Published papers

Chronic hypoxia exposure of fish can cause remodelling of the gills as well as increases to haematocrit and haemoglobin binding affinity. There is less known, however, about how chronic hypoxia affects the structure and function of the heart. In the current study, zebrafish were exposed to moderate hypoxia for 7 weeks and then ultrasound was used to characterize cardiac function. We found that cardiac output of the hypoxia-acclimated fish was greater than that of the control fish during an acute hypoxia exposure. This difference was due, at least in part, to the higher cardiac stroke volume. Histological measurements demonstrated an increase in the cross-sectional area of the ventricle of hypoxia-exposed fish and this was supported by higher end diastolic area measurements made using ultrasound. These changes to the heart occurred in conjunction with an increase in haematocrit and the respiratory surface area of the gills, as well as an improved capacity of the fish to respond to a more severe acute hypoxia challenge. We also found an increase in the expression of the gene transcripts for hif-1αa and vegfaa at 24 h, 3 days and 8 days of hypoxia exposure, suggesting a rapid and consistent response. Our results suggest that, unlike normoxia-acclimated fish which demonstrate a decrease in cardiac output with acute hypoxia exposure, zebrafish acclimated to hypoxia maintain cardiac output when acutely exposed to hypoxia.

Aeration is important for wastewater treatment. A significant amount of energy is used for the aeration process, sometimes up to 80 % of the total energy used at the wastewater treatment plant. Small sub-micrometer gas bubbles (“nanobubbles”) have been suggested as an alternative method for full or supplementary aeration to ensure an efficient process. This study investigates the aeration efficiency of a membrane-based nanobubble generator. The aim is to understand the role of nanobubbles in enhancing the aeration transfer efficiency, and to investigate whether nanobubbles can act as an oxygen reservoir, releasing oxygen into the liquid phase when the concentration falls below saturation. Data confirmed that the nanobubble generator enhances aeration efficiency compared with conventional methods. The gas content within the generated nanobubbles was examined, revealing negligible gas content within the nanobubbles themselves. These results suggest that the observed increase in the standard oxygen transfer efficiency (SOTE) was primarily attributable to the turbulence of liquid flow at the membrane surface and to the rapid transfer of oxygen from the formed bubbles to the liquid, rather than to significant oxygen storage in the nanobubbles themselves. The SOTE of clean water increased with the liquid flow rate and was 20 % at a flow rate of 10 L/min and 54 % at 20 L/min. Aeration happened quickly and the nanobubbles did not release a significant amount of oxygen after the generation process.

Quaternary ammonium compounds (QACs) such as benzalkonium compounds (BACs) are heavily used as biocides and are thus present in raw wastewater. BACs with dodecyl-, tetradecyl-, and hexadecyl groups as well as didecyl-dimethylammonium chloride (DDAC-10) were detected in all tested WWTPs with concentrations of 1728-3318; 1072-1830; 40-68 and 117-168 ng/L for DDAC-10, BAC-12, BAC-14 and BAC-16, respectively, dissolved in wastewater influent. The concentrations in the particulate phase of the wastewater were 20,000-300,000 times higher. Removals in the tested WWTPs exceeded 99%. Sorption constants to secondary and primary sludge (pK D ’s) ranged from 0.32 to 6.3. The biodegradation half-lives for DDAC-10, BAC-12, BAC-14, and BAC-16 were 31, 49, 13, and 68 h, respectively, even though they are strongly sorbing to sludge. Nine metabolites of BAC-12 were identified in the sludge incubation experiments, and five in the WWTP effluents, confirming the relevance of the biodegradation of QACs. Overall, the removal (from the water phase) is controlled by quick sorption, while the overall fate of QACs is controlled by biodegradation, as QACs are cycled in the WWTPs together with the sludge.

Our results indicate that regular exposure to challenging natural conditions activates mechanisms involved in hypoxia resistance in Aplysia californica. This experience is passed to the next generation, fading in the absence of exposure for at least two generations. Gene expression and physiological responses varied significantly between resistant and sensitive sea hares under normoxic and hypoxic conditions, displaying clear evidence of preconditioning in core hypoxia response pathways like HIF.

Despite extensive research in the last two decades, exploring the potential mechanisms underlying the sensitivity and resistance of marine organisms to ocean acidification is still imperative. Species interactions can play a role in these mechanisms, but the extent to which they modulate organismal responses to ocean acidification remains largely unknown. Here, we investigated how ocean acidification (pH 7.7) affects energy homeostasis and fitness of mussels (Mytilus coruscus) by assessing their physiological responses, intestinal microbiome and nutritional quality of their food (microalgae). Under ocean acidification, the mussels had reduced feeding rates by 34 % and reduced activities of digestive enzymes (pepsin by 39 %, trypsin by 28 % and lipase by 53 %) due to direct exposure to acidified seawater and increased phenol content of microalgae. Richness and diversity of intestinal microbiome (OTU, Chao1 index and Shannon index) were also lowered by ocean acidification, which can undermine nutrient absorption. On the other hand, energy expenditure of mussels increased by 53 % under ocean acidification, which was associated with the upregulation of antioxidant defence (SOD, CAT and GPx activities). Consequently, energy reserves in mussels decreased by 28 %, which were underpinned by the reduction in protein, carbohydrate and lipid contents. Overall, we demonstrate that ocean acidification could disrupt herbivore-algae and host-microbe interactions, thereby lowering the energy balance and impairing the health of marine organisms. This can have ramifications on the population and energy dynamics of marine communities in the acidifying ocean.

Bioavailable nitrogen governs ocean productivity and carbon fixation by regulating phytoplankton growth and community composition. Nitrogen input primarily results from fixation, while denitrification and anammox remove bioavailable nitrogen in oxygen‐depleted conditions. Traditionally considered limited to highly suboxic (i.e., <5 μM) waters, recent studies suggest that fixed‐nitrogen removal processes may extend beyond, elevating global nitrogen loss estimates. This study directly quantifies fixed‐nitrogen loss across oxygen gradients (from 140 to 32 μM) along the Estuary and Gulf of St. Lawrence using N cycle tracers (,, and ). Notably, we observe significant production when ambient concentrations fall below a threshold value of 58.9 ± 1.1 μM, including potential water column fixed‐nitrogen removal processes above suboxia. We hypothesis that ambient deoxygenation eases the formation of suboxic microareas in suspended organic matter. Benthic production remains unaffected under intensifying water column deoxygenation from 50 down to 32 μM, but the contribution of produced through nitrification in the sediment to denitrification diminishes as deoxygenation intensifies. Combined, water column and benthic fixed‐nitrogen removal processes drive anomalies and strong deficiency in bottom waters. Additionally, the observed threshold also triggers production. Overall, our study highlights the profound impact of coastal ocean deoxygenation on nitrogen cycling, suggesting unexpected shifts even at ambient oxygen concentrations traditionally considered well above suboxic conditions. This study explores processes that influence the availability of nitrogen, a limiting key nutrient for algal production and the biological carbon pump in the ocean. It focusses on nitrogen loss mechanisms which remove bioavailable nitrogen under barely detectable oxygen levels. Contrary to previous assumptions limiting these mechanisms to very low oxygen levels, this research suggests, in natural conditions, that nitrogen loss mechanisms can potentially occur in environments with higher ambient oxygen levels, challenging our understanding of nitrogen cycling. This study uses multiple nitrogen cycle tracers coupled with sediment core incubations to quantify nitrogen loss in the Estuary and Gulf of St. Lawrence. The findings include substantial bioavailable nitrogen loss and nitrous oxide production in the hypoxic water column as well as strong nitrate deficiency. This nitrogen loss can have broad implications and impact the growth and productivity of algae at the ocean surface. These insights will help to better predict the role of the ocean in the context of climate change. Key Points Fixed‐N is possibly removed in suboxic (<5 μM) microzones on suspended organic matter at bulk of 32–59 μM in the St. Lawrence Estuary Benthic and possibly water column fixed‐N removal processes drive a strong deficiency in bottom waters of the St. Lawrence Estuary Significant net production of was observed in bottom waters of the St. Lawrence Estuary when ambient fell below 59 μM

Forecasts indicate that rising temperatures towards the future and the expansion of dead zones will change environmental suitability for fish early stages. Therefore, we assessed the chronic effects of warming (26 °C), hypoxia (<2-2.5 mg L -1 ) or their combination on mortality rate, growth, behaviour, energy metabolism and oxidative stress using Atherina presbyter larvae as a model species. There were no differences between the treatments in terms of mortality rate. The combination of warming and hypoxia induced faster loss of body mass (+22.7%). Warming, hypoxia or their combination enhanced boldness (+14.7-25.4%), but decreased exploration (-95%-121%), increased the time in frozen state (+60.6-80.5%) and depleted swimming speed (-45.6-50.5%). Moreover, routine metabolic rate was depleted under hypoxia or under the combination of warming and hypoxia (-56.6 and 57.2%, respectively). Under hypoxia, increased catalase activity (+56.3%) indicates some level of antioxidant defence capacity, although increased DNA damage (+25.2%) has also been observed. Larvae also exhibited a great capacity to maintain the anaerobic metabolism stable in all situations, but the aerobic metabolism is enhanced (+19.3%) when exposed to the combination of both stressors. The integrative approach showed that changes in most target responses can be explained physiologically by oxidative stress responses. Increased oxidative damages (lipid peroxidation and DNA damage) and increased interaction between antioxidant enzymes (superoxide dismutase and catalase) are associated to increased time in frozen state and decreased swimming activity, growth rates and boldness. Under all stressful situations, larvae reduced energy-consuming behaviours (e.g. depleted exploration and swimming activity) likely to stabilize or compensate for the aerobic and anaerobic metabolisms. Despite being an active small pelagic fish, we concluded that the sensitive larval phase exhibited complex coping strategies to physiologically acclimate under thermal and hypoxic stress via behavioural responses.

Red drum, Sciaenops ocellatus, are a marine teleost native to the Gulf of Mexico that routinely experiences periods of low oxygen (hypoxia). Recent work has demonstrated this species has the capacity to improve aerobic performance in hypoxia through respiratory acclimation. However, it remains unknown how hypoxia acclimation impacts anaerobic metabolism in red drum, and the consequences of exhaustive exercise and recovery. Juvenile fish were acclimated to normoxia (n = 15, DO 90.4 ± 6.42 %) or hypoxia (n = 15, DO 33.6 ± 7.2 %) for 8 days then sampled at three time points: at rest, after exercise, and after a 3 h recovery period. The resting time point was used to characterize the acclimated phenotype, while the remaining time points demonstrate how this phenotype responds to exhaustive exercise. Whole blood, red muscle, white muscle, and heart tissues were sampled for metabolites and enzyme activity. The resting phenotype was characterized by lower pH e and changes to skeletal muscle ATP. Exhaustive exercise increased muscle lactate, and decreased phosphocreatine and ATP with no effect of acclimation. Interestingly, hypoxia-acclimated fish had higher pH e and pH i than control in all exercise time points. Red muscle ATP was lower in hypoxia-acclimated fish versus control at each sample period. Moreover, acclimated fish increased lactate dehydrogenase activity in the red muscle. Hypoxia acclimation increased white muscle ATP and hexokinase activity, a glycolytic enzyme. In a gait-transition swim test, hypoxia-acclimated fish recruited anaerobic-powered burst swimming at lower speeds in normoxia compared to control fish. These data suggest that acclimation increases reliance on anaerobic metabolism, and does not benefit recovery from exhaustive exercise.

