 3 °C by the end of this century due to human-induced climate change. The overall metabolism of the aquatic biota will be directly affected by rising temperatures and associated changes. Since thermal stability is a characteristic of groundwater ecosystems, global warming is expected to have a profound effect on the groundwater fauna. The prediction that stygobitic (obligate groundwater dweller) species are vulnerable to climate change includes assumptions about metabolic effects that can only be tested by comparisons across a thermal gradient. To this end, we investigated the effects of two different thermal regimes on the metabolism of the stygobitic copepod species Diacyclops belgicus (Kiefer, 1936). We measured the individual-based oxygen consumption of this species as a proxy of possible metabolic reactions to temperature rising from 14 to 17 °C. We used a sealed glass microplate equipped with planar oxygen sensor spots with optical isolation glued onto the bottom of 80-μL wells integrated with a 24-channel fluorescence-based respirometry system. The tests have provided controversial results according to which the D. belgicus populations should be prudently considered at risk under a global warming scenario.

Environmental change may cause phenotypic changes that are inherited across generations through transgenerational plasticity (TGP). If TGP is adaptive, offspring fitness increases with an increasing match between parent and offspring environment. Here we test for adaptive TGP in somatic growth and metabolic rate in response to temperature in the clonal zooplankton Daphnia pulex. Animals of the first focal generation experienced thermal transgenerational ‘mismatch’ (parental and offspring temperatures differed), whereas conditions of the next two generations matched the (grand)maternal thermal conditions. Adjustments of metabolic rate occurred during the lifetime of the first generation (i.e. within-generation plasticity). However, no further change was observed during the subsequent two generations, as would be expected under TGP. Furthermore, we observed no tendency for increased juvenile somatic growth (a trait highly correlated with fitness in Daphnia ) over the three generations when reared at new temperatures. These results are inconsistent with existing studies of thermal TGP, and we describe how previous experimental designs may have confounded TGP with within-generation plasticity and selective mortality. We suggest that the current evidence for thermal TGP is weak. To increase our understanding of the ecological and evolutionary role of TGP, future studies should more carefully identify possible confounding factors.

For ectotherms, temperature modifies the rate of physiological function across a temperature tolerance window depending on thermal history, ontogeny, and evolutionary history. Some adult Antarctic fishes, with comparatively narrow thermal windows, exhibit thermal plasticity in standard metabolic rate; however, little is known about the shape or breadth of thermal performance curves of earlier life stages of Antarctic fishes. We tested the effects of acute warming (− 1 to 8 °C) and temperature acclimation (2 weeks at − 1, 2, 4 °C) on survival and standard metabolic rate in early embryos of the dragonfish Gymnodraco acuticeps from McMurdo Sound, Ross Island, Antarctica. Contrary to predictions, embryos acclimated to warmer temperatures did not experience greater mortality and nearly all embryos survived acute warming to 8 °C. Metabolic performance curve height and shape were both significantly altered after 2 weeks of development at − 1 °C, with further increase in curve height, but not alteration of shape, with warm temperature acclimation. Overall metabolic rate temperature sensitivity (Q 10) from − 1 to 8 °C varied from 2.6 to 3.6, with the greatest thermal sensitivity exhibited by embryos at earlier developmental stages. Interclutch variation in metabolic rates, mass, and development of simultaneously collected embryos was also documented. Taken together, metabolic performance curves provide insight into the costs of early development under warming temperatures, with the potential for thermal sensitivity to be modified by dragonfish phenology and magnitude of seasonal changes in temperature.

Within many species, larger offspring have higher fitness. While the presence of an offspring size–fitness relationship is canonical in life‐history theory, the mechanisms that determine why this relationship exists are unclear. Linking metabolic theory to life‐history theory could provide a general explanation for why larger offspring often perform better than smaller offspring. In many species, energy reserves at the completion of development drive differences in offspring fitness. Development is costly, so any factor that decreases energy expenditure during development should result in higher energy reserves and thus subsequently offspring fitness. Metabolic theory predicts that larger offspring should have relatively lower metabolic rates and thus emerge with a higher level of energy reserves (assuming developmental times are constant). The increased efficiency of development in larger offspring may therefore be an underlying driver of the relationship between offspring size and offspring fitness, but this has not been tested within species. To determine how the costs of development scale with offspring size, we measured energy expenditure throughout development in the model organism Danio rerio across a range of natural offspring sizes. We also measured how offspring size affects the length of the developmental period. We then examined how hatchling size and condition scale with offspring size. We find that larger offspring have lower mass‐specific metabolic rates during development, but develop at the same rate as smaller offspring. Larger offspring also hatch relatively heavier and in better condition than smaller offspring. That the relative costs of development decrease with offspring size may provide a widely applicable explanation for why larger offspring often perform better than smaller offspring. A plain language summary is available for this article.

The effects of multiple stressors on the early life stages of reef-building corals are poorly understood. Elevated temperature is the main physiological driver of mass coral bleaching events, but increasing evidence suggests that other stressors, including elevated dissolved inorganic nitrogen (DIN), may exacerbate the negative effects of thermal stress. To test this hypothesis, we investigated the performance of larvae of Orbicella faveolata and Porites astreoides, two important Caribbean reef coral species with contrasting reproductive and algal transmission modes, under increased temperature and/or elevated DIN. We used a fluorescence-based microplate respirometer to measure the oxygen consumption of coral larvae from both species, and also assessed the effects of these stressors on P. astreoides larval settlement and mortality. Overall, we found that (1) larvae increased their respiration in response to different factors (O. faveolata in response to elevated temperature and P. astreoides in response to elevated nitrate) and (2) P. astreoides larvae showed a significant increase in settlement as a result of elevated nitrate, but higher mortality under elevated temperature. This study shows how microplate respirometry can be successfully used to assess changes in respiration of coral larvae, and our findings suggest that the effects of thermal stress and nitrate enrichment in coral larvae may be species specific and are neither additive nor synergistic for O. faveolata or P. astreoides. These findings may have important consequences for the recruitment and community reassembly of corals to nutrient-polluted reefs that have been impacted by climate change.

Energetic costs associated with ion and acid-base regulation in response to ocean acidification have been predicted to decrease the energy available to fish for basic life processes. However, the low cost of ion regulation (6–15% of standard metabolic rate) and inherent variation associated with whole-animal metabolic rate measurements have made it difficult to consistently demonstrate such a cost. Here we aimed to gain resolution in assessing the energetic demand associated with acid-base regulation by examining ion movement and O 2 consumption rates of isolated intestinal tissue from Gulf toadfish acclimated to control or 1900 μatm CO 2 (projected for year 2300). The active marine fish intestine absorbs ions from ingested seawater in exchange for HCO 3 − to maintain water balance. We demonstrate that CO 2 exposure causes a 13% increase of intestinal HCO 3 − secretion that the animal does not appear to regulate. Isolated tissue from CO 2 -exposed toadfish also exhibited an 8% higher O 2 consumption rate than tissue from controls. These findings show that compensation for CO 2 leads to a seemingly maladaptive persistent base (HCO 3 − ) loss that incurs an energetic expense at the tissue level. Sustained increases to baseline metabolic rate could lead to energetic reallocations away from other life processes at the whole-animal level.

Climate change and associated increases in water temperatures may impact physiological performance in ectotherms and exacerbate endangered species declines. We used an integrative approach to assess the impact of elevated water temperature on two fishes of immediate conservation concern in a large estuary system, the threatened longfin smelt (Spirinchus thaleichthys) and endangered delta smelt (Hypomesus transpacificus). Abundances have reached record lows in California, USA, and these populations are at imminent risk of extirpation. California is currently impacted by a severe drought, resulting in high water temperatures, conditions that will become more common as a result of climate change. We exposed fish to environmentally relevant temperatures (14°C and 20°C) and used RNA sequencing to examine the transcriptome-wide responses to elevated water temperature in both species. Consistent with having a lower temperature tolerance, longfin smelt exhibited a pronounced cellular stress response, with an upregulation of heat shock proteins, after exposure to 20°C that was not observed in delta smelt. We detected an increase in metabolic rate in delta smelt at 20°C and increased expression of genes involved in metabolic processes and protein synthesis, patterns not observed in longfin smelt. Through examination of responses across multiple levels of biological organization, and by linking these responses to habitat distributions in the wild, we demonstrate that longfin smelt may be more susceptible than delta smelt to increases in temperatures, and they have little room to tolerate future warming in California. Understanding the species-specific physiological responses of sensitive species to environmental stressors is crucial for conservation efforts and managing aquatic systems globally.

Hyperventilation is a common response in fish exposed to elevated water CO2. It is believed to lessen the respiratory acidosis associated with hypercapnia by lowering arterial PCO2, but the contribution of hyperventilation to blood acid–base compensation has yet to be quantified. Hyperventilation may also increase the flux of irons across the gill epithelium and the cost of osmoregulation, owing to the osmo-respiratory compromise. Therefore, hypercapnia exposed fish may increase standard metabolic rate (SMR) leaving less energy for physiological functions such as foraging, migration, growth and reproduction. Here we show that gill ventilation, blood PCO2 and total blood [CO2] increased in red drum (Sciaenops ocellatus) exposed to 1000 and 5000 µatm water CO2, and that blood PCO2 and total blood [CO2] decrease in fish during hypoxia induced hyperventilation. Based on these results we estimate the ventilatory contributions to total acid–base compensation in 1000 and 5000 µatm water CO2. We find that S. ocellatus only utilize a portion of its ventilatory capacity to reduce the acid–base disturbance in 1000 µatm water CO2. SMR was unaffected by both salinity and hypercapnia exposure indicating that the cost of osmoregulation is small relative to SMR, and that the lack of increased ventilation in 1000 µatm water CO2 despite the capacity to do so is not due to an energetic tradeoff between acid–base balance and osmoregulation. Therefore, while ocean acidification may impact ventilatory parameters, there will be little impact on the overall energy budget of S. ocellatus.

Effects of dietary seaweed supplementation on basal physiology and health biomarkers were assessed in meagre (Argyrosomus regius) subjected to bacterial infection, using Photobacterium damselae subsp. Piscicida (Phdp) as the etiologic agent. Three test diets were prepared by supplementing a basal control formulation (44 % protein, 16 % lipid, 22 kJ g−1 energy) with 0 % seaweed (control), 5 % Gracilaria sp. or 5 % Alaria sp. During the growth trial, 180 fish (39.70 ± 0.33 g) were daily fed for 69 days with the experimental diets. After the growth trial, 60 fish from each dietary treatment were divided into two groups, infected and non-infected. The infected group was injected intraperitoneally with a saline solution (HBSS) with 2.91 x 103 CFU Phdp g−1 fish, whereas the non-infected group was injected with HBSS without Phdp. Dietary seaweed supplementation did not affect fish growth performance. Standard and routine metabolic rates, and aerobic metabolic scope did not vary significantly among dietary treatments. Conversely, maximum metabolic rate was significantly higher in fish fed Alaria sp. diet when compared to control group. Non-infected fish had higher hematocrit levels than the infected group, regardless of diet. Lactate levels were significantly higher in fish fed Alaria sp. diet when compared to control, with no interaction between diet and infection. Lipid peroxidation was significantly higher in fish fed control diet than supplemented diets. Infected groups had lower antioxidant enzymes activities when compared to non-infected. An interaction between infection and diet was found for glutathione peroxidase and reduced glutathione activities. The current study suggests that dietary seaweed supplementation modulates metabolic rates and biomarker responses in meagre, which may confer advantages in coping with biotic stressors.

Survival depends on appropriate behavioural and physiological responses to danger. In addition to active ‘fight‐flight’ defence responses, a passive ‘freeze‐hide’ response is adaptive in some contexts. However, the physiological mechanisms determining which individuals choose a given defence response remain poorly understood. We examined the relationships among personality, metabolic performance and physiological stress responses across an environmental gradient in the olive flounder, Paralichthys olivaceus. We employed four behavioural assays to document the existence of two distinct behavioural types (‘bold’ and ‘shy’) in this species. We found consistent metabolic differences between individuals of a given behavioural type across an environmental gradient: shy individuals had overall lower aerobic scope, maximum metabolic rate and standard metabolic rate than bold individuals in both high (25 ppt) and low (3 ppt) salinity. These behavioural and metabolic differences translated into divergent physiological responses during acute stress: shy individuals adopted a passive ‘freeze‐hide’ response by reducing their oxygen consumption rates (akin to shallow breathing) whereas bold individuals adopted an active ‘fight‐flight’ response by increasing their rates of respiration. These distinct defence strategies were repeatable within individuals between salinity treatments. Although it has been suggested theoretically, this is the first empirical evidence that the metabolic response to stressful situations differs between bold and shy individuals. Our results emphasize the importance of incorporating physiological measures to understand the mechanisms driving persistent inter‐individual differences in animals.