Nano-titanium dioxide (nano-TiO2) is a ubiquitous contaminant in the marine environment that accumulates in sediments and biological tissues. Coupled with global warming, these challenges can enhance the deleterious properties of nano-TiO2, leading to compounded pollution effects on marine life and ecosystems. This study investigated the effects of nano-TiO2 and increased temperatures on the Japanese swimming crab's gut microbiota and digestive system, Charybdis japonica, through different scenarios. We employed three exposure scenarios: direct exposure (DE) of the crabs to warming and nano-TiO2, indirect exposure (IE) through consumption of mussels Mytilus coruscus subjected to the same conditions, and combined exposure (CE), where crabs were directly exposed to warming and nano-TiO2 while consuming affected mussels. Additionally, a control group was established, comprising Japanese crab C. japonica and thick-shelled mussel M. coruscus that were reared under standard temperature (22 °C, the average annual temperature in the region where the mussels and crabs were sampled) and 0 mg L−1 nano-TiO2 concentration conditions. The findings indicated that warming and nano-TiO2 disrupted the crabs' ATP production, digestive responses, and body chemical composition, leading to intestinal flora dysfunction. Notably, nano-TiO2 exerted a stronger impact on the crabs' digestive enzymes and intestinal flora than warming alone; however, the concurrent presence of warming and nano-TiO2, especially under the direct exposure (DE) conditions, generally exacerbated the negative effects of nano-TiO2. This research provides valuable insights into the implications of nano-TiO2 and elevated temperature on the digestive responses of marine crabs.

Coastal marine environments are characterized by daily, seasonal and long-term changes in both O2 and CO2, driven by local biotic and abiotic factors. The neuroepithelial cells (NECs) of fish are thought to be the putative chemoreceptors for sensing oxygen and CO2, and, thus, NECs play a key role in detecting these environmental changes. However, the role of NECs as chemosensors in marine fish remains largely understudied. In this study, the NECs of marine threespine sticklebacks (Gasterosteus aculeatus) were characterized using immunohistochemistry. We then determined if there were changes in NEC size and density, and in gill morphology in response to either mild (10 kPa) or moderate (6.8 kPa) hypoxia and two levels of elevated CO2 (1,500 and 3,000 µatm). We found that the NECs of stickleback contained synaptic vesicles and were innervated, and were 50–300% larger and 2 to 4 times more abundant than in other similar sized freshwater fishes. NEC size and density were largely unaffected by exposure to hypoxia, but there was a 50% decrease in interlamellar cell mass (ILCM) in response to mild and moderate hypoxia. NECs increased in size, but not abundance in response to elevated CO2. Moreover, fish exposed to moderate or elevated CO2 had 53–78% larger ILCMs compared to control fish. Our results demonstrated that adult marine sticklebacks have NECs that can respond to environmentally relevant pCO2 and likely hypoxia, which highlights the importance of NECs in marine fishes under the heterogeneity of environmental conditions in coastal areas.

Assessing how at-risk species respond to co-occurring stressors is critical for predicting climate change vulnerability. In this study, we characterized how young-of-the-year White Sturgeon (Acipenser transmontanus) cope with warming and low oxygen (hypoxia) and investigated whether prior exposure to one stressor may improve the tolerance to a subsequent stressor through “cross-tolerance”. Fish were acclimated to five temperatures within their natural range (14-22°C) for one month prior to assessment of thermal tolerance (critical thermal maxima, CTmax) and hypoxia tolerance (incipient lethal oxygen saturation, ILOS; tested at 20°C). White Sturgeon showed a high capacity for thermal acclimation, linearly increasing thermal tolerance with increasing acclimation temperature (slope = 0.55, adjusted R2 = 0.79), and an overall acclimation response ratio (ARR) of 0.58, from 14°C (CTmax = 29.4 ± 0.2°C, mean ± S.E.M.) to 22°C (CTmax = 34.1 ± 0.2°C). Acute warming most negatively impacted hypoxia tolerance in 14°C-acclimated fish (ILOS = 15.79 ± 0.74% air saturation), but prior acclimation to 20°C conferred the greatest hypoxia tolerance at this temperature (ILOS = 2.60 ± 1.74% air saturation). Interestingly, individuals that had been previously tested for thermal tolerance had lower hypoxia tolerance than naïve fish that had no prior testing. This was particularly apparent for hypoxia-tolerant 20°C-acclimated fish, whereas naïve fish persisted the entire 15-h duration of the hypoxia trial and did not lose equilibrium at air saturation levels below 20%. Warm-acclimated fish demonstrated significantly smaller relative ventricular mass, indicating potential changes to tissue oxygen delivery, but no other changes to red blood cell characteristics and somatic indices. These data suggest young-of-the-year White Sturgeon are resilient to warming and hypoxia, but the order in which these stressors are experienced and whether exposures are acute or chronic may have important effects on phenotype.

Juvenile sea bass were relatively successful in keeping acid base balance under an ocean acidification scenario. However, this came at a cost for ionoregulation with reduced NKA, NKCC and Rhbg expression rates as a consequence.

Reef fishes in the California Current Ecosystem have evolved in habitats affected by seasonally variable, episodic upwelling of high pCO2 (acidified, low pH) and low dissolved oxygen (deoxygenated) water, which suggests that these fishes might exhibit resilience to ocean acidification (OA) and deoxygenation. Yet, how the fitness of these fish are affected by natural variability in pH and DO over short time scales remains poorly understood, as do the effects of longer-term trends in pH and DO driven by climate change. We conducted a complementary suite of experiments to study the effects of acidification and deoxygenation on the critical swimming speed (Ucrit) of juvenile copper (Sebastes caurinus) and black (S. melanops) rockfish collected from nearshore habitats in an ocean acidification “hotspot” off Northern California. We consistently observed that Ucrit declined more strongly in response to deoxygenation than to acidification, at least under ranges of these stressors consistent with current conditions and plausible future scenarios, and that reduction in swimming performance reflected additive rather than synergistic responses to concurrent exposure. Reductions in swimming performance manifested quickly–on the scale of hours–in response to exposure to elevated pCO2/reduced DO, yet are reversible: swimming performance of juvenile rockfish recovers within a matter of days, and perhaps much more quickly, after acidified/deoxygenated conditions have subsided. Insights from this study address potential effects of variability in upwelling intensity at event and seasonal scales for nearshore rockfishes and contribute to our understanding of fish responses to future ocean conditions driven by ongoing climate change.

In this study, Atlantic salmon were: (i) implanted with heart rate (fH) data storage tags (DSTs), pharmacologically stimulated to maximum fH, and warmed at 10°C h−1 (i.e. tested using a ‘rapid screening protocol’); (ii) fitted with Doppler® flow probes, recovered in respirometers and given a critical thermal maximum (CTmax) test at 2°C h−1; and (iii) implanted with fH DSTs, recovered in a tank with conspecifics for 4 weeks, and had their CTmax determined at 2°C h−1. Fish in respirometers and those free-swimming were also exposed to a stepwise decrease in water oxygen level (100% to 30% air saturation) to determine the oxygen level at which bradycardia occurred. Resting fH was much lower in free-swimming fish than in those in respirometers (∼49 versus 69 beats min−1) and this was reflected in their scope for fH (∼104 versus 71 beats min−1) and CTmax (27.7 versus 25.9°C). Further, the Arrhenius breakpoint temperature and temperature at peak fH for free-swimming fish were considerably greater than for those tested in the respirometers and given a rapid screening protocol (18.4, 18.1 and 14.6°C; and 26.5, 23.2 and 20.2°C, respectively). Finally, the oxygen level at which bradycardia occurred was significantly higher in free-swimming salmon than in those in respirometers (∼62% versus 53% air saturation). These results: highlight the limitations of some lab-based methods of determining fH parameters and thermal tolerance in fishes; and suggest that scope for fH may be a more reliable and predictive measure of a fish's upper thermal tolerance than their peak fH.

Predicted climate change-induced increases in heat waves and hypoxic events will have profound effects on fishes, yet the capacity of parents to alter offspring phenotype via non-genetic inheritance and buffer against these combined stressors is not clear. This study tested how prolonged adult zebrafish exposure to combined diel cycles of thermal stress and hypoxia affect offspring early survival and development, parental investment of cortisol and heat shock proteins (HSPs), larval offspring stress responses, and both parental and offspring heat and hypoxia tolerance. Parental exposure to the combined stressor did not affect fecundity, but increased mortality, produced smaller embryos and delayed hatching. The combined treatment also reduced maternal deposition of cortisol and increased embryo hsf1, hsp70a, HSP70, hsp90aa and HSP90 levels. In larvae, basal cortisol levels did not differ between treatments, but acute exposure to combined heat stress and hypoxia increased cortisol levels in control larvae with no effect on larvae from exposed parents. In contrast, whereas larval basal hsf1, hsp70a and hsp90aa levels differed between parental treatments, the combined acute stressor elicited similar transcriptional responses across treatments. Moreover, the combined acute stressor only induced a marked increase in HSP47 levels in the larvae derived from exposed parents. Finally, combined hypoxia and elevated temperatures increased both thermal and hypoxia tolerance in adults and conferred an increase in offspring thermal but not hypoxia tolerance. These results demonstrate that intergenerational acclimation to combined thermal stress and hypoxia elicit complex carryover effects on stress responsiveness and offspring tolerance with potential consequences for resilience.

Although stress exposure is typically detrimental, here, we highlight protective interactions where exposure to mild stress can increase an organism's resilience to a different stressor – a phenomenon termed ‘cross-protection’.

Providing optimal conditions for early-life gas bladder inflation of captive fish is one of the biggest challenges in fish culture. It also applies to laboratory fishes. Turquoise killifish (Nothobranchius furzeri Jubb, 1971) is a popular research model in biogerontology due to its short lifespan. Annual killifish in laboratory culture frequently suffer from an inability to inflate their gas bladder which may stem from suboptimal environmental conditions in captivity. Here, we investigate (1) the effect of dissolved oxygen (DO) saturation and (2) access to the water surface on gas bladder inflation and hatching success of turquoise killifish. We further histologically examine the gas bladder development from its primordial form to full inflation. In accordance with physoclistous nature of turquoise killifish, access to the water surface is not necessary for gas bladder inflation. We found that hatching success was highest in the treatment with constant or decreasing DO saturation. In contrast, the highest proportion of larvae with inflated gas bladders was found in the treatment with DO oversaturated water (130%) which was induced by the addition of an oxygen tablet. Larvae inflated their gas bladders within 2 to 48 h post-hatching. These findings represent a major step toward a solution to a persistent problem in laboratory culture of this increasingly important model organism.