Differences in aggressiveness when competing for environmental resources are the main factor leading to social hierarchy in group living fish. Social status acquired is related to changes in physiological parameters, as metabolic rate. Habitat variation can interfere with aggressive behaviour and promote changes in physiological parameters associated with social status. The primary goal of our study was to investigate how differences in habitat complexity affect the relationship between resting metabolic rate (RMR) and social status in the Amazonian dwarf cichlid Apistogramma agassizii. We compared agonistic interactions between pairs of males in aquaria with different habitat enrichment levels, manipulated by adding shelters. RMR was measured before and after hierarchy establishment. Habitat enrichment promotes changes in aggressive behaviour and influences differences in metabolic rate between dominant and subordinate fish. We observed an increase in biting by dominant fish at high enrichment habitat, which could be related to the increase in territory value. We observed an increase in metabolic rate in dominant fish after hierarchy establishment. However, it occurs only in enriched habitats. We concluded that habitat structure interfere with behavioural characteristics in social hierarchies, as aggressiveness, and changes in aggressive interactions affect metabolic rate in different social ranks in the dwarf cichlid Apistogramma agassizii.

Ongoing climate change is predicted to affect the distribution and abundance of aquatic ectotherms owing to increasing constraints on organismal physiology, in particular involving the metabolic scope (MS) available for performance and fitness. The oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis prescribes MS as an overarching benchmark for fitness-related performance and assumes that any anaerobic contribution within the MS is insignificant. The MS is typically derived from respirometry by subtracting standard metabolic rate from the maximal metabolic rate; however, the methodology rarely accounts for anaerobic metabolism within the MS. Using gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata), this study tested for trade-offs (i) between aerobic and anaerobic components of locomotor performance; and (ii) between the corresponding components of the MS. Data collection involved measuring oxygen consumption rate at increasing swimming speeds, using the gait transition from steady to unsteady (burst-assisted) swimming to detect the onset of anaerobic metabolism. Results provided evidence of the locomotor performance trade-off, but only in S. aurata. In contrast, both species revealed significant negative correlations between aerobic and anaerobic components of the MS, indicating a trade-off where both components of the MS cannot be optimized simultaneously. Importantly, the fraction of the MS influenced by anaerobic metabolism was on average 24.3 and 26.1% in S. aurata and P. reticulata, respectively. These data highlight the importance of taking anaerobic metabolism into account when assessing effects of environmental variation on the MS, because the fraction where anaerobic metabolism occurs is a poor indicator of sustainable aerobic performance. Our results suggest that without accounting for anaerobic metabolism within the MS, studies involving the OCLTT hypothesis could overestimate the metabolic scope available for sustainable activities and the ability of individuals and species to cope with climate change.

The temporal and geographic attributes of the Deepwater Horizon incident in 2010 likely exposed pelagic game fish species, such as mahi-mahi, to crude oil. Although much of the research assessing the effects of the spill has focused on early life stages of fish, studies examining whole-animal physiological responses of adult marine fish species are lacking. Using swim chamber respirometry, the present study demonstrates that acute exposure to a sublethal concentration of the water accommodated fraction of Deepwater Horizon crude oil results in significant swim performance impacts on young adult mahi-mahi, representing the first report of acute sublethal toxicity on adult pelagic fish in the Gulf of Mexico following the spill. At an exposure concentration of 8.4 ± 0.6 µg L−1 sum of 50 selected polycyclic aromatic hydrocarbons (PAHs; mean of geometric means ± standard error of the mean), significant decreases in the critical and optimal swimming speeds of 14% and 10%, respectively (p < 0.05), were observed. In addition, a 20% reduction in the maximum metabolic rate and a 29% reduction in aerobic scope resulted from exposure to this level of ΣPAHs. Using environmentally relevant crude oil exposure concentrations and a commercially and ecologically valuable Gulf of Mexico fish species, the present results provide insight into the effects of the Deepwater Horizon oil spill on adult pelagic fish. Environ Toxicol Chem 2016;35:2613–2622. © 2016 SETAC

We designed two environmentally relevant thermal cycling regimes using monitoring data from an Atlantic salmon (Salmo salar) river to determine whether exposure to prior diel cycles stimulated protective mechanisms (e.g., heat hardening) and (or) resulted in physiological and cellular stress. Wild fish were exposed to 3 days of diel cycling in the lab and then exposed to an acute thermal challenge near their upper reported critical temperature. We measured routine metabolic rate across the time course as well as indicators of physiological status (e.g., plasma glucose and osmolality) and cellular stress (e.g., heat shock protein 70). We observed that thermal cycling altered physiological and cellular responses, compared with an acute heat shock, but saw no differences between cycling regimes. Unique temperature regime and tissue-specific responses were observed in heat shock protein induction, metabolites, haematology, and osmotic indicators. Routine metabolic rate was not affected by the thermal cycling and increased according to Q 10 predictions. While we report unique physiological and cellular responses among all treatment groups, we did not observe a clear indication of a heat hardening response.

This study aims to evaluate the effects of adding salt to water on the physiological parameters of the blood parrot cichlid (Cichlasoma synspilum ♀ × Cichlasoma citrinellum ♂). The blood parrot cichlid is a popular species in the aquarium trade because of its behaviour and beauty. Salt is usually added to water during the culture or transportation of this fish. However, the manner by which the fish adjusts its physiological responses to salinity change is unclear. The effects of salinity on serum osmolality, immune-related enzyme activities, Na+–K+-ATPase activities in the gill, skin carotenoid content and oxygen consumption were analysed. Blood parrotfish individuals were transferred from freshwater to water with four salinity levels (0.16, 2.5, 5 and 7.5 ‰) for 168 h, and physiological responses were evaluated at 0, 6, 12, 24 and 168 h. Results showed no significant differences in serum acid phosphatase and alkaline phosphatase activities, skin carotenoid content and oxygen consumption rate among the different groups. However, the serum osmolality at 6 h was significantly elevated. Moreover, salinity increase stimulated superoxide dismutase (SOD) activity from 0 to 6 h. SOD activity increased from 6 to 24 h but significantly reduced at 168 h when the fish were exposed to salt water. The SOD activity in the salinity 2.5 ‰ group recovered the initial level, whereas those in the salinity 5 and 7.5 ‰ groups decreased to levels lower than the initial level. The gill Na+–K+-ATPase activity significantly declined with time and salinity increase. Thus, adding an appropriate amount of salt can save energy consumption during osmoregulation and temporarily enhance the antioxidant activity of blood parrotfish. However, this strategy is insufficient for long-term culture. Therefore, adding salt to water only provides short-term benefit to blood parrot cichlid during transportation.

Specific dynamic action ( SDA ) is the postprandial increase in oxygen uptake. Whereas it is easy to measure in fishes that remain calm and motionless during the entire digestion period, spontaneous locomotor activity is a frequent problem that leads to overestimation of SDA amplitude and magnitude (area under the curve, bound by the standard metabolic rate, SMR ). Few studies have attempted to remove the effect of fish activity on SDA. A new method, non‐parametric quantile regression, is described to estimate SDA even when pronounced circadian activity cycles are present. Data from juvenile Atlantic cod Gadus morhua are used to demonstrate its use and advantages compared with traditional techniques. Software (scripts in the R language) is provided to facilitate its use.

This review and data analysis outline how fish biologists should most reliably estimate the minimal amount of oxygen needed by a fish to support its aerobic metabolic rate (termed standard metabolic rate; SMR ). By reviewing key literature, it explains the theory, terminology and challenges underlying SMR measurements in fishes, which are almost always made using respirometry (which measures oxygen uptake, Ṁ O 2 ). Then, the practical difficulties of measuring SMR when activity of the fish is not quantitatively evaluated are comprehensively explored using 85 examples of Ṁ O 2 data from different fishes and one crustacean, an analysis that goes well beyond any previous attempt. The main objective was to compare eight methods to estimate SMR. The methods were: average of the lowest 10 values (low10) and average of the 10% lowest Ṁ O 2 values, after removing the five lowest ones as outliers (low10%), mean of the lowest normal distribution ( MLND ) and quantiles that assign from 10 to 30% of the data below SMR ( q 0·1, q 0·15, q 0·2, q 0·25 and q 0·3 ). The eight methods yielded significantly different SMR estimates, as expected. While the differences were small when the variability was low amongst the Ṁ O 2 values, they were important (>20%) for several cases. The degree of agreement between the methods was related to the c.v. of the observations that were classified into the lowest normal distribution, the c.v. MLND ( C.V. MLND ). When this indicator was low (≤5·4), it was advantageous to use the MLND, otherwise, one of the q 0·2 or q 0·25 should be used. The second objective was to assess if the data recorded during the initial recovery period in the respirometer should be included or excluded, and the recommendation is to exclude them. The final objective was to determine the minimal duration of experiments aiming to estimate SMR. The results show that 12 h is insufficient but 24 h is adequate. A list of basic recommendations for practitioners who use respirometry to measure SMR in fishes is provided.

The present study determined the blood plasma osmolality and oxygen consumption of the perch Perca fluviatilis at different salinities (0, 10 and 15) and temperatures (5, 10 and 20° C). Blood plasma osmolality increased with salinity at all temperatures. Standard metabolic rate ( SMR ) increased with salinity at 10 and 20° C. Maximum metabolic rate ( MMR ) and aerobic scope was lowest at salinity of 15 at 5° C, yet at 20° C, they were lowest at a salinity of 0. A cost of osmoregulation ( SMR at a salinity of 0 and 15 compared with SMR at a salinity of 10) could only be detected at a salinity of 15 at 20° C, where it was 28%. The results show that P. fluviatilis have capacity to osmoregulate in hyper‐osmotic environments. This contradicts previous studies and indicates intraspecific variability in osmoregulatory capabilities among P. fluviatilis populations or habitat origins. An apparent cost of osmoregulation (28%) at a salinity of 15 at 20° C indicates that the cost of osmoregulation in P. fluviatilis increases with temperature under hyperosmotic conditions and a power analysis showed that the cost of osmoregulation could be lower than 12·5% under other environmental conditions. The effect of salinity on MMR is possibly due to a reduction in gill permeability, initiated to reduce osmotic stress. An interaction between salinity and temperature on aerobic scope shows that high salinity habitats are energetically beneficial during warm periods (summer), whereas low salinity habitats are energetically beneficial during cold periods (winter). It is suggested, therefore, that the seasonal migrations of P. fluviatilis between brackish and fresh water is to select an environment that is optimal for metabolism and aerobic scope.

Metabolic rate is one of the most widely measured physiological traits in animals and may be influenced by both endogenous ( e.g. body mass) and exogenous factors ( e.g. oxygen availability and temperature). Standard metabolic rate ( SMR ) and maximum metabolic rate ( MMR ) are two fundamental physiological variables providing the floor and ceiling in aerobic energy metabolism. The total amount of energy available between these two variables constitutes the aerobic metabolic scope ( AMS ). A laboratory exercise aimed at an undergraduate level physiology class, which details the appropriate data acquisition methods and calculations to measure oxygen consumption rates in rainbow trout Oncorhynchus mykiss, is presented here. Specifically, the teaching exercise employs intermittent flow respirometry to measure SMR and MMR, derives AMS from the measurements and demonstrates how AMS is affected by environmental oxygen. Students' results typically reveal a decline in AMS in response to environmental hypoxia. The same techniques can be applied to investigate the influence of other key factors on metabolic rate ( e.g. temperature and body mass). Discussion of the results develops students' understanding of the mechanisms underlying these fundamental physiological traits and the influence of exogenous factors. More generally, the teaching exercise outlines essential laboratory concepts in addition to metabolic rate calculations, data acquisition and unit conversions that enhance competency in quantitative analysis and reasoning. Finally, the described procedures are generally applicable to other fish species or aquatic breathers such as crustaceans ( e.g. crayfish) and provide an alternative to using higher (or more derived) animals to investigate questions related to metabolic physiology.

Mass‐specific oxygen consumption rate, i.e. standard metabolic rate ( R s ) and critical oxygen tension ( P crit ) of red drum Sciaenops ocellatus were measured and scaled over a 2500‐fold range in mass ( M F; 0·26–686 g). R s conformed to well established models ( R s = 3·73·91 M F −0·21; r 2 = 0·86) while P crit increased over the size range ( P crit = 3·15 log 10 M F + 16·19; r 2 = 0·44). This relationship may be ecologically advantageous as it would allow smaller S. ocellatus to better utilize hypoxic zones as habitat and refuge from predators.