Variations in dissolved oxygen levels are common in the Amazonian aquatic environments and the aquatic organisms that inhabit these environments developed a variety of adaptive responses to deal with such conditions. Some Amazonian fish species are tolerant to low oxygen levels and the cichlid Astronotus ocellatus is one of the most hypoxia-tolerant species. Herein, we aimed to unveil the biochemical and molecular responses that A. ocellatus presents when submitted to hypoxia. Hypoxia indicators were measured, such as plasma glucose, plasma lactate, hepatic glycogen and relative transcript levels of prolyl hydroxylase 2 (phd2) and hypoxia-inducible factor-1α (hif-1α) in juveniles of approximately 50 g exposed to 1, 3, and 5 hours of hypoxia (0.7 mg O2.L-1), followed by 3 hours of recovery in normoxia (6 mg O2.L-1). Fish exposed to hypoxia reduced liver glycogen levels within 3 hours of hypoxia, when comparing with 1 hour, and increased plasma glucose and lactate. Under the same condition, phd2 transcripts levels increased in gills, but decreased in liver. In contrast, hypoxia did not affect relative gene expression of hif-1α in both tissues. Based on the transcription pattern of phd2, these results showed that liver and gills of A. ocellatus have different molecular strategies to cope with environmental hypoxia.

Aquatic ecosystems are globally significant sources of the greenhouse gas methane to the atmosphere. Until recently, methane production was thought to be a strictly anaerobic process confined primarily to anoxic sediments. However, supersaturation of methane in oxygenated waters has been consistently observed in lakes and the ocean (termed the ‘methane paradox’), indicating that methane can be produced under oxic conditions through unclear mechanisms. Here we show aerobic methane production from multiple sources in freshwater incubation experiments under different treatments and based on biogeochemical, metagenomic, and metatranscriptomic data. We find that aerobic methane production appears to be associated with (bacterio)chlorophyll metabolism and photosynthesis, as well as with Proteobacterial degradation of methylphosphonate. Genes encoding pathways for putative photosynthetic- and methylphosphonate-based methane production also co-occur in Proteobacterial metagenome-assembled genomes. Our findings provide insight into known mechanisms of aerobic methane production, and suggest a potential co-occurring mechanism associated with bacterial photosynthesis in aquatic ecosystems. The mechanisms underlying methane production in oxygenated waters of oceans and lakes are unclear. Here, Perez-Coronel and Beman show that aerobic methane production in freshwater incubation experiments is associated with (bacterio)chlorophyll metabolism and photosynthesis, and with Proteobacterial degradation of methylphosphonate.

Oceanic oxygen minimum zones (OMZs) are globally significant sites of biogeochemical cycling where microorganisms deplete dissolved oxygen (DO) to concentrations <20 µM. Amid intense competition for DO in these metabolically challenging environments, aerobic nitrite oxidation may consume significant amounts of DO and help maintain low DO concentrations, but this remains unquantified. Using parallel measurements of oxygen consumption rates and 15N-nitrite oxidation rates applied to both water column profiles and oxygen manipulation experiments, we show that the contribution of nitrite oxidation to overall DO consumption systematically increases as DO declines below 2 µM. Nitrite oxidation can account for all DO consumption only under DO concentrations <393 nM found in and below the secondary chlorophyll maximum. These patterns are consistent across sampling stations and experiments, reflecting coupling between nitrate reduction and nitrite-oxidizing Nitrospina with high oxygen affinity (based on isotopic and omic data). Collectively our results demonstrate that nitrite oxidation plays a pivotal role in the maintenance and biogeochemical dynamics of OMZs. Oxygen is fundamental for marine life, yet it is absent from large areas of the ocean. Here the authors demonstrate that microbial nitrite oxidation effectively consumes oxygen where oxygen concentrations are low, playing a pivotal role in these regions.

The impacts of warming temperatures associated with climate change on performance are poorly understood in most mammals. Thermal performance curves are a valuable means of examining the effects of temperature on performance traits, but they have rarely been used in endotherms. Here, we examined the thermal performance curve of endurance running capacity at high temperatures in the deer mouse (Peromyscus maniculatus). Endurance capacity was measured using an incremental speed test on a treadmill, and subcutaneous temperature in the abdominal region was measured as a proxy for body temperature (Tb). Endurance time at 20°C was repeatable but varied appreciably across individuals, and was unaffected by sex or body mass. Endurance capacity was maintained across a broad range of ambient temperatures (Ta) but was reduced above 35°C. Tb during running varied with Ta, and reductions in endurance were associated with Tb greater than 40°C when Ta was above 35°C. At the high Ta that limited endurance running capacity (but not at lower Ta), Tb tended to rise throughout running trials with increases in running speed. Metabolic and thermoregulatory measurements at rest showed that Tb, evaporative water loss and breathing frequency increased at Ta of 36°C and above. Therefore, the upper threshold temperatures at which endurance capacity is impaired are similar to those inducing heat responses at rest in this species. These findings help discern the mechanisms by which deer mice are impacted by warming temperatures, and provide a general approach for examining thermal breadth of performance in small mammals.

Physiological and environmental stressors can cause osmotic stress in fish hearts, leading to a reduction in intracellular taurine concentration. Taurine is a β-amino acid known to regulate cardiac function in other animal models but its role in fish has not been well characterized. We generated a model of cardiac taurine deficiency (TD) by feeding brook char (Salvelinus fontinalis) a diet enriched in β-alanine, which inhibits cardiomyocyte taurine uptake. Cardiac taurine levels were reduced by 21% and stress-induced changes in normal taurine handling were observed in TD brook char. Responses to exhaustive exercise and acute thermal and hypoxia tolerance were then assessed using a combination of in vivo, in vitro and biochemical approaches. Critical thermal maximum was higher in TD brook char despite significant reductions in maximum heart rate. In vivo, TD brook char exhibited a lower resting heart rate, blunted hypoxic bradycardia and a severe reduction in time to loss of equilibrium under hypoxia. In vitro function was similar between control and TD hearts under oxygenated conditions, but stroke volume and cardiac output were severely compromised in TD hearts under severe hypoxia. Aspects of mitochondrial structure and function were also impacted in TD permeabilized cardiomyocytes, but overall effects were modest. High levels of intracellular taurine are required to achieve maximum cardiac function in brook char and cardiac taurine efflux may be necessary to support heart function under stress. Taurine appears to play a vital, previously unrecognized role in supporting cardiovascular function and stress tolerance in fish.

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.

Thermal tolerance is crucial to understanding the biology of fishes and their responses to changes in temperatures, such as that produced by climate change. Shortnose sturgeon (Acipenser brevirostrum) is an endangered species (USA) and a species of special concern (Canada) that live on the eastern coast of North America. Although previous studies have focused on the acute critical thermal maximum (CTmax) of shortnose sturgeon, nothing is known with respect to their acute critical thermal minimum (CTmin) and the overall thermal tolerance of this species. This study examined the upper (CTmax) and lower (CTmin) thermal tolerance of shortnose sturgeon acclimated to 12 and 18°C. CTmax increased with increasing acclimation temperature; however, there was no significant relationship between acclimation temperature and CTmin. Taken together, the results of the present study show that shortnose sturgeon are well adapted to tolerate acute exposures to both cold and warm water environments.

Climate change and anthropological activities have led to an expansion of hypoxia into the natural habitat of Cancer irroratus. In this study, we examined the effects of hypoxia and food deprivation state on food intake and subsequent gastric processing. Three different techniques were used to measure food intake. The gravimetric analysis of dry food pellets was the most accurate method. In severe hypoxia (20% oxygen), rock crabs reduced food intake, and more crabs refused to eat. Compared with fasted crabs, more starved crabs tended to eat in severe hypoxia. Subsequently, prolonged gastric emptying times paralleled the previously measured postprandial oxygen consumption in hypoxia. Starved crabs also exhibited slightly longer transit times for digesta compared with fasted crabs. These results suggest that although a trade-off may occur in starved rock crabs between the need to procure nutrients and deal with hypoxic stress, impaired digestive processing may still deleteriously affect these animals.

There is a scientific debate whether oxygen concentration may be a factor driving the pattern of size decrease at higher temperature. Central to this debate is the fact that oxygen availability relative to demand for living organisms decreases with increasing temperature. We examined whether rotifers Lecane inermis exposed to hypoxic conditions would evolve smaller sizes than rotifers exposed to normoxic conditions, using experimental evolution with the same fluctuating temperature but differentiated by three regimes of oxygen availability: normoxia, hypoxia throughout the whole thermal range, and hypoxia only at the highest temperature. Immediately after the six-month experiment (more than 90 generations), we tested the plasticity of size responses to temperature in three post-evolution groups, and we related these responses to fitness. The results show that normoxic rotifers had evolved significantly larger sizes than two hypoxic rotifer groups, which were similar in size. All three groups displayed similar plastic body size reductions in response to warming over the range of temperatures they were exposed to during the period of experimental evolution, but they showed different and complex responses at two temperatures below this range. Any type of plastic response to different temperatures resulted in a similar fitness pattern across post-evolution groups. We conclude that (i) these rotifers showed a genetic basis for the pattern of size decrease following evolution under both temperature-dependent and temperature-independent hypoxia; and (ii) plastic body size responds consistently to temperatures that are within the thermal range that the rotifers experienced during their evolutionary history, but responses become more noisy at novel temperatures, suggesting the importance of evolutionary responses to reliable environmental cues.

After being exposed to environmental stimuli during early developmental stages, some organisms may gain or weaken physiological regulating abilities, which would have long-lasting effects on their performance. Environmental hypoxia events can have significant effects on marine organisms, but for breeding programs and other practical applications, it is important to further explore the long-term physiological effects of early hypoxia exposure in economically significant species. In this study, the Pacific abalone Haliotis discus hannai was exposed to moderate hypoxia (∼4 mg/L) from zygote to trochophora, and the assessments of hypoxia tolerance were conducted on the grow-out stage. The results revealed that juvenile abalones exposed to hypoxia at the early development stages were more hypoxia-tolerant but with slower weight growth, a phenomenon called the trade-off between growth and survival. These phenotypic effects driven by the hypoxia exposure were explained by strong selection of genes involved in signal transduction, autophagy, apoptosis, and hormone regulation. Moreover, long non-coding RNA regulation plays an important role modulating carry-over effects by controlling DNA replication and repair, signal transduction, myocardial activity, and hormone regulation. This study revealed that the ability to create favorable phenotypic differentiation through genetic selection and/or epigenetic regulation is important for the survival and development of aquatic animals in the face of rapidly changing environmental conditions.

The Alaska blackfish ( Dallia pectoralis ) is a facultative air-breather endemic to northern latitudes where it remains active in winter under ice cover in cold hypoxic waters. To understand the changes in cellular Ca 2+ cycling that allow the heart to function in cold hypoxic water, we acclimated Alaska blackfish to cold (5 °C) normoxia or cold hypoxia (2.1-4.2 kPa; no air access) for 5-8 weeks. We then assessed the impact of the acclimation conditions on intracellular Ca 2+ transients (Δ[Ca 2+ ] i ) of isolated ventricular myocytes and contractile performance of isometrically-contracting ventricular strips. Measurements were obtained at various contractile frequencies (0.2-0.6 Hz) in normoxia, during acute exposure to hypoxia, and reoxygenation at 5 °C. The results show that hypoxia-acclimated Alaska blackfish compensate against the depressive effects of hypoxia on excitation-contraction coupling by remodelling cellular Δ[Ca 2+ ] i to maintain ventricular contractility. When measured at 0.2 Hz in normoxia, hypoxia-acclimated ventricular myocytes had a 3.8-fold larger Δ[Ca 2+ ] i peak amplitude with a 4.1-fold faster rate of rise, compared to normoxia-acclimated ventricular myocytes. At the tissue level, maximal developed force was 2.1-fold greater in preparations from hypoxia-acclimated animals. However, maximal attainable contraction frequencies in hypoxia were lower in hypoxia-acclimated myocytes and strips than preparations from normoxic animals. Moreover, the inability of hypoxia-acclimated ventricular myocytes and strips to contract at high frequency persisted upon reoxygenation. Overall, the findings indicate that hypoxia alters aspects of Alaska blackfish cardiac myocyte Ca 2+ cycling, and that there may be consequences for heart rate elevation during hypoxia, which may impact cardiac output in vivo.