This study tested for links among behaviour, state and life‐history variables as predicted by the pace‐of‐life hypothesis in adult pike Esox lucius. First, a standardized open‐field behavioural assay was developed to assess individual behaviour of wild‐captured adult E. lucius. Behaviour within the standardized assay predicted swimming behaviour in the lake, providing an ecological validation of the assay. There was no relationship between standardized behaviour and any of the life‐history and state variables, including metabolism, body condition, juvenile growth rate and adult growth rate in contrast to predictions from the pace‐of‐life hypothesis. This study demonstrates that it is possible to assess ecologically relevant behavioural variation in a large‐bodied top predator using a standard open‐field assay, but it is noteworthy that this standardized behaviour is not systematically related to standard metabolism or growth.

To maximize reproductive success, many animal species have evolved functional sex change. Theory predicts that transitions between sexes should occur when the fitness payoff of the current sex is exceeded by the fitness payoff of the opposite sex. We examined phenotypic differences between the sexes in a sex-changing vertebrate, the mangrove rivulus fish (Kryptolebias marmoratus), to elucidate potential factors that might drive the ‘decision’ to switch sex. Rivulus populations consist of self-fertilizing hermaphrodites and males. Hermaphrodites transition into males under certain environmental conditions, affording us the opportunity to generate 40 hermaphrodite–male pairs where, within a pair, individuals possessed identical genotypes despite being different sexes. We quantified steroid hormone levels, behavior (aggression and risk taking), metabolism and morphology (organ masses). We found that hermaphrodites were more aggressive and risk averse, and had higher maximum metabolic rates and larger gonadosomatic indices. Males had higher steroid hormone levels and showed correlations among hormones that hermaphrodites lacked. Males also had greater total mass and somatic body mass and possessed considerable fat stores. Our findings suggest that there are major differences between the sexes in energy allocation, with hermaphrodites exhibiting elevated maximum metabolic rates, and showing evidence of favoring investments in reproductive tissues over somatic growth. Our study serves as the foundation for future research investigating how environmental challenges affect both physiology and reproductive investment and, ultimately, how these changes dictate the transition between sexes.

The changes in ocean chemistry stemming from anthropogenic CO2 release—termed ocean acidification (OA)—are predicted to have wide-ranging effects on fish and ultimately threaten global populations. The ability of fish to adapt to environmental change is currently unknown, but phenotypic plasticity has been highlighted as a crucial factor in determining species resilience. Here we show that red drum, a long-lived estuarine-dependent fish species native to the Gulf of Mexico, exhibit respiratory plasticity that increases CO2 excretion capacity when acclimated to OA conditions. Specifically, fish exposed to 14 days of 1000 µatm CO2 had a 32 % reduction in branchial diffusion distance and increased expression of two putative CO2 channel proteins—rhag and rhcg1. No changes were observed in the erythrocyte CO2 transport pathways. Surprisingly, no significant changes in blood chemistry were observed between acclimated and acutely challenged animals; however, a non-significant 30 % drop in the magnitude of plasma $$C_{{{\text{CO}}_{ 2} }}$$ elevation was observed. Reduced diffusion distance also comes with the cost of increased diffusive water loss, which would require greater osmoregulatory investment by the animal. OA exposure induced increased gill Na+, K+ ATPase activity and intestinal nkcc2 expression, supporting both the presumed osmotic stress and increased osmoregulatory investment. However, no differences in standard metabolic rate, maximum metabolic rate or aerobic scope were detected between control and OA acclimated individuals. Similarly, no differences in critical swim speed were detected between groups, suggesting the energetic cost related to respiratory plasticity is negligible against background metabolism. The current study demonstrated that red drum exhibit respiratory plasticity with only mild physiological trade-offs; however, this plasticity is insufficient to fully offset the OA-induced acid–base disturbance and as such is unlikely to impact species resilience.

The effects of regional variations in oxygen and temperature levels with depth were assessed for the metabolism and hypoxia tolerance of dominant euphausiid species. The physiological strategies employed by these species facilitate prediction of changing vertical distributions with expanding oxygen minimum zones and inform estimates of the contribution of vertically migrating species to biogeochemical cycles. The migrating species from the Eastern Tropical Pacific (ETP), Euphausia eximia and Nematoscelis gracilis, tolerate a Partial Pressure (PO2) of 0.8 kPa at 10 °C (∼15 µM O2) for at least 12 h without mortality, while the California Current species, Nematoscelis difficilis, is incapable of surviving even 2.4 kPa PO2 (∼32 µM O2) for more than 3 h at that temperature. Euphausia diomedeae from the Red Sea migrates into an intermediate oxygen minimum zone, but one in which the temperature at depth remains near 22 °C. Euphausia diomedeae survived 1.6 kPa PO2 (∼22 µM O2) at 22 °C for the duration of six hour respiration experiments. Critical oxygen partial pressures were estimated for each species, and, for E. eximia, measured via oxygen consumption (2.1 kPa, 10 °C, n = 2) and lactate accumulation (1.1 kPa, 10 °C). A primary mechanism facilitating low oxygen tolerance is an ability to dramatically reduce energy expenditure during daytime forays into low oxygen waters. The ETP and Red Sea species reduced aerobic metabolism by more than 50% during exposure to hypoxia. Anaerobic glycolytic energy production, as indicated by whole-animal lactate accumulation, contributed only modestly to the energy deficit. Thus, the total metabolic rate was suppressed by ∼49-64%. Metabolic suppression during diel migrations to depth reduces the metabolic contribution of these species to vertical carbon and nitrogen flux (i.e., the biological pump) by an equivalent amount. Growing evidence suggests that metabolic suppression is a widespread strategy among migrating zooplankton in oxygen minimum zones and may have important implications for the economy and ecology of the oceans. The interacting effects of oxygen and temperature on the metabolism of oceanic species facilitate predictions of changing vertical distribution with climate change.

Temperature is the main factor affecting the distribution of the sympatric Amazon fishes Paracheirodon axelrodi and Paracheirodon simulans. Both species are associated with flooded areas of the Negro river basin; P. axelrodi inhabits waters that do not exceed 30°C, and P. simulans lives at temperatures that can surpass 35°C. The present work aimed to describe the biochemical and physiological adjustments to temperature in those species. We determined the thermal tolerance polygon of species acclimated to four temperatures using critical thermal methodology. We also determined the chronic temperature effects by acclimating the two species at 20, 25, 30, and 35°C and measured the critical oxygen tension (PO2crit) for both species. Additionally, we evaluated the metabolic rate and the enzymes of energy metabolic pathways (CS, MDH, and LDH). Our results showed a larger thermal tolerance polygon, a higher energetic metabolic rate, and higher enzyme levels for P. simulans acclimated to 20 and 35°C compared to P. axelrodi. Paracheirodon simulans also presented a higher hypoxia tolerance, indirectly determined as the PO2cri. Thus, we conclude that the higher metabolic capacity of P. simulans gives this species a better chance to survive at acutely higher temperatures in nature, although it is more vulnerable to chronic exposure.

Life span and aging are substantially modified by natural selection. Across species, higher extrinsic (environmentally related) mortality (and hence shorter life expectancy) selects for the evolution of more rapid aging. However, among populations within species, high extrinsic mortality can lead to extended life span and slower aging as a consequence of condition-dependent survival. Using within-species contrasts of eight natural populations of Nothobranchius fishes in common garden experiments, we demonstrate that populations originating from dry regions (with short life expectancy) had shorter intrinsic life spans and a greater increase in mortality with age, more pronounced cellular and physiological deterioration (oxidative damage, tumor load), and a faster decline in fertility than populations from wetter regions. This parallel intraspecific divergence in life span and aging was not associated with divergence in early life history (rapid growth, maturation) or pace-of-life syndrome (high metabolic rates, active behavior). Variability across four study species suggests that a combination of different aging and life-history traits conformed with or contradicted the predictions for each species. These findings demonstrate that variation in life span and functional decline among natural populations are linked, genetically underpinned, and can evolve relatively rapidly.

Partial migration, in which some individuals of a population migrate while other individuals remain resident, is generally associated with ontogenetic shifts to better feeding areas or as a response to environmental instability, but its underlying mechanisms remain relatively unknown. Brown trout ( Salmo trutta ) exhibit partial migration, with some individuals remaining in freshwater (freshwater resident) while others undertake an anadromous migration, where they spend time at sea before returning to breed in freshwater (migrant). We reared full‐sibling groups of offspring from freshwater‐resident and anadromous brown trout from the same catchment in the laboratory under common garden conditions to examine potential differences in their early development. Freshwater‐resident parents produced eggs that were slower to hatch than those of anadromous parents, but freshwater‐resident offspring were quicker to absorb their yolk and reach the stage of exogenous feeding. Their offspring also had a higher conversion efficiency from the egg stage to the start of exogenous feeding (so were larger by the start of the fry stage) than did offspring from anadromous parents despite no difference in standard metabolic rate, maximal metabolic rate or aerobic scope. Given these differences in early development, we discuss how the migration history of the parents might influence the migration probability of the offspring.

Recent empirical and conceptual papers have highlighted the potential for metabolism to act as a proximate mechanism for behavior that could explain animal personality (consistency over time). Under this hypothesis, individuals with consistently high levels of behavioral activity should also have high resting metabolic rate ( RMR ) as it can reflect capacity to process food and generate energy. We tested for the predicted positive covariance between RMR and three behaviors that differ in energy demands in 30 male guppies, using multivariate mixed models; we repeatedly measured their activity (10 times each), courtship displays (nine times), voracity (10 times), and metabolism (four‐times). Resting metabolic rate (measured overnight in respirometry trials) did not consistently differ among males, whereas initial peak metabolism measured during those same trials ( R = 0.42), and all behaviors were repeatable ( R = 0.33–0.51). RMR declined over time suggesting habituation to the protocol, whereas peak metabolism did not. Initial peak metabolism was negatively correlated with courtship display intensity, and voracity was positively correlated with activity, but all other among‐individual correlations were not significant. We conclude that RMR does not provide a proximate explanation for consistent individual differences in behavior in male guppies, and therefore the potential for independent evolution of these physiological and behavioral traits seems possible. Finally, we identify peak metabolism as a potential measure of the stress response to confinement, which highlights the value of considering various aspects of metabolic rates recording during respirometry trials.

Metabolic rate reflects the ‘pace of life’ in every organism. Metabolic rate is related to an organism's capacity for essential maintenance, growth and reproduction—all of which interact to affect fitness. Although thousands of measurements of metabolic rate have been made, the microevolutionary forces that shape metabolic rate remain poorly resolved. The relationship between metabolic rate and components of fitness are often inconsistent, possibly because these fitness components incompletely map to actual fitness and often negatively covary with each other. Here we measure metabolic rate across ontogeny and monitor its effects on actual fitness (lifetime reproductive output) for a marine bryozoan in the field. We also measure key components of fitness throughout the entire life history including growth rate, longevity and age at the onset of reproduction. We found that correlational selection favours individuals with higher metabolic rates in one stage and lower metabolic rates in the other—individuals with similar metabolic rates in each developmental stage displayed the lowest fitness. Furthermore, individuals with the lowest metabolic rates lived for longer and reproduced more, but they also grew more slowly and took longer to reproduce initially. That metabolic rate is related to the pace of the life history in nature has long been suggested by macroevolutionary patterns but this study reveals the microevolutionary processes that probably generated these patterns.

Population density has recently been suggested to be an important factor influencing metabolic rates and to represent an important ‘third axis’ explaining variation beyond that explained by body mass and temperature. In situations where population density influences food consumption, the immediate effect on metabolism acting through specific dynamic action ( SDA ), and downregulation due to fasting over longer periods, is well understood. However, according to a recent review, previous studies suggest a more general effect of population density per se, even in the absence of such effects. It has been hypothesized that this results from animals performing anticipatory responses (i.e. reduced activity) to expected declines in food availability. Here, we test the generality of this finding by measuring density effects on metabolic rates in 10 clones from two different species of the zooplankton Daphnia ( Daphnia pulex Leydig and D. magna Straus). Using fluorescence‐based respirometry, we obtain high‐precision measures of metabolism. We also identify additional studies on this topic that were not included in the previous review, compare the results and evaluate the potential for measurement bias in all previous studies. We demonstrate significant variation in mass‐specific metabolism among clones within both species. However, we find no evidence for a negative relationship between population density and mass‐specific metabolism. The previously reported pattern also disappeared when we extended the set of studies analysed. We discuss potential reasons for the discrepancy among studies, including two main sources of potential bias (microbial respiration and declining oxygen consumption due to reduced oxygen availability). Only one of the previous studies gives sufficient information to conclude the absence of such biases, and consistent with our results, no effect of density on metabolism was found. We conclude that population density per se does not have a general effect on mass‐specific metabolic rate.