The Alaska blackfish (Dallia pectoralis) is the only air-breathing fish in the Arctic. In the summer, a modified esophagus allows the fish to extract oxygen from the air, but this behavior is not possible in the winter because of ice and snow cover. The lack of oxygen (hypoxia) and near freezing temperatures in winter is expected to severely compromise metabolism, and yet remarkably, overwintering Alaska blackfish remain active. To maintain energy balance in the brain and limit the accumulation of reactive oxygen species (ROS), we hypothesized that cold hypoxic conditions would trigger brain mitochondrial remodeling in the Alaska blackfish. To address this hypothesis, fish were acclimated to warm (15 °C) normoxia, cold (5 °C) normoxia or cold hypoxia (5 °C, 2.1–4.2 kPa; no air access) for 5–8 weeks. Mitochondrial respiration, ADP affinity and H 2 0 2 production were measured at 10 °C in isolated brain homogenates with an Oroboros respirometer. Cold acclimation and chronic hypoxia had no effects on mitochondrial aerobic capacity or ADP affinity. However, cold acclimation in normoxia led to a suppression of brain mitochondrial H 2 0 2 production, which persisted and became more pronounced in the cold hypoxic fish. Overall, our study suggests cold acclimation supresses ROS production in Alaska blackfish, which may protect the fish from oxidative stress when oxygen becomes limited during winter.

Multiple lines of evidence suggest that an inability of the ventricle to contract in coordination with the pacemaker during anoxia exposure may suppress cardiac pumping rate in anoxia-tolerant turtles. To determine under what extracellular conditions the ventricle could be the weak link that limits cardiac pumping, we compared, under various extracellular conditions, the intrinsic contractile properties of isometrically-contracting ventricular and atrial strips obtained from 21 °C- to 5 °C- acclimated turtles ( Trachemys scripta ) that had been exposed to either normoxia or anoxia (16 h at 21 °C; 12 days at 5 °C). We found that combined extracellular anoxia, acidosis, and hyperkalemia (AAK), severely disrupted ventricular, but not right or left atrial, excitability and contractibility of 5 °C anoxic turtles. However, combined hypercalcemia and heightened adrenergic stimulation counteracted the negative effects of AAK. We also report that the turtle heart is resilient to prolonged diastolic intervals, which would ensure that contractile force is maintained if arrhythmia were to occur during anoxia exposure. Finally, our findings reinforce that prior temperature and anoxia experiences are central to the intrinsic contractile response of the turtle myocardium to altered extracellular conditions. At 21 °C, prior anoxia exposure preconditioned the ventricle for anoxic and acidosis exposure. At 5 °C, prior anoxia exposure evoked heightened sensitivity of the ventricle to hyperkalemia, as well as all chambers to combined hypercalcemia and increased adrenergic stimulation. Overall, our findings show that the ventricle could limit cardiac pumping rate during prolonged anoxic submergence in cold-acclimated turtles if hypercalcemia and heightened adrenergic stimulation are insufficient to counteract the negative effects of combined extracellular anoxia, acidosis, and hyperkalemia.

Goldfish enter a hypometabolic state to survive chronic hypoxia. We recently described tissue-specific contributions of membrane lipid composition remodeling and mitochondrial function to metabolic suppression across different goldfish tissues. However, the molecular and especially epigenetic foundations of hypoxia tolerance in goldfish under metabolic suppression are not well understood. Here we show that components of the molecular oxygen-sensing machinery are robustly activated across tissues irrespective of hypoxia duration. Induction of gene expression of enzymes involved in DNA methylation turnover and microRNA biogenesis suggest a role for epigenetic transcriptional and post-transcriptional suppression of gene expression in the hypoxia-acclimated brain. Conversely, mechanistic target of rapamycin-dependent translational machinery activity is not reduced in liver and white muscle, suggesting this pathway does not contribute to lowering cellular energy expenditure. Finally, molecular evidence supports previously reported chronic hypoxia-dependent changes in membrane cholesterol, lipid metabolism and mitochondrial function via changes in transcripts involved in cholesterol biosynthesis, β-oxidation, and mitochondrial fusion in multiple tissues. Overall, this study shows that chronic hypoxia robustly induces expression of oxygen-sensing machinery across tissues, induces repressive transcriptional and post-transcriptional epigenetic marks especially in the chronic hypoxia-acclimated brain and supports a role for membrane remodeling and mitochondrial function and dynamics in promoting metabolic suppression.

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

Climate change has emerged as an increasingly important threat to freshwater systems. To cope with rapidly changing thermal regimes, freshwater fishes must either relocate or adjust through genetic adaptation and/or phenotypic plasticity. Short‐term responses to elevated water temperature have been well studied in freshwater fishes; however, far less is understood about change induced by long‐term exposure. Furthermore, few studies have investigated the effects of temperature on already imperilled species, which may be more sensitive to environmental change. This study investigated the effects of rearing temperature on critical thermal maximum (CT max ), agitation temperature ( T ag, temperature at which fish show behavioural signs of thermal stress) and gill size in pugnose shiner, Notropis anogenus, a threatened species in Canada. Juvenile pugnose shiner were reared for 4 months across five different ecologically relevant temperatures. CT max and T ag were measured under normoxia and acute exposure to hypoxia to test for oxygen sensitivity of the upper thermal limits in this species. CT max increased with elevated water temperature. T ag also increased with rearing temperature and occurred, on average, 4.3°C above acclimation temperatures. The CT max and T ag were lower when fish were exposed acutely to hypoxia. Interestingly, gill size (e.g. total gill filament length) increased with rearing temperature, which may increase oxygen uptake capacity and support increased metabolic demands of warmer waters. Overall, pugnose shiner show plasticity in several traits in response to long‐term exposure to elevated water temperature that may facilitate persistence in warmer waters. However, acute hypoxia exposure reduced thermal tolerance, stressing the importance of evaluating interactive effects of multiple stressors. Identifying source populations of pugnose shiner with greater thermal tolerance or implementing captive breeding under higher temperature regimes may improve the success of re‐introduction efforts in the face of climate change, but the consequences to fitness of increased thermal tolerance should be examined.

Globally, kelp forests are threatened by multiple stressors, including increasing grazing by sea urchins. With coastal upwelling predicted to increase in intensity and duration in the future, understanding whether kelp forest and urchin barren urchins are differentially affected by upwelling-related stressors will give insight into how future conditions may affect the transition between kelp forests and barrens. We assessed how current and future-predicted changes in the duration and magnitude of upwelling-associated stressors (low pH, dissolved oxygen, and temperature) affected the performance of purple sea urchins (Strongylocentrotus purpuratus) sourced from rapidly-declining bull kelp (Nereocystis leutkeana) forests and nearby barrens and maintained on habitat-specific diets. Kelp forest urchins were of superior condition to barrens urchins, with ~ 6–9 times more gonad per body mass. Grazing and condition in kelp forest urchins were more negatively affected by distant-future and extreme upwelling conditions, whereas grazing and survival in urchins from barrens were sensitive to both current-day and all future-predicted upwelling, and to increases in acidity, hypoxia, and temperature regardless of upwelling. We conclude that urchin barren urchins are more susceptible to increases in the magnitude and duration of upwelling-related stressors than kelp forest urchins. These findings have important implications for urchin population dynamics and their interaction with kelp.

Proper development of the O2-sensing system is essential for survival. Here, we characterized the development of the O2-sensing system in the mangrove rivulus (Kryptolebias marmoratus), an amphibious fish that transitions between hypoxic aquatic environments and O2-rich terrestrial environments. We found that NECs formed in the gills and skin of K. marmoratus during embryonic development and that both NEC populations are retained from the embryonic stage to adulthood. We also found that the hyperventilatory response to acute hypoxia was present in embryonic K. marmoratus, indicating that functional O2-sensing pathways are formed during embryonic development. We then exposed embryos to aquatic normoxia, aquatic hyperoxia, aquatic hypoxia, or terrestrial conditions for the first 30 days of embryonic development and tested the hypothesis that environmental O2 availability during embryonic development modulates the development of the O2-sensing system in amphibious fishes. Surprisingly, we found that O2 availability during embryonic development had little impact on the density and morphology of NECs in the gills and skin of K. marmoratus. Collectively, our results demonstrate that, unlike the only other species of fish in which NEC development has been studied to date (i.e., zebrafish), NEC development in K. marmoratus is largely unaffected by environmental O2 levels during the embryonic stage, indicating that there is interspecies variation in O2-induced plasticity in the O2-sensing system of fishes.

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.

Ecosystem feedbacks in response to ocean acidification can amplify or diminish the diel pH oscillations that characterize productive coastal waters. We report that benthic microalgae generate such oscillations in the porewater of cohesive sediment and ask how carbonation (acidification) of the overlying seawater alters these in the absence and presence of biogenic calcite. To do so, we placed a 1-mm layer of ground oyster shells (Treatment) or sand (Control) onto intact sediment cores free of large dwelling fauna, and then gradually increased the p CO 2 in the seawater above half of the Treatment and Control cores from 472 to 1216 μatm (pH 8.0 to 7.6, CO 2:HCO 3 - from 4.8 to 9.6 x 10 -4 ). Vertical porewater [O 2 ] and [H + ] microprofiles measured 16 d later showed that this carbonation had decreased O 2 penetration in all cores, indicating a metabolic response. In carbonated seawater: (1) sediment biogeochemical processes added and removed more H + to and from the porewater in darkness and light, respectively, than in ambient seawater increasing the amplitude of the dark–light porewater [H + ] oscillations, and (2) the dissolution of calcite decreased the porewater [H + ] below that in overlying seawater, reversing the dark sediment–seawater H + flux and decreasing the amplitude of diel [H + ] oscillations. This dissolution did not, however, counter the negative effect of carbonation on sediment O 2 penetration. We hypothesise that the latter effect and the observed enhanced acidification of the sediment porewater were caused by an ecosystem feedback: a CO 2 -induced increase in the microbial reoxidation of reduced solutes with O 2.

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.

Studies of heart function and metabolism have been used to predict the impact of global warming on fish survival and distribution, and their susceptibility to acute and chronic temperature increases. Yet, despite the fact that hypoxia and high temperatures often co-occur, only one study has examined the effects of hypoxia on fish thermal tolerance, and the consequences of hypoxia for fish cardiac responses to acute warming have not been investigated. We report that sablefish ( Anoplopoma fimbria ) did not increase heart rate or cardiac output when warmed while hypoxic, and that this response was associated with reductions in maximum O 2 consumption and thermal tolerance (CT max ) of 66% and approximately 3°C, respectively. Further, acclimation to hypoxia for four to six months did not substantially alter the sablefish's temperature-dependent physiological responses or improve its CT max. These results provide novel, and compelling, evidence that hypoxia can impair the cardiac and metabolic response to increased temperatures in fish, and suggest that some coastal species may be more vulnerable to climate change-related heat waves than previously thought. Further, they support research showing that cross-tolerance and physiological plasticity in fish following hypoxia acclimation are limited.