Ongoing climate change is affecting animal physiology in many parts of the world. Using metabolism, the oxygen- and capacity-limitation of thermal tolerance (OCLTT) hypothesis provides a tool to predict the responses of ectothermic animals to variation in temperature, oxygen availability and pH in the aquatic environment. The hypothesis remains controversial, however, and has been questioned in several studies. A positive relationship between aerobic metabolic scope and animal activity would be consistent with the OCLTT but has rarely been tested. Moreover, the performance model and the allocation model predict positive and negative relationships, respectively, between standard metabolic rate and activity. Finally, animal activity could be affected by individual morphology because of covariation with cost of transport. Therefore, we hypothesized that individual variation in activity is correlated with variation in metabolism and morphology. To test this prediction, we captured 23 wild European perch (Perca fluviatilis) in a lake, tagged them with telemetry transmitters, measured standard and maximal metabolic rates, aerobic metabolic scope and fineness ratio and returned the fish to the lake to quantify individual in situ activity levels. Metabolic rates were measured using intermittent flow respirometry, whereas the activity assay involved high-resolution telemetry providing positions every 30 s over 12 days. We found no correlation between individual metabolic traits and activity, whereas individual fineness ratio correlated with activity. Independent of body length, and consistent with physics theory, slender fish maintained faster mean and maximal swimming speeds, but this variation did not result in a larger area (in square metres) explored per 24 h. Testing assumptions and predictions of recent conceptual models, our study indicates that individual metabolism is not a strong determinant of animal activity, in contrast to individual morphology, which is correlated with in situ activity patterns.

Global warming results in increasing water temperature, which may represent a threat to aquatic ectotherms. The rising temperature affects ecology through physiology, by exerting a direct limiting effect on the individual. The mechanism controlling individual thermal tolerance is still elusive, but some evidence shows that the heart plays a central role, and that insufficient transport of oxygen to the respiring tissues may determine the thermal tolerance of animals. In this study, the influence of the heart in thermal limitation was investigated by measurements of aerobic scope in the European eel ( Anguilla anguilla ) together with measurements of cardiac output during rest and activity. Aerobic capacity was not limited by an acutely increased temperature in the European eel. Oxygen demand was met by an increase in heart rate and arteriovenous extraction. These findings suggest that thermal tolerance during exposure to acute temperature changes is not defined by oxygen transport capacity in the eel, and other mechanisms may play a central role in limiting thermal tolerance in these fish.

The relationships among animal form, function and performance are complex, and vary across environments. Therefore, it can be difficult to identify morphological and/or physiological traits responsible for enhancing performance in a given habitat. In fishes, differences in swimming performance across water flow gradients are related to morphological variation among and within species. However, physiological traits related to performance have been less well studied. We experimentally reared juvenile damselfish, Acanthochromis polyacanthus, under different water flow regimes to test 1) whether aspects of swimming physiology and morphology show plastic responses to water flow, 2) whether trait divergence correlates with swimming performance and 3) whether flow environment relates to performance differences observed in wild fish. We found that maximum metabolic rate, aerobic scope and blood haematocrit were higher in wave-reared fish compared to fish reared in low water flow. However, pectoral fin shape, which tends to correlate with sustained swimming performance, did not differ between rearing treatments or collection sites. Maximum metabolic rate was the best overall predictor of individual swimming performance; fin shape and fish total length were 3.3 and 3.7 times less likely than maximum metabolic rate to explain differences in critical swimming speed. Performance differences induced in fish reared in different flow environments were less pronounced than in wild fish but similar in direction. Our results suggest that exposure to water motion induces plastic physiological changes which enhance swimming performance in A. polyacanthus. Thus, functional relationships between fish morphology and performance across flow habitats should also consider differences in physiology.

Non-random mortality associated with commercial and recreational fisheries have the potential to cause evolutionary changes in fish populations. Inland recreational fisheries offer unique opportunities for the study of fisheries induced evolution due to the ability to replicate study systems, limited gene flow among populations, and the existence of unexploited reference populations. Experimental research has demonstrated that angling vulnerability is heritable in Largemouth Bass Micropterus salmoides, and is correlated with elevated resting metabolic rates (RMR) and higher fitness. However, whether such differences are present in wild populations is unclear. This study sought to quantify differences in RMR among replicated exploited and unexploited populations of Largemouth Bass. We collected age-0 Largemouth Bass from two Connecticut drinking water reservoirs unexploited by anglers for almost a century, and two exploited lakes, then transported and reared them in the same pond. Field RMR of individuals from each population was quantified using intermittent-flow respirometry. Individuals from unexploited reservoirs had a significantly higher mean RMR (6%) than individuals from exploited populations. These findings are consistent with expectations derived from artificial selection by angling on Largemouth Bass, suggesting that recreational angling may act as an evolutionary force influencing the metabolic rates of fishes in the wild. Reduced RMR as a result of fisheries induced evolution may have ecosystem level effects on energy demand, and be common in exploited recreational populations globally.

Humans are rapidly altering thermal landscapes, so a central challenge to organismal ecologists is to better understand the thermal niches of ectotherms. However, there is much disagreement over how we should go about this. Some ecologists assume that a statistical model of abundance as a function of habitat temperature provides a sufficient approximation of the thermal niche, but ecophysiologists have shown that the relationship between fitness and temperature can be complicated, and have stressed the need to elucidate the causal mechanisms underlying the response of species to thermal change. Towards this end, we studied the distribution of two crayfishes, Euastacus woiwuru and Euastacus armatus, along an altitudinal gradient, and for both species conducted experiments to determine the temperature-dependence of: (1) aerobic scope (the difference between maximum and basal metabolic rate; purported to be a proxy of the thermal niche); and (2) burst locomotor performance (primarily fuelled using anaerobic pathways). E. woiwuru occupied cooler habitats than E. armatus, but we found no difference in aerobic scope between these species. In contrast, locomotor performance curves differed significantly and strongly between species, with peak locomotor performances of E. woiwuru and E. armatus occurring at ~10 and ~18 °C, respectively. Crayfish from different thermal landscapes may have similar aerobic thermal performance curves but different anaerobic thermal performance curves. Our results support a growing body of literature implying different components of ectotherm fitness have different thermal performance curves, and further challenge our understanding of the ecology and evolution of thermal niches.

The microsporidian L oma morhua infects Atlantic cod ( G adus morhua ) in the wild and in culture and results in the formation of xenomas within the gill filaments, heart and spleen. Given the importance of the two former organs to metabolic capacity and thermal tolerance, the cardiorespiratory performance of cod with a naturally acquired infection of Loma was measured during an acute temperature increase (2 °C h −1 ) from 10 °C to the fish's critical thermal maximum ( CT Max ). In addition, oxygen consumption and swimming performance were measured during two successive critical swimming speed ( U crit ) tests at 10 °C. While Loma infection had a negative impact on cod cardiac function at warm temperatures, and on metabolic capacity in both the CT Max and U crit tests (i.e. a reduction of 30–40%), it appears that the Atlantic cod can largely compensate for these Loma ‐induced cardiorespiratory limitations. For example, (i) CT Max (21.0 ± 0.3 °C) and U crit (~1.75 BL s −1 ) were very comparable to those reported in previous studies using uninfected fish from the same founder population; and (ii) our data suggest that tissue oxygen extraction, and potentially the capacity for anaerobic metabolism, is enhanced in fish infected with this microsporidian.

The oxygen consumption of two groups of 10° C acclimated steelhead trout Oncorhynchus mykiss was measured for 72 h after they were given a 100 µl kg −1 intraperitoneal injection of formalin‐killed Aeromonas salmonicida ( ASAL ) or phosphate‐buffered saline ( PBS ). In addition, plasma cortisol levels were measured in fish from both groups prior to, and 1 and 3 h after, they were given a 30 s net stress. The first group was fed an unaltered commercial diet for 4 weeks, whereas the second group was fed the same diet but with 0·5% (5 g kg −1 ) Aloe vera powder added; A. vera has potential as an immunostimulant for use in aquaculture, but its effects on basal and acute phase response ( APR )‐related metabolic expenditures and stress physiology, are unknown. Injection of ASAL v. PBS had no measurable effect on the of O. mykiss indicating that the APR in this species is not associated with any net increase in energy expenditure. In contrast, incorporating 0·5% A. vera powder into the feed decreased routine metabolic rate by c. 8% in both injection groups and standard metabolic rate in the ASAL ‐injected group (by c. 4 mg O 2 kg −1 h −1; 5%). Aloe vera fed fish had resting cortisol levels that were approximately half of those in fish on the commercial diet ( c. 2·5 v. 5·0 ng ml −1 ), but neither this difference nor those post‐stress reached statistical significance ( P > 0·05).

Many fish encounter hypoxia on a daily cycle, but the physiological effects of intermittent hypoxia are poorly understood. We investigated whether acclimation to constant (sustained) hypoxia or to intermittent diel cycles of nocturnal hypoxia (12 h normoxia: 12 h hypoxia) had distinct effects on hypoxia tolerance or on several determinants of O2 transport and O2 utilization in estuarine killifish. Adult killifish were acclimated to normoxia, constant hypoxia, or intermittent hypoxia for 7 or 28 days in brackish water (4 ppt). Acclimation to both hypoxia patterns led to comparable reductions in critical O2 tension and resting O2 consumption rate, but only constant hypoxia reduced the O2 tension at loss of equilibrium. Constant (but not intermittent) hypoxia decreased filament length and the proportion of seawater-type mitochondrion-rich cells in the gills (which may reduce ion loss and the associated costs of active ion uptake), increased blood haemoglobin content, and reduced the abundance of oxidative fibres in the swimming muscle. In contrast, only intermittent hypoxia augmented the oxidative and gluconeogenic enzyme activities in the liver and increased the capillarity of glycolytic muscle, each of which should facilitate recovery between hypoxia bouts. Neither exposure pattern affected muscle myoglobin content or the activities of metabolic enzymes in the brain or heart, but intermittent hypoxia increased brain mass. We conclude that the pattern of hypoxia exposure has an important influence on the mechanisms of acclimation, and that the optimal strategies used to cope with intermittent hypoxia may be distinct from those for coping with constant hypoxia.

This study investigated the effects of seaweed dietary supplementation on measures of fish performance including aerobic metabolism, digestive enzymes activity, innate immune status, oxidative damage, and growth rate using European seabass (Dicentrarchus labrax). Fish were fed for 49 days with three different diets: a control diet (CTRL), a Gracilaria-supplemented diet (GR7.5), and a mixed diet (Mix) composed of Gracilaria, Fucus, and Ulva genera representatives. All diets were isoenergetic (22 kJ g−1 adjusted for dry matter (DM)), isoproteic (47 %DM), and isolipidic (18 %DM) and tested in triplicate groups of 20 fish (initial body weight 25.5 ± 4.1 g). Final results showed similar growth rates and digestive activities between diets. Maximum and standard metabolic rates and aerobic metabolic scope revealed comparable results for the three diets. In contrast, fish fed with GR7.5 exhibited elevated routine metabolic rate (190.7 mg O2 kg−1 h−1). Fish fed with the GR7.5 and Mix diets had lower alternative complement pathway (ACH50) (62.5 and 63 units mL−1 respectively) than CTRL (84 units mL−1) GR7.5 increased lipid peroxidation and cholinesterase levels, as well as glutathione s-transferase activity. Mix diet increased glutathione reductase activity when compared to CTRL. Collectively, our findings suggest that dietary seaweed supplementation may alter seabass metabolic rate, innate immune, and antioxidant responses without compromising growth parameters.

Tropical inland fishes are predicted to be especially vulnerable to thermal stress because they experience small temperature fluctuations that may select for narrow thermal windows. In this study, we measured resting metabolic rate (RMR), critical oxygen tension (P crit) and critical thermal maximum (CTMax) of the widespread African cichlid (Pseudocrenilabrus multicolor victoriae) in response to short-term acclimation to temperatures within and above their natural thermal range. Pseudocrenilabrus multicolor collected in Lake Kayanja, Uganda, a population living near the upper thermal range of the species, were acclimated to 23, 26, 29 and 32°C for 3 days directly after capture, and RMR and P crit were then quantified. In a second group of P. multicolor from the same population, CTMax and the thermal onset of agitation were determined for fish acclimated to 26, 29 and 32°C for 7 days. Both RMR and P crit were significantly higher in fish acclimated to 32°C, indicating decreased tolerance to hypoxia and increased metabolic requirements at temperatures only slightly (∼1°C) above their natural thermal range. The CTMax increased with acclimation temperature, indicating some degree of thermal compensation induced by short-term exposure to higher temperatures. However, agitation temperature (likely to represent an avoidance response to increased temperature during CTMax trials) showed no increase with acclimation temperature. Overall, the results of this study demonstrate that P. multicolor is able to maintain its RMR and P crit across the range of temperatures characteristic of its natural habitat, but incurs a higher cost of resting metabolism and reduced hypoxia tolerance at temperatures slightly above its present range.

The harvest of animals by humans may constitute one of the strongest evolutionary forces affecting wild populations. Vulnerability to harvest varies among individuals within species according to behavioural phenotypes, but we lack fundamental information regarding the physiological mechanisms underlying harvest-induced selection. It is unknown, for example, what physiological traits make some individual fish more susceptible to capture by commercial fisheries. Active fishing methods such as trawling pursue fish during harvest attempts, causing fish to use both aerobic steady-state swimming and anaerobic burst-type swimming to evade capture. Using simulated trawling procedures with schools of wild minnows Phoxinus phoxinus, we investigate two key questions to the study of fisheries-induced evolution that have been impossible to address using large-scale trawls: (i) are some individuals within a fish shoal consistently more susceptible to capture by trawling than others?; and (ii) if so, is this related to individual differences in swimming performance and metabolism? Results provide the first evidence of repeatable variation in susceptibility to trawling that is strongly related to anaerobic capacity and swimming ability. Maximum aerobic swim speed was also negatively correlated with vulnerability to trawling. Standard metabolic rate was highest among fish that were least vulnerable to trawling, but this relationship probably arose through correlations with anaerobic capacity. These results indicate that vulnerability to trawling is linked to anaerobic swimming performance and metabolic demand, drawing parallels with factors influencing susceptibility to natural predators. Selection on these traits by fisheries could induce shifts in the fundamental physiological makeup and function of descendent populations.

Tradeoffs between hypoxia tolerance and aerobic exercise performance appear to exist in some fish taxa, even though both of these traits are often associated with a high O2 transport capacity. We examined the physiological basis for this potential tradeoff in four species of sunfish from the family Centrarchidae. Hypoxia tolerance was greatest in rock bass, intermediate in pumpkinseed and bluegill, and lowest in largemouth bass, based on measurements of critical O2 tension (Pcrit) and O2 tension at loss of equilibrium (PO2 at LOE). Consistent with there being a tradeoff between hypoxia tolerance and aerobic exercise capacity, the least hypoxia-tolerant species had the highest critical swimming speed (Ucrit) during normoxia and suffered the greatest decrease in Ucrit in hypoxia. There was also a positive correlation between Ucrit in normoxia and PO2 at LOE, which remained significant after accounting for phylogeny using phylogenetically independent contrasts. Several sub-organismal traits appeared to contribute to both hypoxia tolerance and aerobic exercise capacity (reflected by traits that were highest in both rock bass and largemouth bass), such as the gas-exchange surface area of the gills, the pH sensitivity of haemoglobin-O2 affinity, and the activities of lactate dehydrogenase and the gluconeogenic enzyme phosphoenolpyruvate carboxykinase in the liver. Some other sub-organismal traits were uniquely associated with either hypoxia tolerance (low sensitivity of haemoglobin-O2 affinity to organic phosphates, high pyruvate kinase and lactate dehydrogenase activities in the heart) or aerobic exercise capacity (capillarity and fibre size of the axial swimming muscle). Therefore, the cumulative influence of a variety of respiratory and metabolic traits can result in physiological tradeoffs associated with the evolution of hypoxia tolerance and aerobic exercise performance in fish.

Sexual coercion of females by males is widespread across sexually reproducing species. It stems from a conflict of interest over reproduction and exerts selective pressure on both sexes. For females, there is often a significant energetic cost of exposure to male sexually coercive behaviours. Our understanding of the efficiency of female resistance to male sexually coercive behaviour is key to understanding how sexual conflict contributes to population level dynamics and ultimately to the evolution of sexually antagonistic traits. Overlooked within this context are plastic physiological responses of traits within the lifetime of females that could moderate the energetic cost imposed by coercive males. Here, we examined whether conflict over the frequency and timing of mating between male and female guppies Poecilia reticulata can induce changes in swimming performance and aerobic capacity in females as they work to escape harassment by males. Females exposed to higher levels of harassment over a 5‐month period used less oxygen to swim at a given speed, but displayed no difference in resting metabolic rate, maximal metabolic rate, maximal sustained swimming speed or aerobic scope compared to females receiving lower levels of harassment. The observed increase in swimming efficiency is at least partially related to differences in swimming mechanics, likely brought on by a training effect of increased activity, as highly harassed females spent less time performing pectoral fin‐assisted swimming. Sexual conflict results in sexually antagonistic traits that impose a variety of costs, but our results show that females can reduce costs through phenotypic plasticity. It is also possible that phenotypic plasticity in swimming physiology or mechanics in response to sexual coercion can potentially give females more control over matings and affect which male traits are under selection.

Swimming exercise at optimal speed may optimize growth performance of yellowtail kingfish in a recirculating aquaculture system. Therefore, optimal swimming speeds (Uopt in m s-1 or body lengths s-1, BL s-1) were assessed and then applied to determine the effects of long-term forced and sustained swimming at Uopt on growth performance of juvenile yellowtail kingfish. Uopt was quantified in Blazka-type swim-tunnels for 145 mm, 206 mm and 311 mm juveniles resulting in values of: 1) 0.70 m s-1 or 4.83 BL s-1, 2) 0.82 m s-1 or 3.25 BL s-1 and 3) 0.85 m s-1 or 2.73 BL s-1. Combined with literature data from larger fish, a relation of Uopt (BL s-1) = 234.07(BL)-0.779 (R2= 0.9909) was established for this species. Yellowtail kingfish, either forced to perform sustained swimming exercise at an optimal speed of 2.46 BL s-1 (‘swimmers’) or allowed to perform spontaneous activity at low water flow (‘resters’) in a newly designed 3,600 L oval flume (with flow created by an impeller driven by an electric motor), were then compared. At the start of the experiment, ten fish were sampled representing the initial condition. After 18 days, swimmers (n= 23) showed a 92% greater increase in BL and 46% greater increase in BW as compared to resters (n= 23). As both groups were fed equal rations, feed conversion ratio (FCR) for swimmers was 1.21 vs. 1.74 for resters. Doppler ultrasound imaging showed a statistically significant higher blood flow (31%) in the ventral aorta of swimmers vs. resters (44 ± 3 mL min-1 vs. 34 ± 3 mL min-1, respectively, under anesthesia). Thus growth performance can be rapidly improved by optimal swimming, without larger feed investments.

The objectives of this study were (1) to establish egg selenium (Se) toxicity thresholds for mortality and deformities in early life stages of zebrafish (Danio rerio) after exposure to excess selenomethionine (SeMet, the dominant chemical species of Se in diets) via in ovo maternal transfer and (2) to investigate the persistent effects of developmental exposure to excess SeMet on swim performance and metabolic capacities in F1-generation adult zebrafish. Adult zebrafish were fed either control food (1.3 μg Se/g, dry mass or d.m.) or food spiked with increasing measured concentrations of Se (3.4, 9.8, or 27.5 μg Se/g, d.m.) in the form of SeMet for 90 d. In ovo exposure to SeMet increased mortality and deformities in larval zebrafish in a concentration-dependent fashion with threshold egg Se concentrations (EC10s) of 7.5 and 7.0 μg Se/g d.m., respectively. Impaired swim performance and greater respiration and metabolic rates were observed in F1-generation zebrafish exposed in ovo to 6.8 and 12.7 μg Se/g d.m and raised to adulthood in clean water. A species sensitivity distribution (SSD) based on egg Se developmental toxicity thresholds suggests that zebrafish are the most sensitive fish species studied to date.

Waters in urban areas often experience hypoxic events due to combined sewer overflows, which have the potential to negatively affect aquatic biota. Despite these hypoxic events, many urban areas have diverse fish assemblages, suggesting hypoxia has a minimal impact. Data to quantify the impacts of aquatic hypoxia in urban systems are currently lacking. The current study sought to define how rain‐induced hypoxia affected the movement, distribution, and physiology of individual Largemouth Bass Micropterus salmoides residing in the Chicago Area Waterway System (CAWS), an urban area prone to episodes of hypoxia. Following the onset of hypoxic events, the likelihood of Largemouth Bass remaining in hypoxic water was reduced, but fish did not completely avoid hypoxic areas. This suggests that hypoxia exerts only a moderate influence on the movement of Largemouth Bass. Field sampling showed that Largemouth Bass from the site prone to hypoxia were not in poor nutritional condition and were not suffering from chronic stress, relative to compared with those from reference sites. Field sampling also showed that fish from the CAWS displayed an improved capability to transport oxygen in the blood compared with individuals from control sites. Following a low‐oxygen challenge in the laboratory, fish from the CAWS also displayed elevated levels of oxygen transport capabilities compared with fish from some control sites. Together, results suggest that hypoxic events have limited behavioral consequences for Largemouth Bass, and in fact, Largemouth Bass in our study may have developed an improved ability to tolerate hypoxia, which would allow them to persist in hypoxia‐prone areas.

It has recently been suggested that general rules of change in ecological communities might be found through the development of functional relationships between species traits and performance. The physiological, behavioural and life-history traits of fishes are often organised along a fast-slow lifestyle continuum (FSLC). With respect to resistance (capacity for population to resist change) and resilience (capacity for population to recover from change) to environmental hypoxia, the literature suggests that traits enhancing resilience may come at the expense of traits promoting resistance to hypoxia; a trade-off may exist. Here I test whether three fishes occupying different positions along the FSLC trade-off resistance and resilience to environmental hypoxia. Static respirometry experiments were used to determine resistance, as measured by critical oxygen tension (Pcrit), and capacity for (RC) and magnitude of metabolic reduction (RM). Swimming respirometry experiments were used to determine aspects of resilience: critical (Ucrit) and optimal swimming speed (Uopt), and optimal cost of transport (COTopt). Results pertaining to metabolic reduction suggest a resistance gradient across species described by the inequality Melanotaenia fluviatilis (fast lifestyle) < Hypseleotris sp. (intermediate lifestyle) < Mogurnda adspersa (slow lifestyle). The Ucrit and COTopt data suggest a resilience gradient described by the reverse inequality, and so the experiments generally indicate that three fishes occupying different positions on the FSLC trade-off resistance and resilience to hypoxia. However, the scope of inferences that can be drawn from an individual study is narrow, and so steps towards general, trait-based rules of fish community change along environmental gradients are discussed.

Muscular activity patterns in red and white muscles linked to oxygen consumption were studied during critical swimming tests in the sea bass (Dicentrarchus labrax Linnaeus 1758). The species is one of the most important for Mediterranean Sea aquaculture. A sigmoid model was used to fit both the oxygen consumption and red muscle activity while the white muscle activity pattern was described by an exponential model. Red muscle reaches an activation plateau close to critical swimming speed mostly due to the oxygen diffusion velocity in tissues. The exponential activation of white muscle appears to be linked to short and sudden periods of great energy need to cope with adverse conditions such as predation and escape. Both oxygen consumption and muscular activity were found to be size dependent. The bioenergetics of sea bass was modelled based on fish mass and swimming speed to predict the minimum and maximum speed as well as the mass-specific active metabolic rate and standard metabolic rate. An important finding was that contrary to other well-known species, swimming at subcritical speeds in sea bass involves both red and white muscle in different proportions.

The character and magnitude of predation by the invasive, ectothermic Pacifastacus leniusculus, a crayfish widely introduced to Europe and Japan from North America, on the eggs of coregonid fishes, vendace Coregonus albula and whitefish Coregonus lavaretus were examined by experimentation, modelling and field data. The present results showed that P. leniusculus has the potential to be very efficient predator of fish eggs under winter conditions, but the predation by P. leniusculus did not significantly decrease production of coregonid larvae during the years with a high P. leniusculus population in the study lake. Hence, the mortality caused by the novel invertebrate predator appeared to compensate for other yet unexplored mortality factors instead of having an additive effect on the present salmonids.