This study investigated the combined effects of seawater acidification and hypoxia on the gonadal antioxidant response of the thick shell mussel Mytilus coruscus mainly distributed along the Shengsi Island, East China Sea, where hypoxia and pH fluctuations frequently occur in summer. Mussels were exposed to three pH levels (8.1, 7.7 and 7.3) and two dissolved oxygen (DO) levels (6 and 2 mg L − 1 ) for 21 days following a 10-day recovery. Activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione (GSH), glutathione S-transferase (GST) and malondialdehyde (MDA) in gonad and gonad surface area (GSA) were measured at day 21 and 31. Among all the parameters, there was no significant change in SOD activity. GSA and the activity of CAT and GST were decreased under acidification and hypoxia, but GPX, GSH and MDA were increased. PCA showed that the changes were influenced by pH more than DO. Interaction between acidification and hypoxia was found significant on GPX activity and GSA. Integrated biomarker response (IBR) analysis demonstrated that acidification and hypoxia impaired mussel’s antioxidant system and increased oxidative damage. Our results clearly showed that acidification and hypoxia synergistically exert negative impact on the antioxidant system and gonad development of mussels, and the effect of acidification was more significant.

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.

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.

This work shows that the combination of anoxia and inhibition of GABA receptors induces seizure-like activities in goldfish telencephalic pyramidal and stellate neurons. Importantly, to prevent seizure-like activity, an intact GABA-mediated inhibitory pathway is required.

Consistent individual differences in behaviour, known as animal personalities, have been demonstrated within and across species. In fish, studies applying an animal personality approach have been used to resolve variation in physiological and molecular data suggesting a linkage, genotype-phenotype, between behaviour and transcriptome regulation. In this study, using three fish species (zebrafish; Danio rerio, Atlantic salmon; Salmo salar and European sea bass; Dicentrarchus labrax), we firstly address whether personality-specific mRNA transcript abundances are transferrable across distantly-related fish species and secondly whether a proactive transcriptome signature is conserved across all three species. Previous zebrafish transcriptome data was used as a foundation to produce a curated list of mRNA transcripts related to animal personality across all three species. mRNA transcript copy numbers for selected gene targets show that differential mRNA transcript abundance in the brain appears to be partially conserved across species relative to personality type. Secondly, we performed RNA-Seq using whole brains from S. salar and D. labrax scoring positively for both behavioural and molecular assays for proactive behaviour. We further enriched this dataset by incorporating a zebrafish brain transcriptome dataset specific to the proactive phenotype. Our results indicate that cross-species molecular signatures related to proactive behaviour are functionally conserved where shared functional pathways suggest that evolutionary convergence may be more important than individual mRNAs. Our data supports the proposition that highly polygenic clusters of genes, with small additive effects, likely support the underpinning molecular variation related to the animal personalities in the fish used in this study. The polygenic nature of the proactive brain transcriptome across all three species questions the existence of specific molecular signatures for proactive behaviour, at least at the granularity of specific regulatory gene modules, level of genes, gene networks and molecular functions.

Increasing inputs of organic matter (OM) are driving declining dissolved oxygen (DO) concentrations in coastal ecosystems worldwide. The quantity, source, and composition of OM transported to coastal ecosystems via stormwater runoff have been altered by land use changes associated with urbanization and subsequent hydrologic flows that accompany urban stormwater management. To elucidate the role of stormwater in the decline of coastal DO, rain event sampling of biochemical oxygen demand (BOD) in samples collected from the outfall of stormwater ponds and wetlands, as well as samples of largely untreated runoff carried by stormwater ditches, was conducted across a range of urban and suburban development densities. Sampling also included measurements of particulate and dissolved carbon and nitrogen, carbon and nitrogen stable isotopes, and chlorophyll- a. Results suggest stormwater may be a significant source of labile OM to receiving waters, especially during the first flush of runoff, even though BOD concentrations vary both among and within sites in response to rain events. BOD variability was best predicted by particulate OM (POM) and chlorophyll- a, rather than the larger pool of dissolved OM. These findings demonstrate the importance of managing episodic stormwater discharge, especially POM, from urbanized areas to mitigate DO impairment in larger downstream systems.

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.

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.

Oceanic oxygen minimum zones (OMZs) play a pivotal role in biogeochemical cycles due to extensive microbial activity. How OMZ microbial communities assemble and respond to environmental variation is therefore essential to understanding OMZ functioning and ocean biogeochemistry. Sampling along depth profiles at five stations in the eastern tropical North Pacific Ocean (ETNP), we captured systematic variations in dissolved oxygen (DO) and associated variables (nitrite, chlorophyll, ammonium) with depth and between stations. We quantitatively analyzed relationships between oceanographic gradients and microbial community assembly and activity based on paired 16S rDNA and 16S rRNA sequencing. Overall microbial community composition and diversity were strongly related to regional variations in density, DO, and other variables (regression and redundancy analysis r2 =0.68-0.82), displaying predictable patterns with depth and between stations. Although similar factors influenced the active community, diversity was substantially lower within the OMZ. We also identified multiple active microbiological networks that tracked specific gradients or features-particularly subsurface ammonium and nitrite maxima. Our findings indicate that overall microbial community assembly is consistently shaped by hydrography and biogeochemistry, while active segments of the community form discrete networks inhabiting distinct portions of the water column, and that both are tightly tuned to environmental conditions in the ETNP. This article is protected by copyright. All rights reserved.

To facilitate conservation planning, there is a need for improved confidence in forecasts of climate change impacts on species distributions. Towards that end, there have been calls for the development of process‐based models to test hypotheses concerning the mechanisms by which temperature shapes distribution and to corroborate forecasts of correlative models. Models of temperature‐dependent growth (TDG) were developed for two Australian riverine blackfishes with disjunct longitudinal distributions: Gadopsis marmoratus (occupies lower, warmer elevations) and Gadopsis bispinosus (occupies higher, cooler elevations). The models were used to (a) predict blackfish monthly and annual growth dynamics under current and future climate scenarios within different elevation bands of their current distribution, and (b) test the hypothesis that, under the current climate, the distributions of each species would be positively correlated with predicted TDG. Increases in mean annual growth were forecast for both species under all warming scenarios, across all elevation bands. Both species currently occupy annual habitat temperatures below those optimal for growth. Under certain warming scenarios, the predicted increases in annual growth belie forecasts of within‐year dynamics that may interact with the phenology of blackfish to impair recruitment. There was not a significant positive linear relationship between predicted TDG and observed abundance among river segments for either species. Both species were strongly under‐represented where annual growth rates were forecast to be optimal and over‐represented where growth rates were forecast to be intermediate. Confidence in forecasts of climate change impacts based on correlative models will increase when those forecasts are consistent with a mechanistic understanding of how specific drivers (e.g. water temperature) affect processes (e.g. growth). This process‐based study revealed surprises concerning how future climates may affect fish growth dynamics, showing that although the blackfish distributions are correlated with temperature the temperature‐dependent mechanisms underpinning that correlation require further investigation.

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.

The morphology of fish gills is closely linked to aerobic capacity and tolerance of environmental stressors such as hypoxia. The importance of gill surface area is well studied, but little is known about how the mechanical properties of gill tissues determine function. In some fishes, the bases of the gill filaments are surrounded by a calcified ‘sheath' of unknown function. We tested two non-exclusive hypotheses: (i) calcified gill filaments enhance water flow through the gill basket, improving aquatic respiratory function, and (ii) in amphibious fishes, calcification provides support for gills out of water. In a survey of more than 100 species of killifishes and related orders, we found filament calcification was widespread and thus probably arose before the evolution of amphibious lifestyles in killifishes. Calcification also did not differ between amphibious and fully aquatic species, but terrestrial acclimation caused calcium deposition on the filaments of the killifish Kryptolebias marmoratus, suggesting a possible structural role when out of water. We found strong evidence supporting a role for filament calcification in enhancing aquatic respiratory function. First, acclimation to increased respiratory demands (hypoxia, elevated temperatures) induced calcium deposition on the filaments of K. marmoratus. Next, gentle removal of filament calcification decreased branchial resistance to water flow, indicating disruption of gill basket positioning. Thus, the mechanical properties of the gill filaments appear to play an important and previously unappreciated role in determining fish respiratory function.

Catfish Ictalurus spp. are subjected to stressful conditions during harvest, which may be linked to fillet coloration and quality. Poor water quality in ponds, socks or hauling tanks, as well as handling stress, have been suggested to cause red fillets in catfish; however, chronic exposure has not resulted in red fillets. Short‐term occurrences of extreme poor water quality, particularly low dissolved oxygen, high carbon dioxide and high temperature, may occur in ponds or during harvest. Therefore, market‐sized Channel Catfish Ictalurus punctatus were acutely exposed (12 hr) to one of the three water quality treatments while confined during a simulated socking procedure and evaluated for stress responses by means of change in blood parameters and fillet quality. In fish subjected to the extreme treatment, hematocrit, plasma cortisol, glucose and lactate levels increased, with 22% mortality, indicating highly stressful conditions. In fish subjected to moderate and typical (control) treatments, cortisol increased but a lack of change or decrease in glucose and lactate indicated minimal anaerobic metabolism. Only one red fillet was produced by the extreme treatment and two by the typical treatment; therefore, the results suggest red fillets are not a product of poor water quality compounded by handling during harvest.

Ocean acidification has become serious, and seawater hypoxia has become evident in acidified waters. The combination of such stressors may have interactive effects on the fitness of marine organisms. In order to investigate the interactive effects of seawater acidification and hypoxia on the early development of marine bivalves, the eggs and sperm of the thick shell mussel Mytilus coruscus were exposed to combined treatments of pH (8.1, 7.7, 7.3) and dissolved oxygen (2, 6 mg/L) for 96 h culture observation to investigate the interactive effects of seawater acidification and hypoxia on the early development of marine bivalves. Results showed that acidification and hypoxia had significant negative effects on various parameters of the early development of the thick shell mussel. However, hypoxia had no effect on fertilization rate. Significant interactions between acidification and hypoxia were observed during the experiment. Short-term exposure negatively influenced the early development of the thick shell mussel but did not affect its survival. The effects of long-term exposure to these two environmental stresses need further study.

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.

Environmental hypoxia has effected numerous and well‐documented anatomical, physiological and behavioural adaptations in fishes. Comparatively little is known about hypoxia's impacts on sensing because it is difficult to quantify sensory acquisition in vivo. Weakly electric fishes, however, rely heavily on an easily‐measurable sensory modality—active electric sensing—whereby individuals emit and detect electric organ discharges (EODs). In this study, hypoxia tolerance of a mormyrid weakly electric fish, Marcusenius victoriae, was assessed by examining both its metabolic and EOD rates using a critical threshold ( p crit ) paradigm. The routine metabolic rate was 1.42 mg O 2 h −1, and the associated critical oxygen tension was 14.34 mmHg. Routine EOD rate was 5.68 Hz with an associated critical tension of 15.14 mmHg. These metabolic indicators of hypoxia tolerance measured in this study were consistent with those in previous studies on M. victoriae and other weakly electric fishes. Furthermore, our results suggest that some aerobic processes may be reduced in favour of maintaining the EOD rate under extreme hypoxia. These findings underscore the importance of the active electrosensory modality to these hypoxia‐tolerant fish.