To quantify cardiorespiratory response to experimental anaemia in rainbow trout Oncorhynchus mykiss, a 24 h phenylhydrazine treatment was used to reduce haematocrit to almost one third of its initial value over 4–5 days. In response, relative blood velocity in the ventral aorta (an index of cardiac output) progressively increased to more than double to its normocythaemic value and there was no significant change in routine oxygen uptake. Thus, the primary compensatory response to anaemia was an increase in cardiac output.

The present study tested the hypothesis that zebrafish (Danio rerio) aquaporin-1a1 (AQP1a1) serves as a multi-functional channel for the transfer of the small gaseous molecules, CO2 and ammonia, as well as water, across biological membranes. Zebrafish embryos were microinjected with a translation-blocking morpholino oligonucleotide targeted to AQP1a1. Knockdown of AQP1a1 significantly reduced rates of CO2 and ammonia excretion, as well as water fluxes, in larvae at 4 days post fertilization (dpf). Because AQP1a1 is expressed both in ionocytes present on the body surface and in red blood cells, the haemolytic agent phenylhydrazine was used to distinguish between the contributions of AQP1a1 to gas transfer in these two locations. Phenylhydrazine treatment had no effect on AQP1a1-linked excretion of CO2 or ammonia, providing evidence that AQP1a1 localized to the yolk sac epithelium, rather than red blood cell AQP1a1, is the major site of CO2 and ammonia movements. The possibility that AQP1a1 and the rhesus glycoprotein Rhcg1, which also serves as a dual CO2 and ammonia channel, act in concert to facilitate CO2 and ammonia excretion was explored. Although knockdown of each protein did not affect the abundance of mRNA and protein of the other protein under control conditions, impairment of ammonia excretion by chronic exposure to high external ammonia triggered a significant increase in the abundance of AQP1a1 mRNA and protein in 4 dpf larvae experiencing Rhcg1 knockdown. Collectively, these results suggest that AQP1a1 in zebrafish larvae facilitates the movement of CO2 and ammonia, as well as water, in a physiologically relevant fashion.

The timing, success and energetics of fish embryonic development are strongly influenced by temperature. However, it is unclear if there are developmental periods, or critical windows, when oxygen use, survival and hatchling phenotypic characteristics are particularly influenced by changes in the thermal environment. Therefore, we examined the effects of constant incubation temperature and thermal shifts on survival, hatchling phenotype, and cost of development in lake whitefish (Coregonus clupeaformis) embryos. We incubated whitefish embryos at control temperatures of 2, 5, or 8 °C, and shifted embryos across these three temperatures at the end of gastrulation or organogenesis. We assessed hatch timing, mass at hatch, and yolk conversion efficiency (YCE). We determined cost of development, the amount of oxygen required to build a unit of mass, for the periods from fertilization–organogenesis, organogenesis–fin flutter, fin flutter–hatch, and for total development. An increase in incubation temperature decreased time to 50 % hatch (164 days at 2 °C, 104 days at 5 °C, and 63 days at 8 °C), survival decreased from 55 % at 2 °C, to 38 % at 5 °C, and 17 % at 8 °C, and hatchling yolk-free dry mass decreased from 1.27 mg at 2 °C to 0.61 mg at 8 °C. Thermal shifts altered time to 50 % hatch and hatchling yolk-free dry mass and revealed a critical window during gastrulation in which a temperature change reduced survival. YCE decreased and cost of development increased with increased incubation temperature, but embryos that hatched at 8 °C and were incubated at colder temperatures during fertilization–organogenesis had reduced cost. The relationship between cost of development and temperature was altered during fin flutter–hatch, indicating it may be a critical window during which temperature has the greatest impact on energetic processes. The increase in cost of development with an increase in temperature has not been documented in other fishes and suggests whitefish embryos are more energy efficient at colder temperatures.

Sustained swimming at moderate speeds is considered beneficial in terms of the productive performance of salmonids, but the causative mechanisms have yet to be unequivocally established. In the present study, the effects of moderate exercise on the bioenergetics of rainbow trout were assessed during a 15 week growth experiment, in which fish were reared at three different current speeds: 1 BL s(-1), 0.5 BL s(-1) and still water (≈ 0 BL s(-1)). Randomly selected groups of 100 fish were distributed among twelve 600 L tanks and maintained on a restricted diet regime. Specific growth rate (SGR) and feed conversion ratio (FCR) were calculated from weight and length measurements every 3 weeks. Routine metabolic rate (RMR) was measured every hour as rate of oxygen consumption in the tanks, and was positively correlated with swimming speed. Total ammonia nitrogen (TAN) excretion rates showed a tendency to decrease with increasing swimming speeds, yet neither they nor the resulting nitrogen quotients (NQ) indicated that swimming significantly reduced the fraction of dietary protein used to fuel metabolism. Energetic budgets revealed a positive correlation between energy expenditure and the current speed at which fish were reared, fish that were forced to swim and were fed restrictively consequentially had poorer growth and feed utilization. The results show that for rainbow trout, water current can negatively affect growth despite promoting minor positive changes in substrate utilization. We hypothesize that this may be the result of either a limited dietary energy supply from diet restriction being insufficient for both covering the extra costs of swimming and supporting enhanced growth.

Seahorses are currently facing great challenges in the wild, including habitat degradation and overexploitation, and how they will endure additional stress from rapid climate change has yet to be determined. Unlike most fishes, the poor swimming skills of seahorses, along with the ecological and biological constraints of their unique lifestyle, place great weight on their physiological ability to cope with climate changes. In the present study, we evaluate the effects of ocean warming (+4°C) and acidification (ΔpH = -0.5 units) on the physiological and behavioural ecology of adult temperate seahorses, Hippocampus guttulatus. Adult seahorses were found to be relatively well prepared to face future changes in ocean temperature, but not the combined effect of warming and acidification. Seahorse metabolism increased normally with warming, and behavioural and feeding responses were not significantly affected. However, during hypercapnia the seahorses exhibited signs of lethargy (i.e. reduced activity levels) combined with a reduction of feeding and ventilation rates. Nonetheless, metabolic rates were not significantly affected. Future ocean changes, particularly ocean acidification, may further threaten seahorse conservation, turning these charismatic fishes into important flagship species for global climate change issues.

Global increase in sea temperatures has been suggested to facilitate the incoming and spread of tropical invaders. The increasing success of these species may be related to their higher physiological performance compared with indigenous ones. Here, we determined the effect of temperature on the aerobic metabolic scope (MS) of two herbivorous fish species that occupy a similar ecological niche in the Mediterranean Sea: the native salema (Sarpa salpa) and the invasive marbled spinefoot (Siganus rivulatus). Our results demonstrate a large difference in the optimal temperature for aerobic scope between the salema (21.8°C) and the marbled spinefoot (29.1°C), highlighting the importance of temperature in determining the energy availability and, potentially, the distribution patterns of the two species. A modelling approach based on a present-day projection and a future scenario for oceanographic conditions was used to make predictions about the thermal habitat suitability (THS, an index based on the relationship between MS and temperature) of the two species, both at the basin level (the whole Mediterranean Sea) and at the regional level (the Sicilian Channel, a key area for the inflow of invasive species from the Eastern to the Western Mediterranean Sea). For the present-day projection, our basin-scale model shows higher THS of the marbled spinefoot than the salema in the Eastern compared with the Western Mediterranean Sea. However, by 2050, the THS of the marbled spinefoot is predicted to increase throughout the whole Mediterranean Sea, causing its westward expansion. Nevertheless, the regional-scale model suggests that the future thermal conditions of Western Sicily will remain relatively unsuitable for the invasive species and could act as a barrier for its spread westward. We suggest that metabolic scope can be used as a tool to evaluate the potential invasiveness of alien species and the resilience to global warming of native species.

Standard metabolic rates (SMR) were measured in brown bullheads (Ameiurus nebulosus) collected from two locations of the Detroit River, North America, representative of highly contaminated and uncontaminated areas. Measurements of SMR were completed within 10 days of fish collections (acute trials), for fish held in a common pond environment for 1 year (clearance trials) and for F 1 generation fish raised in the pond environment (F 1 study). SMRs were significantly higher (26%) in fish from the contaminated area during acute trials. Both populations showed large decreases in SMR (49% to 52%) following clearance; however, differences between populations were still evident. There were no significant differences in SMRs between populations for F 1 fish. This study demonstrates that Detroit River brown bullheads from contaminated areas have higher metabolic rates than fish from clean locations, and this metabolic effect is retained for long durations after fish are placed in a common environment. The loss of metabolic differences in F 1 offspring indicates that the observed differences in SMR were acclimation-based and not adaptive or related to maternal effects.

We assessed the metabolic response of juvenile Atlantic salmon (Salmo salar; JAS) originating from two rivers with different natural thermal regimes to different acclimation temperature (15 or 20 °C) and diel temperature fluctuation (constant: ±0.5 °C; fluctuating: ±2.5 °C). Diel temperature fluctuation (15 ± 2.5 °C) near the thermal optimum (16 °C) for the species did not influence standard metabolic rate (SMR) compared with JAS acclimated to a constant temperature of 15 °C. Diel temperature fluctuation at 20 ± 2.5 °C increased SMR of JAS from the warmer river by 33.7% compared with the same fish acclimated to a constant temperature of 20 °C. SMR of JAS from the cooler river held at fluctuating conditions had SMR that were 8% lower than SMR at constant conditions. The results suggest that the mean temperature to which JAS is exposed may affect their responses to diel temperature fluctuation and that this response may vary between populations originating from rivers with different natural thermal regimes. Results were used to develop the first empirical SMR model for JAS subjected to diel temperature fluctuation using fish mass (3–36 g wet) and temperature (12.5–22.5 °C) as explanatory variables.

Within species, larger offspring typically outperform smaller offspring. While the relationship between offspring size and performance is ubiquitous, the cause of this relationship remains elusive. By linking metabolic and life-history theory, we provide a general explanation for why larger offspring perform better than smaller offspring. Using high-throughput respirometry arrays, we link metabolic rate to offspring size in two species of marine bryozoan. We found that metabolism scales allometrically with offspring size in both species: while larger offspring use absolutely more energy than smaller offspring, larger offspring use proportionally less of their maternally derived energy throughout the dependent, non-feeding phase. The increased metabolic efficiency of larger offspring while dependent on maternal investment may explain offspring size effects—larger offspring reach nutritional independence (feed for themselves) with a higher proportion of energy relative to structure than smaller offspring. These findings offer a potentially universal explanation for why larger offspring tend to perform better than smaller offspring but studies on other taxa are needed.

Intraspecific variation and trade-off in aerobic and anaerobic traits remain poorly understood in aquatic locomotion. Using gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata), both axial swimmers, this study tested four hypotheses: (1) gait transition from steady to unsteady (i.e., burst-assisted) swimming is associated with anaerobic metabolism evidenced as excess post exercise oxygen consumption (EPOC); (2) variation in swimming performance (critical swimming speed; U crit) correlates with metabolic scope (MS) or anaerobic capacity (i.e., maximum EPOC); (3) there is a trade-off between maximum sustained swimming speed (U sus) and minimum cost of transport (COTmin); and (4) variation in U sus correlates positively with optimum swimming speed (U opt; i.e., the speed that minimizes energy expenditure per unit of distance traveled). Data collection involved swimming respirometry and video analysis. Results showed that anaerobic swimming costs (i.e., EPOC) increase linearly with the number of bursts in S. aurata, with each burst corresponding to 0.53 mg O2 kg(-1). Data are consistent with a previous study on striped surfperch (Embiotoca lateralis), a labriform swimmer, suggesting that the metabolic cost of burst swimming is similar across various types of locomotion. There was no correlation between U crit and MS or anaerobic capacity in S. aurata indicating that other factors, including morphological or biomechanical traits, influenced U crit. We found no evidence of a trade-off between U sus and COTmin. In fact, data revealed significant negative correlations between U sus and COTmin, suggesting that individuals with high U sus also exhibit low COTmin. Finally, there were positive correlations between U sus and U opt. Our study demonstrates the energetic importance of anaerobic metabolism during unsteady swimming, and provides intraspecific evidence that superior maximum sustained swimming speed is associated with superior swimming economy and optimum speed.