Hypoxia, a frequent occurring threat in coastal regions, often results in mass mortalities of marine organisms and brings a serious ecological problem. The commercially important Zhikong scallop Chlamys farreri is being under such a threat as the risks of eutrophication and hypoxia have risen in their culture areas. However, little information has been known concerning their tolerance to hypoxia and their strategy for survival. In the present study, a 20-day experiment was conducted to determine the effects of hypoxia on the survival, behavior, and metabolism of Zhikong scallop. With the LC50 for dissolved oxygen (DO) being estimated as 1.8 mg/L, the survival of Zhikong scallop can be greatly challenged even under the moderate hypoxic condition of around 2.0 mg/L DO. The survival rate ranged from 69% to 59% when DO dropped from 3.0 to 2.0 mg/L, and it was further reduced to 47% at 1.5 mg/L DO. In hypoxic conditions, the scallops became significantly active, which may be explained as escape attempts to avoid hypoxic water. To save energy, Zhikong scallop would depress their respiration. However, when DO dropped from 3.0 to 2.0 mg/L, the oxygen consumption rate hardly changed. The upregulation of lactate dehydrogenase activity and the unrepressed phosphofructokinase activity, which often result in the unbalanced cellular homeostasis and energy budget, may account for the observed increase in the mortality rate of Zhikong scallops. In general, Zhikong scallop is sensitive to hypoxia events, though possible escape attempts, depressed respiration, and oxaloacetate-pathway may increase their survival chance.

Portable clinical analysers are gradually being involved in on-site assessment of haematic parameters in fish. The purpose of this study was to evaluate the i-STAT portable clinical analyser (i-STAT PCA) for accuracy and reliability of measuring blood pH, partial pressure of oxygen (pO2), haematocrit, haemoglobin, sodium, potassium and calcium in Atlantic cod (Gadus morhua). Haematological parameters detected with the i-STAT PCA were compared with conventional laboratory techniques (CLTs). Two types of disposable cartridges were used (CHEM8+ and CG4+) with the i-STAT PCA, and experiments were performed at two different temperature regimes (5 °C and 15 °C) and four different carbon dioxide (CO2) levels (0%, 0.1%, 0.5% and 1%). All blood parameters measured with the i-STAT PCA showed heterogeneous inaccuracy under the tested conditions, but the highest discrepancies were registered in blood pO2. The i-STAT PCA systematically overestimated the pO2 measurements. Our research suggests that i-STAT PCA is not an appropriate tool for pO2 measurements especially in coldwater fish species. The i-STAT PCA consistently underestimated the pH and haematocrit values especially at a lower temperature, although those parameters indicate significant high correlation at 15 °C. Furthermore, the analysed ions showed overestimation of sodium and underestimation of potassium and calcium.

Anthropogenic emission of atmospheric carbon dioxide (CO2) has led to a rapid increase in atmospheric CO2 concentration. Increasing atmospheric CO2 can reduce seawater pH and carbonate ions, which may adversely affect the survival of the larvae of calcareous animals. Cyclina sinensis is a commercially and ecologically important species in several Asian countries. Living in coast shallow waters, this species has experienced the coastal environmental changes frequently throughout its life cycle. In this study, we simulated possible future seawater pH values including 8.2, 7.8 and 7.4 and examined the effects of ocean acidification on the early development of C. sinensis. Clam embryos were incubated for 48 h (2 d) in control and high-CO2 seawater to compare embryogenesis, larval growth and swimming behavior. Fertilization rate was quite sensitive to pH, and moderate acidification could induce a significant decrease in fertilization rate. However, only extreme acidification could bring significant negative effect to hatching rate, body size, and average path velocity of trochophora. Moreover, with seawater acidification, C. sinensis needs much more time to reach the same developmental stage, which increases the risk of larva survival. Together with recent studies demonstrating negative impacts of high CO2 on fertilization and larva swimming behavior, the results imply a future decrease of C. sinensis populations in oceans if its acclimation to the predicted environmental alteration does not occur.

Stormwater retention ponds commonly receive some wastewater through misconnections, sewer leaks, and sewer overloads, all of which leads to unintended loads of organic micropollutants, including pharmaceuticals. This study explores the role of pond sediment in removing pharmaceuticals (naproxen, carbamazepine, sulfamethoxazole, furosemide, and fenofibrate). It quantifies their sorption potential to the sediments and how it depends on pH. Then it addresses the degradability of the pharmaceuticals in microcosms holding sediment beds and pond water. The sediment-water partitioning coefficient of fenofibrate varied little with pH and was the highest (average log Kd: 4.42 L kg−1). Sulfamethoxazole had the lowest (average log Kd: 0.80 L kg−1), varying unsystematically with pH. The coefficients of naproxen, furosemide and carbamazepine were in between. The degradation by the sediments was most pronounced for sulfamethoxazole, followed by naproxen, fenofibrate, furosemide, and carbamazepine. The first three were all removed from the water phase with half-life of 2–8 days. Over the 38 days the experiment lasted, they were all degraded to near completion. The latter two were more resistant, with half-lives between 1 and 2 months. Overall, the study indicated that stormwater retention ponds have the potential to remove some but not all pharmaceuticals contained in wastewater contributions.

Individuals in a fish population differ in key life-history traits such as growth rate and body size. This raises the question of whether such traits cluster along a fast-slow growth continuum according to a pace-of-life syndrome (POLS). Fish species like salmonids may develop a bimodal size distribution, providing an opportunity to study the relationships between individual growth and behavioural responsiveness. Here we test whether proactive characteristics (bold behaviour coupled with low post-stress cortisol production) are related to fast growth and developmental rate in Atlantic salmon, Salmo salar. Boldness was tested in a highly controlled two-tank hypoxia test were oxygen levels were gradually decreased in one of the tanks. All fish became inactive close to the bottom at 70% oxygen saturation. At 40% oxygen saturation level a fraction of the fish actively sought to avoid hypoxia. A proactive stress coping style was verified by lower cortisol response to a standardized stressor. Two distinct clusters of bimodal growth trajectories were identified, with fast growth and early smoltification in 80% of the total population. There was a higher frequency of proactive than reactive individuals in this fast-developing fraction of fish. The smolts were associated with higher post-stress plasma cortisol than parr, and the proactive smolts leaving hypoxia had significant lower post-stress cortisol than the stayers. The study demonstrated a link between a proactive coping and fast growth and developmental ratio and suggests that selection for domestic production traits promotes this trait cluster.

The Manila clam Ruditapes philippinarum has become a common and dominant macrobenthic species in coastal areas of the northwestern Pacific and temperate waters of Europe; it is also a major cultured shellfish, with annual worldwide production exceeding 3.3 million tonnes. This species faces greater risk of exposure to hypoxia as eutrophication worsens throughout its coastal habitats; however, its tolerance to hypoxia remains unclear, and the toxicological indicators including LC50 and LT50 have not yet been assessed. Previous studies on the effects of hypoxia on marine benthos have focused largely on functional responses, such as metabolism and gene expression, leaving potential structural damage to the mitochondria or the cells unknown. In this study we assessed the effects of hypoxia on Manila clam in terms of survival, behavior, metabolism and cellular damage, using a newly designed automated hypoxia simulation device that features exceptional accuracy and good stability. The clams exhibited strong tolerance to hypoxia as the 20-day LC50 for dissolved oxygen (DO) was estimated to be 0.57 mg L-1, and the LT50 at 0.5 mg L-1 DO was 422 hours. Adaptations included fewer buried clams and a depressed metabolism, while the unexpected rise in the activities of key enzymes involved in glycolysis may indicate a diverse strategy of shellfish under hypoxia. Cellular damage was observed as collapse of the mitochondrial cristae and both cellular and mitochondrial vacuolization. This multi-level study complements and updates our knowledge of the effects of hypoxia on marine benthos, by improving our understanding of the potential for marine ecological transformation under hypoxic conditions and providing useful information for Manila clam farming.

Chesapeake Bay is the primary nursery for striped bass ( Morone saxatilis ), which are increasingly being exposed to hypoxic waters. Tolerance to hypoxia in fish is generally determined by a single exposure of an isolated individual or by exposing large groups of conspecifics to hypoxia without regard to social status. The importance of social context in determining physiological responses to stressors is being increasingly recognized. To determine whether social interactions influence hypoxia tolerance (HT) in striped bass, loss of equilibrium HT was assessed in the same fish while manipulating the social environment around it. Small group settings were used to be more representative of the normal sociality experienced by this species than the paired encounters typically used. After establishing the dominance hierarchy within a group of fish, HT was determined collectively for the individuals in that group, and then new groups were constructed from the same pool of fish. Individuals could then be followed across multiple settings for both repeatability of HT and hierarchy position ( X ¯ = 4.2 ± 0.91 SD groups per individual). HT increased with repeated exposures to hypoxia ( P < 0.001 ), with a significant increase by a third exposure ( P = 0.004 ). Despite this changing HT, rank order of HT was significantly repeatable across trials for 6 mo ( P = 0.012 ). Social status was significantly repeatable across trials of different group composition ( P = 0.02 ) and unrelated to growth rate but affected HT weakly in a complex interaction with size. Final HT was significantly correlated with blood [hemoglobin] and hematocrit. The repeatability and large intraspecific variance of HT in juvenile striped bass suggest that HT is potentially an important determinant of Darwinian fitness in an increasingly hypoxic Chesapeake Bay.

Environmental stressors, such as warm temperatures and hypoxia, can interact and pose a threat to aquatic species. Cross talk between the hypoxia and heat stress cellular pathways can lead to enhanced cross tolerance between these environmental stressors. In this study, we questioned whether elevated temperatures (from 27° to 32°C) during rearing would enhance the hypoxia-inducible transcription factor-1 (HIF-1)-mediated transcriptional response to hypoxia (5% dissolved O 2 ) in early stages of zebrafish development and whether these differences would be associated with enhanced larval tolerance and survival to hypoxia. We found that embryos reared at 32°C had an enhanced cellular HIF-1 response (elevated hif-1ab and insulin-like growth factor binding-protein mRNA level) and that acute hypoxia (4 h) activated the heat-shock response (elevated hsp70a and hsp90aa mRNA levels). Elevated rearing temperatures and hypoxia exposure also induced precocious hatching, but neither environmental stressor had an effect on the hypoxia tolerance (critical O 2 tension) of 4-d-old larvae and did not protect larvae against the lethal effects of a second acute hypoxia exposure. Overall, during early zebrafish development, cross talk between the hypoxia and heat stress cellular pathways at the gene expression level did not confer cross tolerance at the whole-animal level with respect to hypoxia stress.