Anthropogenic chemicals in the environment during critical periods could potentially affect the physiology of the economically valuable American lobster ( Homarus americanus ). Endosulfan (Thiodan™ WP) is a broad-spectrum organochlorine insecticide widely used in agricultural areas in Canada that significantly affects survival and growth of lobster larvae based on acute exposure studies. To detect more subtle physiological effects of an acute (96-h) sub-lethal level (0.1 μg·L -1 ) of formulated endosulfan exposure on early juvenile lobsters, investigations of metabolic rates, growth and the tissue structure of the hepatopancreas were conducted on animals that molted following the exposure. The standard and active metabolic rates were not significantly affected, but their differential, defined as the metabolic scope (MS) was significantly decreased by 25% for exposed animals. Lobster growth and survival were not affected. For the exposed lobsters, minor alterations of the digestive cell structures were observed. These results suggest that the decrease in MS for exposed juvenile lobsters could have consequences in terms of survival in the wild by impairing their abilities to find a shelter, food or protect themselves from predators. The growth and survival in laboratory conditions suggests that lobsters may adjust their metabolism to pesticide exposure by maintaining a positive energy balance with some compensatory mechanisms; however, this may not be possible in their natural environment. This study suggests that conclusions based solely on lethal toxicity assays could be misleading for sublethal effects of contaminants on marine organisms, which could be investigated more thoroughly using an integrated approach based on physiological indicators.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 496:19-32 (2014) - DOI: https://doi.org/10.3354/meps10528 Theme Section: Tracking fitness in marine vertebrates Estimating activity-specific energy expenditure in a teleost fish, using accelerometer loggers Serena Wright1,2,*, Julian D. Metcalfe1, Stuart Hetherington1, Rory Wilson2 1Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, Lowestoft NR33 0HT, UK 2Swansea University, Singleton Park, Swansea SA2 8PP, UK *Corresponding author: serena.wright@cefas.co.uk ABSTRACT: The ability to define and quantify the behaviour and energetic costs of different activities is fundamental to a full understanding of fish ecology and movement, but monitoring activity and measuring energy expenditure in fish in the field is problematic. New telemetry methods using data loggers that incorporate tri-axial accelerometers promise to provide a method for simultaneously recording the behaviour and activity-specific energy use in both the laboratory and field. Using electronic data loggers equipped with tri-axial accelerometers we have measured dynamic body acceleration (DBA) during aerobic exercise in European sea bass Dicentrarchus labrax whilst swimming in a swim-tunnel respirometer at ambient water temperatures of between 5.5 and 17.5°C. For all individuals, dynamic body acceleration (both vectorial dynamic body acceleration [VeDBA] and overall dynamic body acceleration [ODBA]) scaled linearly with oxygen consumption and as a function of ambient temperature. When the 2 DBA metrics were compared, VeDBA was not significantly different from ODBA, though the value for Akaike’s information criterion was lower for VeDBA (indicating a better fit for the VeDBA model). In this paper, we provide further evidence to support the use of acceleration as a means to quantify the activity-specific energetic costs of swimming in teleosts and highlight some of the problems associated with monitoring the activity and metabolic rate of fish in restricted laboratory conditions. KEY WORDS: Acceleration · Fish · Energetics · Temperature · Respirometry Full text in pdf format PreviousNextCite this article as: Wright S, Metcalfe JD, Hetherington S, Wilson R (2014) Estimating activity-specific energy expenditure in a teleost fish, using accelerometer loggers. Mar Ecol Prog Ser 496:19-32. https://doi.org/10.3354/meps10528 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 496. Online publication date: January 27, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

The relationship between tail (or wing) beat frequency (ftail), amplitude (A) and forward velocity (U) in animals using oscillatory propulsion, when moving at a constant cruising speed, converges upon an optimum range of the Strouhal number (St=ftail·A/U). Previous work, based on observational data and supported by theory, shows St falling within the broad optimum range (0.2

Aryl hydrocarbon receptor (AhR) agonists are known to cause lethal cardiovascular deformities in fish after developmental exposure. Acute adult fish toxicity of AhR agonists is thought to be minimal, but limited evidence suggests sublethal effects may also involve the cardiac system in fish. In the present study, adult zebrafish (Danio rerio) were aqueously exposed to solvent control or three nominal concentrations of the commonly used model AhR agonist, β-naphthoflavone (BNF), for 48 h. Following exposure, fish were subjected to echocardiography to determine cardiac function or swimming tests with concurrent oxygen consumption measurement. Critical swimming speed and standard metabolic rate were not significantly changed, while active metabolic rate decreased with increasing BNF exposure, reaching statistical significance at the highest BNF exposure. Factorial aerobic scope was the most sensitive end-point and was decreased at even lower BNF concentrations, indicating a reduced aerobic capacity after acute AhR agonist exposure in adult fish. The highest BNF concentration caused a significant decrease in cardiac output, while increasing the ratio of atrial to ventricular heart rate (indicating atrioventricular conduction blockade). In conclusion, the effect of acute BNF exposure on zebrafish metabolic capacity and cardiac function is likely to be physiologically important given that fish have a critical need for adequate oxygen to fuel essential survival behaviors such as swimming, growth, and reproduction. Future studies should be directed at examining the effects of other polycyclic aromatic hydrocarbons on fish cardiorespiratory function to determine whether their effects and modes of action are similar to BNF.

The Deepwater Horizon incident likely resulted in exposure of commercially and ecologically important fish species to crude oil during the sensitive early life stages. We show that brief exposure of a water-accommodated fraction of oil from the spill to mahi-mahi as juveniles, or as embryos/larvae that were then raised for ∼25 days to juveniles, reduces their swimming performance. These physiological deficits, likely attributable to polycyclic aromatic hydrocarbons (PAHs), occurred at environmentally realistic exposure concentrations. Specifically, a 48 h exposure of 1.2 ± 0.6 μg L(-1) ΣPAHs (geometric mean ± SEM) to embryos/larvae that were then raised to juvenile stage or a 24 h exposure of 30 ± 7 μg L(-1) ΣPAHs (geometric mean ± SEM) directly to juveniles resulted in 37% and 22% decreases in critical swimming velocities (Ucrit), respectively. Oil-exposed larvae from the 48 h exposure showed a 4.5-fold increase in the incidence of pericardial and yolk sac edema relative to controls. However, this larval cardiotoxicity did not manifest in a reduced aerobic scope in the surviving juveniles. Instead, respirometric analyses point to a reduction in swimming efficiency as a potential alternative or contributing mechanism for the observed decreases in Ucrit.

California’s populations of hardhead Mylopharodon conocephalus, a species of special concern, have declined, possibly due to dam construction with consequent temperature and water-velocity changes, and the introduction of non-native species. Environmental temperature effects on this large (to 60 cm SL) cyprinid, and its swimming abilities, are not well known. To address these deficiencies and to assist conservation efforts, we measured resting and swimming metabolic rates of adult and juvenile hardhead acclimated to four temperatures (11, 16, 21, or 25 °C). Resting metabolic rates (RMR, mg O2 kg−0.79 h−1) generally increased with acclimation temperature, in adults and juveniles, with low to moderate thermal sensitivity (Q10 range: 1.33–2.04). Swimming metabolic rates, in Brett-style respirometers, of adults ranged from 209 to 1342 mg O2 kg−1 h−1 at velocities from 30 to 90 cm s−1, and juveniles ranged from 393 to 769 mg O2 kg−1 h−1 from 10 to 50 cm s−1. Adults were lethargic at 11 °C and juveniles frequently refused to swim at 11 and 16 °C, but all fish swam well at 21 and 25 °C. These results suggest that hardhead are well-suited for sustained aerobic activity over a range of flow velocities, at moderate temperatures (ca. 16 to 21 °C). However, juveniles, emerging in spring, may not be able to perform in cold water and/or high flow velocities, providing a caution to dam managers and regulators to avoid spring and summer operations whereby juveniles experience conditions outside of those occurring in unregulated rivers.

To determine the factors that may contribute to the poor survival of triploid (3n) rainbow trout (Oncorhynchus mykiss) in lake stocking programs, we compared the physiology and responses to environmental challenges of four wild strains and one domestic strain of diploid (2n) and 3n juvenile rainbow trout. Over four successive years, wild trout were caught from nature, spawned, and progeny were reared in a hatchery along with hatchery-bred domestic trout. Offspring of each strain were raised for up to 12 months as both 2n and 3n, and growth rate, critical swimming speed, routine oxygen consumption rate, critical oxygen tensions, thermal tolerance, and hypoxia tolerance were assessed in a laboratory setting. Cohorts of the 2008, 2009, and 2010 wild strains were also stocked into two experimental lakes and recaptured as adults using traps and fyke nets in 2011 for laboratory analysis. In the juvenile trout, the only measure of performance to show a consistent difference between 2n and 3n individuals across all strains was hypoxia tolerance, where 3n trout had a shorter time to loss of equilibrium (LOE) at 16 Torr than their 2n counterparts, but this effect was not seen in adult, lake-reared trout. Strain had a significant effect on specific growth rate, critical swimming speed (U crit ), and time to LOE in hypoxia, although the effects of strain on these variables was not consistent from year to year. Overall, this study suggests that poorer hypoxia tolerance in 3n trout compared with 2n trout may be a contributing factor to the higher lake stocking mortalities in 3n trout.

Sharks are one of the most threatened groups of marine animals worldwide, mostly owing to overfishing and habitat degradation/loss. Although these cartilaginous fish have evolved to fill many ecological niches across a wide range of habitats, they have limited capability to rapidly adapt to human-induced changes in their environments. Contrary to global warming, ocean acidification was not considered as a direct climate-related threat to sharks. Here we show, for the first time, that an early ontogenetic acclimation process of a tropical shark ( Chiloscyllium punctatum ) to the projected scenarios of ocean acidification (ΔpH = 0.5) and warming (+4°C; 30°C) for 2100 elicited significant impairments on juvenile shark condition and survival. The mortality of shark embryos at the present-day thermal scenarios was 0% both at normocapnic and hypercapnic conditions. Yet routine metabolic rates (RMRs) were significantly affected by temperature, pH and embryonic stage. Immediately after hatching, the Fulton condition of juvenile bamboo sharks was significantly different in individuals that experienced future warming and hypercapnia; 30 days after hatching, survival rapidly declined in individuals experiencing both ocean warming and acidification (up to 44%). The RMR of juvenile sharks was also significantly affected by temperature and pH. The impact of low pH on ventilation rates was significant only under the higher thermal scenario. This study highlights the need of experimental-based risk assessments of sharks to climate change. In other words, it is critical to directly assess risk and vulnerability of sharks to ocean acidification and warming, and such effort can ultimately help managers and policy-makers to take proactive measures targeting most endangered species.

Sediment loads have long been known to be deleterious to corals, but the effects of turbidity and settling particles have not previously been partitioned. This study provides a novel approach using inert silicon carbide powder to partition and quantify the mechanical effects of sediment settling versus reduced light under a chronically high sedimentary regime on two turbid water corals commonly found in Singapore (Galaxea fascicularis and Goniopora somaliensis). Coral fragments were evenly distributed among three treatments: an open control (30% ambient PAR), a shaded control (15% ambient PAR) and sediment treatment (15% ambient PAR; 26.4 mg cm−2 day−1). The rate of photosynthesis and respiration, and the dark-adapted quantum yield were measured once a week for four weeks. By week four, the photosynthesis to respiration ratio (P/R ratio) and the photosynthetic yield (Fv/Fm) had fallen by 14% and 3–17% respectively in the shaded control, contrasting with corals exposed to sediments whose P/R ratio and yield had declined by 21% and 18–34% respectively. The differences in rates between the shaded control and the sediment treatment were attributed to the mechanical effects of sediment deposition. The physiological response to sediment stress differed between species with G. fascicularis experiencing a greater decline in the net photosynthetic yield (13%) than G. somaliensis (9.5%), but a smaller increase in the respiration rates (G. fascicularis = 9.9%, G. somaliensis = 14.2%). These different physiological responses were attributed, in part, to coral morphology and highlighted key physiological processes that drive species distribution along high to low turbidity and depositional gradients.

Animal metabolic rate is variable and may be affected by endogenous and exogenous factors, but such relationships remain poorly understood in many primitive fishes, including members of the family Acipenseridae (sturgeons). Using juvenile lake sturgeon (Acipenser fulvescens), the objective of this study was to test four hypotheses: 1) A. fulvescens exhibits a circadian rhythm influencing metabolic rate and behaviour; 2) A. fulvescens has the capacity to regulate metabolic rate when exposed to environmental hypoxia; 3) measurements of forced maximum metabolic rate (MMRF) are repeatable in individual fish; and 4) MMRF correlates positively with spontaneous maximum metabolic rate (MMRS). Metabolic rates were measured using intermittent flow respirometry, and a standard chase protocol was employed to elicit MMRF. Trials lasting 24 h were used to measure standard metabolic rate (SMR) and MMRS. Repeatability and correlations between MMRF and MMRS were analyzed using residual body mass corrected values. Results revealed that A. fulvescens exhibit a circadian rhythm in metabolic rate, with metabolism peaking at dawn. SMR was unaffected by hypoxia (30% air saturation (O2sat)), demonstrating oxygen regulation. In contrast, MMRF was affected by hypoxia and decreased across the range from 100% O2sat to 70% O2sat. MMRF was repeatable in individual fish, and MMRF correlated positively with MMRS, but the relationships between MMRF and MMRS were only revealed in fish exposed to hypoxia or 24 h constant light (i.e. environmental stressor). Our study provides evidence that the physiology of A. fulvescens is influenced by a circadian rhythm and suggests that A. fulvescens is an oxygen regulator, like most teleost fish. Finally, metabolic repeatability and positive correlations between MMRF and MMRS support the conjecture that MMRF represents a measure of organism performance that could be a target of natural selection.