Hypoxia and climate warming are pervasive stressors in aquatic systems that may have interactive effects on fishes because both affect aerobic metabolism. We explored independent and interactive effects of dissolved oxygen (DO) and temperature on thermal tolerance, behavior, and fitness-related traits of juvenile F 1 offspring of the African cichlid Pseudocrenilabrus multicolor. Fish were reared in a split-brood design with four treatments (low or high DO, cool or hot temperature); thermal tolerance, growth, and condition were measured after 1 mo in the rearing treatments, following which behavioral traits were measured over 3.6 mo. Critical thermal maximum was higher in fish reared under hot conditions but was not affected by hypoxia. There was an interactive effect of DO and temperature on agitation temperature (temperature at which fish show behavioral signs of thermal stress) and the thermal agitation window (°C between the onset of agitation and final loss of equilibrium). Fish reared and tested under hot, normoxic conditions showed a higher agitation temperature, while fish reared and tested under hot, hypoxic conditions showed the largest thermal agitation window. Fish grew more quickly in length under hot than cool conditions and more quickly under normoxic than hypoxic conditions. Fish reared under cool, normoxic conditions were characterized by higher condition than other groups. Both cool and hypoxic rearing conditions reduced activity and aggression. These results highlight the importance of integrating physiological tolerance measures with sublethal behavioral effects of hypoxia and high temperature to gain a fuller understanding of species responses to multiple stressors.

Pacific hagfish, Eptatretus stoutii, can recover from 36 h of anoxia and their systemic hearts continue to work throughout the exposure. Recent work demonstrates that glycogen stores are utilized in the E. stoutii heart during anoxia but that these are not sufficient to support the measured rate of ATP production. One metabolic fuel that could supplement glycogen during anoxia is glycerol. This substrate can be derived from lipid stores, stored in the heart, or delivered via the blood. The purpose of this study was to determine the effect of glycerol on the contractile function of the excised E. stoutii heart during anoxia exposure. When excised hearts, perfused with metabolite free saline (mf-saline), were exposed to anoxia for 12 h, there was no difference in heart rate, pressure generation (max-dP), rate of contraction (max-dP/dtsys), or rate of relaxation (max-dP/dtdia) compared to hearts perfused with mf-saline in normoxia. However, hearts perfused with saline containing glycerol (gly-saline) in anoxia had higher max-dP, max-dP/dtsys, and max-dP/dtdia than hearts perfused with mf-saline in anoxia. Tissue levels of glycerol increased when hearts were perfused with gly-saline in normoxia, but not when perfused with gly-saline in anoxia. Anoxia exposure did not affect the activities of triglyceride lipase, glycerol kinase, or glycerol-3-phosphate dehydrogenase. This study suggests that glycerol stimulates cardiac function in the hagfish but that it is not derived from stored lipids. How glycerol may stimulate contraction is not known. This could be as an energy substrate, as an allosteric factor, or a combination of the two.

As poikilotherms, fish health is compromised by exposure to elevated temperatures (e.g. climate change-related warming, anthropogenic thermal pollution, and/or hatchery processes). While fish thermotolerance has been demonstrated to be plastic, the downstream impacts of early life-stage high temperature exposure are not known. In the present study, we investigated the thermotolerance of rainbow trout (Oncorhynchus mykiss) fry 2 months after being exposed to elevated temperature (22°C) for 96 h. Exposed fry demonstrated a reduced critical thermal maxima (CTmax) in comparison to control fish. Using the RNase H-dependent quantitative PCR method, expression of rainbow trout hsp70 isoforms was determined immediately after the acute thermal stress and immediately following the thermotolerance trials. The lowered CTmax was associated with a reduced ability to upregulate the hsp70b gene during the thermotolerance trials, whereas no changes in hsp70a were observed. Overall, these results indicate that exposure to thermal stress in early life-stages of rainbow trout can have negative effects on future physiological function.

Photosystem II (PSII) splits water and drives electron transfer to plastoquinone via photochemical reactions using light energy. It is surrounded by light‐harvesting complex II (LHCII) to form the PSII – LHCII supercomplex. Complete characterization of its structure and function has, however, been hampered due to instability of the complex in the presence of detergent. To overcome this problem, we developed a new procedure for purifying the PSII – LHCII supercomplexes of Chlamydomonas reinhardtii employing amphipol A8‐35. The obtained supercomplexes showed little LHCII dissociation even 4 days after purification. Oxygen‐evolving activity was retained within amphipol if the extrinsic polypeptides were kept associated by betaine. Electron microscopy revealed that this method also improved structural uniformity and that the major organization was C 2 S 2 M 2 L 2.

The herbicide bentazone is used extensively worldwide, and it is frequently detected in groundwater sources used for drinking water production. Previously, bentazone has been shown to be biodegraded in filter sand from biological rapid sand filters at various waterworks. This untapped potential could be an inexpensive and sustainable alternative for the removal of trace organic contaminants. To study the fate of bentazone in sand filters and to identify associated risks, degradation pathways in filter sand were identified and the toxicity of identified transformation products was evaluated using quantitative structure–activity relationship (QSAR) modelling. Bentazone degradation was investigated in microcosm experiments with filter sand, effluent water and bentazone at elevated (5 mg L−1) and environmentally relevant concentrations (<10 μg L−1). The investigations at elevated concentrations revealed up to 10 transformation products, suggesting three main biotransformation pathways: 1) oxidation of the isopropyl-moiety to the corresponding carboxylic acid, 2) oxidation of the aromatic ring leading to ring cleavage and subsequent decarboxylation reactions, and 3) N-methylation followed by oxidation to a carboxylic acid. At environmentally relevant concentrations, 92% of the initial bentazone was removed within 13 days, and at this point only one transformation product, carboxy-bentazone, could be detected in the water. QSAR-models considering both human and environmentally relevant endpoints showed that degradation in filter sand led to a detoxification of bentazone. Initial oxidation processes followed by further degradation, and partial mineralization highlights the relevance of both methanotrophs and heterotrophs for the bentazone degradation in rapid sand filters.

Hydrocarbons contamination and hypoxia are two stressors that can coexist in coastal ecosystems. At present, few studies evaluated the combined impact of these stressors on fish physiology and behavior. Here, we tested the effect of the combination of hypoxia and petrogenic hydrocarbons on the anti-predator locomotor performance of fish. Specifically, two groups of European sea bass (Dicentrarchus labrax) were exposed to clean water (Ctrl) or oil-contaminated water (Oil). Subsequently, fish of both groups were placed in normoxic (norx) or hypoxic (hyp) experimental tanks (i.e. four groups of fish were formed: Ctrl norx, Ctrl hyp, Oil norx, Oil hyp). In these tanks, escape response 2 was elicited by a mechano-acoustic stimulus and recorded with a high speed camera. Several variables were analyzed: escape response duration, responsiveness (percentage of fish responding to the stimulation), latency (time taken by the fish to initiate a response), directionality (defined as away or toward the stimulus), distance-time variables (such as speed and acceleration), maneuverability variables (such as turning rate), escape trajectory (angle of flight) and distancing of the fish from the stimulus. Results revealed (i) effects of stressors (Ctrl hyp, Oil norx and Oil hyp) on the directionality; (ii) effects of Oil norx and Oil hyp on maneuverability and (iii) effects of Oil hyp on distancing. These results suggest that individual stressors could alter the escape response of fish and that their combination could strengthen these effects. Such an impact could decrease the probability of prey escape success. By investigating the effects of hydrocarbons (and the interaction with hypoxia) on the anti-predator behavior of fish, this work increases our understanding of the biological impact of oil spill. Additionally, the results of this study are of interest for oil spill impact evaluation and also for developing new ecotoxicological tools of ecological significance.

The shortnose sturgeon (Acipenser brevirostrum Lesueur, 1818) is a species of special concern in Canada, but little is known about their thermal biology. Information on the upper thermal tolerance of shortnose sturgeon becomes valuable for predicting future survival particularly with climate change and improving species management. Using a modified critical thermal maximum (CTmax) methodology, the objective is to determine whether previous thermal stress affects the thermal tolerance of juvenile shortnose sturgeon when exposed to a second thermal stress event. Prior exposure to thermal stress (CTmax1) did not affect the thermal tolerance (CTmax2) of juvenile shortnose sturgeon when a 24 h recovery period was allotted between tests. However, a significant increase in thermal tolerance occurred when the recovery time between the two thermal challenges was 1 h. Plasma glucose, lactate, and osmolality were all significantly affected by thermal stress, but values returned to control levels within 24 h. Hematocrit and plasma chloride concentrations were not significantly affected by thermal stress. All fish survived the CTmax testing. The data indicate that the thermal tolerance of juvenile shortnose sturgeon is modified when multiple thermal stresses occur closer together (1 h) but not if separated by a longer time period (24 h).

Drinking water supply is in many parts of the world based on groundwater. Groundwater often contains methane, which can be oxidized by methanotrophs upon aeration. Sand from rapid sand filters fed with methane-rich groundwater can remove some pesticides (Hedegaard and Albrechtsen in Water Res 48:71-81, 2014). We enriched methanotrophs from filter sand and investigated whether they could drive the degradation of various pesticides. To enrich for methanotrophs, we designed and operated four laboratory-scale, continuously methane-fed column reactors, inoculated with filter sand and one control column fed with tap water. When enrichments were obtained, methane was continuously supplied to three reactors, while the fourth was starved for methane for 1 week, and the reactors were spiked with ten pesticides at groundwater-relevant concentrations (2.1-6.6 μg/L). Removal for most pesticides was not detected at the investigated contact time (1.37 min). However, the degradation of phenoxy acids was observed in the methanotrophic column reactor starved for methane, while it was not detected in the control column indicating the importance of methanotrophs. Phenoxy acid removal, using dichlorprop as a model compound, was further investigated in batch experiments with methanotrophic biomass collected from the enrichment reactors. Phenoxy acid removal (expressed per gram of matrix sand) was substantially improved in the methanotrophic enrichment compared to parent filter sand. The presence of methane did not clearly impact dichlorprop removal but did impact mineralization. We suggest that other heterotrophs are responsible for the first step in dichlorprop degradation, while the subsequent steps including ring-hydroxylation are driven by methanotrophs. Keywords: Drinking water; Methanotrophs; Pesticides; Phenoxy acids; Removal.

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.

Behavioural changes that occur during the parr–smolt transformation were investigated in juvenile coho salmon Oncorhynchus kisutch. Fish from two populations were examined from the Fraser River catchment in British Columbia, Canada; a short and a long‐distance migrating population. Fish showed a significant decrease in condition factor and significant increase in gill Na + K + ‐ATPase activity during the spring indicating that they became competent smolts, but no difference between populations. Temperature preference trials were conducted using a shuttlebox system throughout the spring. Mean temperature preference did not differ between the two populations, but preferred temperature decreased with development from 16.5 ± 0.3°C for parr to 15.5 ± 0.4°C for smolts. Mean swimming velocity was also greater in smolts than parr, but there was no difference between the two populations. The preference for warmer water temperature observed for parr in early spring may be advantageous for stimulating smolt development. Preference for slightly cooler temperatures observed for smolts would sustain elevated seawater tolerance during the smolt window by a short time and may ensure successful transition to the marine environment.