To date, relatively few studies have tried to determine the practicality of using physiological information to help answer complex ecological questions and assist in conservation actions aimed at improving conditions for fish populations. In this study, the physiological stress responses of fish were evaluated in-stream between agricultural and forested stream reaches to determine whether differences in these responses can be used as tools to evaluate conservation actions. Creek chub Semotilus atromaculatus sampled directly from forested and agricultural stream segments did not show differences in a suite of physiological indicators. When given a thermal challenge in the laboratory, creek chub sampled from cooler forested stream reaches had higher cortisol levels and higher metabolic stress responses to thermal challenge than creek chub collected from warmer and more thermally variable agricultural reaches within the same stream. Despite fish from agricultural and forested stream segments having different primary and secondary stress responses, fish were able to maintain homeostasis of other physiological indicators to thermal challenge. These results demonstrate that local habitat conditions within discrete stream reaches may impact the stress responses of resident fish and provide insight into changes in community structure and the ability of tolerant fish species to persist in agricultural areas.

P. clarkii juvenile crayfish were exposed during 60 days to sublethal concentrations of glyphosate (G), polyoxyehtylene amine (P) or a combination of both (G+P), together with a control group of aged tap water (C). At the end of the experiment, the following statistical differences were noted, with respect to control: 1) a lower metabolic rate in both G and G+P groups, 2) a higher glycemia in G group with no differences in hemolymphatic lactate levels, 3) a lower muscle glycogen levels in both P and G+P groups, 4) a lower level of protein muscle in the P group. Taken together, these results suggest that glyphosate may cause a metabolic arrest. Additionally, under chronic exposure conditions, polyoxyehtylene amine acts as a strong stressor, leading to the utilization of both muscle carbohydrate and protein reserves.

Wave-driven water flow is a major force structuring marine communities. Species distributions are partly determined by the ability to cope with variation in water flow, such as differences in the assemblage of fish species found in a given water flow environment being linked to swimming ability (based on fin shape and mode of locomotion). It remains unclear, however, whether similar assembly rules apply within a species. Here we show phenotypic variation among sites in traits functionally linked to swimming ability in the damselfish Acanthochromis polyacanthus. These sites differ in wave energy and the observed patterns of phenotypic differences within A. polyacanthus closely mirrored those seen at the interspecific level. Fish from high-exposure sites had more tapered fins and higher maximum metabolic rates than conspecifics from sheltered sites. This translates to a 36 % larger aerobic scope and 33 % faster critical swimming speed for fish from exposed sites. Our results suggest that functional relationships among swimming phenotypes and water flow not only structure species assemblages, but can also shape patterns of phenotypic divergence within species. Close links between locomotor phenotype and local water flow conditions appear to be important for species distributions as well as phenotypic divergence across environmental gradients.

This study focused on the acute physiological responses to saltwater exposure in juvenile shortnose sturgeon Acipenser brevirostrum. In two separate laboratory experiments, 2 year‐old A. brevirostrum were exposed to either full (32) or half‐strength (16) seawater for up to 24 h. First, oxygen consumption rates were used to estimate the metabolic costs over 24 h. Secondly, blood and muscle samples were analysed at 6, 12 and 24 h for water loss, various measures of osmoregulatory status (plasma osmolality and ions) and other standard haematological variables. Juveniles exposed to full‐strength seawater showed significant decreases in oxygen consumption rates during the 24 h exposure. Furthermore, seawater‐exposed fish had significantly increased plasma osmolality, ions (Na + and Cl − ) and a 17% decrease in total wet mass over the 24 h exposure period. To a lesser extent, increases in osmolality, ions and mass loss were observed in fish exposed to half‐strength seawater but no changes to oxygen consumption. Cortisol was also significantly increased in fish exposed to full‐strength seawater. While plasma protein was elevated following 24 h in full‐strength seawater, haemoglobin, haematocrit and plasma glucose levels did not change with increased salinity. These results imply an inability of juvenile A. brevirostrum to regulate water and ions in full‐strength seawater within 24 h. Nonetheless, no mortality occurred in any exposure, suggesting that juvenile A. brevirostrum can tolerate short periods in saline environments.

The relationship between body mass ( M ) and metabolic rate was investigated through the assessment of active ( R A ) and standard ( R S ) metabolic rate at different life stages in zebrafish Danio rerio (5 day‐old larvae, 2 month‐old juveniles and 6 month‐old adults). Scaling exponents and constants were assessed for standard ( R S = 0·273 M 0·965 in mgO 2 g −1 h −1 ) and active metabolic rate ( R A = 0·799 M 0·926 in mgO 2 g −1 h −1 ). These data provide the basis for further experiments regarding the effects of environmental factors on aerobic metabolism throughout the life cycle of this species.

Cleaning symbioses play an important role in the health of certain coastal marine communities. These interspecific associations often occur at specific sites (cleaning stations) where a cleaner organism (commonly a fish or shrimp) removes ectoparasites/damaged tissue from a ‘client’ (a larger cooperating fish). At present, the potential impact of climate change on the fitness of cleaner organisms remains unknown. This study investigated the physiological and biochemical responses of tropical ( Lysmata amboinensis ) and temperate ( L. seticaudata ) cleaner shrimp to global warming. Specifically, thermal limits ( CTM ax), metabolic rates, thermal sensitivity, heat shock response ( HSR ), lipid peroxidation [malondialdehyde ( MDA ) concentration], lactate levels, antioxidant ( GST, SOD and catalase) and digestive enzyme activities (trypsin and alkaline phosphatase) at current and warming (+3 °C) temperature conditions. In contrast to the temperate species, CTM ax values decreased significantly from current (24–27 °C) to warming temperature conditions (30 °C) for the tropical shrimp, where metabolic thermal sensitivity was affected and the HSR was significantly reduced. MDA levels in tropical shrimp increased dramatically, indicating extreme cellular lipid peroxidation, which was not observed in the temperate shrimp. Lactate levels, GST and SOD activities were significantly enhanced within the muscle tissue of the tropical species. Digestive enzyme activities in the hepatopancreas of both species were significantly decreased by warmer temperatures. Our data suggest that the tropical cleaner shrimp will be more vulnerable to global warming than the temperate Lysmata seticaudata; the latter evolved in a relatively unstable environment with seasonal thermal variations that may have conferred greater adaptive plasticity. Thus, tropical cleaning symbioses may be challenged at a greater degree by warming‐related anthropogenic forcing, with potential cascading effects on the health and structuring of tropical coastal communities (e.g. coral reefs).

Molting is a stressful event in insect development. When an insect molts, the individual discards its exoskeleton and sheds and renews the interior lining of substantial portions of the respiratory (tracheal) system. We profiled for the first time the disruptive pattern of respiration during the molting process in larvae of the mayfly Cloeon dipterum (Ephemeroptera:Baetidae). Molting induces a precipitous drop in O2 consumption immediately followed by a surge in O2 consumption that appears to be compensatory in nature. Postmolt metabolic suppression is consistently observed during which O2 consumption rates lag relative to those of nonmolting larvae. Furthermore, the magnitude of respiratory disturbance during the molt increases as a function of temperature. Increasing temperatures increase molting frequency and the apparently stressful nature of the molt itself. Thus, the insect molt appears to be a previously unappreciated route by which warming conditions may affect aquatic insects.

Behavioural responses to changing environments affect community composition, so the identification of associations between environmental gradients, behavioural traits and physiological traits makes a significant contribution to the quest for trait‐based rules of community change. We tested the hypothesis that fish morphology and lifestyle are associated with metabolic rate, hence oxygen demand, and behavioural response to gradual hypoxia [low dissolved oxygen ( DO )], using respirometry and behavioural experiments. Three species fell along different points of the fast–slow lifestyle continuum: M elanotaenia fluviatilis, a pelagic fish adapted to endurance swimming, lies at the fast end of the lifestyle continuum, while M ogurnda adspersa, a benthic fish adapted to burst swimming, lies at the other end. The benthopelagic H ypseleotris sp. has an intermediate lifestyle. Standard and routine metabolic rates varied strongly among the species and were associated with lifestyle according to the inequality M. fluviatilis > H ypseleotris > M. adspersa. As DO declined, aquatic surface respiration behaviour also varied significantly among the species and indicated a sensitivity to hypoxia described by the same inequality. As hypoxia ensued, changes in habitat were also linked to lifestyle, but changes in activity level among species were not neatly correlated with lifestyle. Overall, our experiments imply that there are significant links between morphology, lifestyle, metabolism and behavioural response to hypoxia in these three species of fish.

This study examined the effects of acclimation temperature (10, 15, 20, or 25 °C) and an acute exposure to various temperatures on the routine metabolism of juvenile (~11 g) shortnose sturgeon (Acipenser brevirostrum). For the acclimation experiment, the minimum, mean, and maximum routine metabolic rates were established for sturgeon at each temperature. Mean routine metabolic rates for 10, 15, 20, and 25 °C were 134, 277, 313, and 309 mg O2 kg−1 h−1, respectively, with significant differences occurring between 10 and 15, 10 and 20, and 10 and 25 °C. For the acute exposure, similar patterns and significant differences were observed. Temperature quotient (Q 10) values indicate that the greatest effect of temperature occurred between 10 and 15 °C for both the acclimation and acute temperature experiments. In addition, the effect of temperature on the metabolic rate of sturgeon was nearly negligible between 15 and 25 °C. These results suggest that juvenile shortnose sturgeon are sensitive to temperature changes at the lower end of the range, and less sensitive in the mid-to-upper temperature range.

Growth requires that energy is directed towards ingestion, digestion, absorption and assimilation of a meal; energy expenditures are often expressed as the specific dynamic action (SDA). While SDA is an important part of fish energy budgets and strongly affected by water temperature, temperature effects are not known across a wide temperature range in Atlantic cod Gadus morhua. The objective of this study was to examine effects of temperature (2, 5, 10, 15 or 20 °C) on the energetic cost and time used for SDA in juvenile G. morhua by intermittent flow respirometry. At each temperature, G. morhua were fed a meal of herring (Clupea harengus) corresponding to 5 % of the body mass. Standard metabolic rates measured pre-feeding and post-feeding metabolic rates were measured to determine SDA. The study showed that SDA coefficients (%, SDA energy divided by meal energy) were significantly lower at 2 and 10 °C (5.4–6.3 %) compared to 5, 15 and 20 °C (10.4–12.4 %), while SDA duration increased significantly from 80 h at 10 °C to 130–160 h at 2, 15 and 20 °C and reached a maximum of 250 h at 5 °C. The significant decrease in SDA duration at 10 °C combined with a low SDA coefficient suggests that water temperatures close to 10 °C may represent the optimum temperatures for SDA in this population of G. morhua. Our results suggest that SDA is not a simple function of temperature, but may vary with temperature in a more complex fashion.

The increase of anthropogenic activities on coastal areas induces discharges of polycyclic aromatic hydrocarbons (PAHs) in aquatic ecosystem. PAH effects depend not only on their concentration and the way of contamination but also on the different developmental stages of the organism. Zebrafish were exposed to relevant concentration of pyrolytic PAHs from the first meal (i.e., 5-day post fertilization, dpf) to mature adults. Parental effect of this type of exposure was evaluated through the assessment of aerobic metabolic scope, cardiac frequency, and cardiac mRNA expression on larval and/or embryo progeny of contaminated fish. Our results suggest that cardiac frequency increased in larval descendants of fish exposed to the environmental concentration of pyrolytic PAHs (i.e., 5 ng.g−1 of food), while a lack of effect on aerobic metabolism in 5 dpf larvae was highlighted. A surexpression of mRNA related to the cardiac calcium transporting ATPase atp2a2a, a protein essential for contraction, is in accordance with this increasing cardiac frequency. Even if cardiac development genes cmlc1 and tnnt2a were not affected at early life stages tested, complementary work on cardiac structure could be interesting to better understand PAHs action.