Phosphine is the only fumigant approved globally for general use to control insect pests in stored grain. Due to the emergence of resistance among insect pests and the lack of suitable alternative fumigants, we are investigating ways to synergistically enhance phosphine toxicity, by studying the mechanism of action of known synergists, such as oxygen, temperature, and arsenite. Under normoxia, exposure of the model organism Caenorhabditis elegans for 24 h at 20°C to 70 ppm phosphine resulted in 10% mortality, but nearly 100% mortality if the oxygen concentration was increased to 80%. In wild-type C. elegans, toxicity of phosphine was negatively affected by a decrease in temperature to 15°C and positively affected by an increase in temperature to 25°C. The dld-1(wr4) strain of C. elegans is resistant to phosphine due to a mutation in the dihydrolipoamide dehydrogenase gene. It also exhibits increased mortality that is dependent on hyperoxia, when exposed to 70 ppm phosphine at 20°C. As with the wild-type strain, mortality decreased when exposure was carried out at 15°C. At 25°C, however, the strain was completely resistant to the phosphine exposure at all oxygen concentrations. Arsenite is also a synergist of phosphine toxicity, but only in the dld-1(wr4)-mutant strain. Thus, exposure to 4 mM arsenite resulted in 50% mortality, which increased to 89% mortality when 70 ppm phosphine and 4 mM arsenite were combined. In stark contrast, 70 ppm phosphine rendered 4 mM arsenite nontoxic to wild-type C. elegans. These results reveal two synergists with distinct modes of action, one of which targets individuals that carry a phosphine resistance allele in the dihydrolipoamide dehydrogenase gene.

Annual hypoxia in the Chesapeake Bay has expanded to the point where Darwinian fitness of juvenile striped bass (Morone saxatilis) may depend on their ability to perform in low-oxygen environments. The locomotion they use in predator/prey dynamics relies primarily on white (type II) muscle that is powered by anaerobic metabolic pathways and has generally been thought to be immune to aquatic hypoxia. We tested the sprint performance of 15 juvenile striped bass twice under acute hypoxia (20% air saturation [AS]) 5 wk apart and once under normoxia (>85% AS) in between. Average sprint performance was lower under the first hypoxia exposure than in normoxia and increased in the second hypoxia test relative to the first. The rank order of individual sprint performance was significantly repeatable when comparing the two hypoxia tests but not when compared with sprint performance measured under normoxic conditions. The maximum sprint performance of each individual was also significantly repeatable within a given day. Thus, sprint performance of striped bass is reduced under hypoxia, is phenotypically plastic, and improves with repetitive hypoxia exposures but is unrelated to relative sprint performance under normoxia. Since energy to fuel a sprint comes from existing ATP and creatine phosphate stores, the decline in sprint performance probably reflects reduced function of a part of the reflex chain leading from detection of aversive stimuli to activation of the muscle used to power the escape response.

The Largemouth Bass Micropterus salmoides is the most sought-after species by recreational and tournament anglers in the United States. Survival of angled and tournament-handled Largemouth Bass has been related to numerous factors, but the independent effects of water temperature, angling time, and live-well dissolved oxygen (DO) concentration on survival have not been measured. Understanding the independent effects of these factors on fish survival is necessary to formulate realistic models to predict population effects of catch-and-release and tournament angling throughout the year. Survival responses to water temperature, angling time, and live-well DO concentration are also needed to develop guidelines useful for maximizing survival of released Largemouth Bass. Five-day survival of Largemouth Bass larger than 300 mm was evaluated after simulated catch-and-release and tournament handling (8 h of confinement in aerated live wells and a weigh-in before release) over the range of water temperatures typically encountered by Largemouth Bass anglers (17–33°C) while also testing independent effects of simulated angling time (1 and 3 min), live-well temperature change (∆T = 0, −4, and +4°C), and live-well DO (2.0, 5.5, and 8.5 mg/L). Survival of fish subjected to catch and immediate release was 100% at all temperatures measured, and survival of tournament-caught fish was over 80% at temperatures of 29°C or less but declined at 33°C. Survival decreased with increased simulated angling time at high temperatures and at a DO level of 2.0 mg/L in live wells. Survival rates and probabilities provided in this study should be considered best-case estimates because all fish were handled carefully and not subjected to hook wounding. However, results suggest that high survival of angled and tournament-handled Largemouth Bass is possible with short angling times and appropriate live-well management.

Many fish experience daily cycles of hypoxia in the wild, but the physiological strategies for coping with intermittent hypoxia are poorly understood. We examined how killifish adjust O2 supply and demand during acute hypoxia, and how these responses are altered after prolonged acclimation to constant or intermittent patterns of hypoxia exposure. We acclimated killifish to normoxia (∼20 kPa O2), constant hypoxia (2 kPa) or intermittent cycles of nocturnal hypoxia (12 h:12 h normoxia:hypoxia) for 28 days, and then compared whole-animal O2 consumption rates (ṀO2) and tissue metabolites during exposure to 12 h of hypoxia followed by reoxygenation in normoxia. Normoxia-acclimated fish experienced a pronounced 27% drop in ṀO2 during acute hypoxia, and modestly increased ṀO2 upon reoxygenation. They strongly recruited anaerobic metabolism during acute hypoxia, indicated by lactate accumulation in plasma, muscle, liver, brain, heart and digestive tract, as well as a transient drop in intracellular pH, and they increased hypoxia inducible factor (HIF)-1α protein abundance in muscle. Glycogen, glucose and glucose-6-phosphate levels suggested that glycogen supported brain metabolism in hypoxia, while the muscle used circulating glucose. Acclimation to constant hypoxia caused a stable ∼50% decrease in ṀO2 that persisted after reoxygenation, with minimal recruitment of anaerobic metabolism, suggestive of metabolic depression. By contrast, fish acclimated to intermittent hypoxia maintained sufficient O2 transport to support normoxic ṀO2, modestly recruited lactate metabolism and increased ṀO2 dramatically upon reoxygenation. Both groups of hypoxia-acclimated fish had similar glycogen, ATP, intracellular pH and HIF-1α levels as normoxic controls. We conclude that different patterns of hypoxia exposure favour distinct strategies for matching O2 supply and O2 demand.

Group‐living is widespread among animals and comes with numerous costs and benefits. To date, research examining group‐living has focused on trade‐offs surrounding foraging, while other forms of resource acquisition have been largely overlooked. Air‐breathing has evolved in many fish lineages, allowing animals to obtain oxygen in hypoxic aquatic environments. Breathing air increases the threat of predation, so some species perform group air‐breathing, to reduce individual risk. Within species, individual air‐breathing can be influenced by metabolic rate as well as personality, but the mechanisms of group air‐breathing remain unexplored. It is conceivable that keystone individuals with high metabolic demand or intrinsic tendency to breathe air may drive social breathing, especially in hypoxia. We examined social air‐breathing in African sharptooth catfish Clarias gariepinus, to determine whether individual physiological traits and spontaneous tendency to breathe air influence the behaviour of entire groups, and whether such influences vary in relation to aquatic oxygen availability. We studied 11 groups of four catfish in a laboratory arena and recorded air‐breathing behaviour, activity and agonistic interactions at varying levels of hypoxia. Bimodal respirometry was used to estimate individual standard metabolic rate ( SMR ) and the tendency to utilize aerial oxygen when alone. Fish took more air breaths in groups as compared to when they were alone, regardless of water oxygen content, and displayed temporally clustered air‐breathing behaviour, consistent with existing definitions of synchronous air‐breathing. However, groups displayed tremendous variability in surfacing behaviour. Aggression by dominant individuals within groups was the main factor influencing air‐breathing of the entire group. There was no association between individual SMR, or the tendency to obtain oxygen from air when in isolation, and group air‐breathing. For C. gariepinus, synchronous air‐breathing is strongly influenced by agonistic interactions, which may expose subordinate individuals to risk of predation. Influential individuals exerted an overriding effect on risk‐taking by the entire group, for reasons independent of their physiological oxygen requirements. Overall, this illustrates that social context can obscure interactions between an individual's physiological and behavioural traits and their tendency to take risks to obtain resources.

There is a growing amount of empirical evidence on the important role of cell size in body size adjustment in ambient or changing conditions. Though the adaptive significance of their correspondence is well understood and demonstrated, the proximate mechanisms are still in a phase of speculation. We made interesting observations on body/cell size adjustment under stressful conditions during an experiment designed for another purpose. We found that the strength of the body/cell size match is condition-dependent. Specifically, it is stronger under more stressful conditions, and it changes depending on exposure to lower temperature vs. exposure to higher temperature. The question whether these observations are of limiting or adaptive character remains open; yet, according to our results, both versions are possible but may differ in response to stress caused by too low vs. too high temperatures. Our results suggest that testing the hypotheses on body/cell size match may be a promising study system for the recent scientific dispute on the evolutionary meaning of developmental noise as opposed to phenotypic plasticity.

Prior work has described a link between an individual’s metabolic rate and a willingness to take risks. One context in which high metabolic rates and risk-prone behaviors may prove to be maladaptive is in fish that strike fishing lures only to be captured by anglers. It has been shown that metabolic phenotype may be altered by angling; however, little work has assessed metabolic rate in fish and its relationship to angling vulnerability in a realistic angling trial. To address this, we subjected a set of bluegill sunfish (Lepomis macrochirus Rafinesque, 1819) to a series of angling sessions. Following this, a subset of 23 fish that had been captured at least once and 25 fish that had not been captured were assessed for metabolic phenotype (standard and maximum metabolic rates, postexercise oxygen consumption, and recovery time) via intermittent flow respirometry. Contrary to predictions, captured and uncaptured fish did not differ in any measurement of metabolic rate. These results suggest that metabolic phenotype is not a determinant of angling vulnerability within the studied context. It is possible, therefore, that previously described alterations in metabolic phenotype owing to angling pressure may be context-specific and may not apply to all species and angling contexts.

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.

The increasing usage of nanoparticles has caused their considerable release into the aquatic environment. Meanwhile, anthropogenic CO 2 emissions have caused a reduction of seawater pH. However, their combined effects on marine species have not been experimentally evaluated. This study estimated the physiological toxicity of nano-TiO 2 in the mussel Mytilus coruscus under high pCO 2 (2500–2600 μatm). We found that respiration rate (RR), food absorption efficiency (AE), clearance rate (CR), scope for growth (SFG) and O:N ratio were significantly reduced by nano-TiO 2, whereas faecal organic weight rate and ammonia excretion rate (ER) were increased under nano-TiO 2 conditions. High pCO 2 exerted lower effects on CR, RR, ER and O:N ratio than nano-TiO 2. Despite this, significant interactions of CO 2 -induced pH change and nano-TiO 2 were found in RR, ER and O:N ratio. PCA showed close relationships among most test parameters, i.e., RR, CR, AE, SFG and O:N ratio. The normal physiological responses were strongly correlated to a positive SFG with normal pH and no/low nano-TiO 2 conditions. Our results indicate that physiological functions of M. coruscus are more severely impaired by the combination of nano-TiO 2 and high pCO 2.

Despite the use of fish models to study human mental disorders and dysfunctions, knowledge of regional telencephalic responses in non-mammalian vertebrates expressing alternate stress coping styles is poor. Since perception of salient stimuli associated with stress coping in mammals is mainly under forebrain limbic control, we tested region-specific forebrain neural (i.e. mRNA abundance and monoamine neurochemistry) and endocrine responses at basal and acute stress conditions for previously characterised proactive and reactive Atlantic salmon. Reactive fish show a higher degree of the neurogenesis marker proliferating cell nuclear antigen (pcna) and dopamine activity under basal conditions in Dl (proposed hippocampus homologue) and higher post-stress plasma cortisol levels. Proactive fish displayed post-stress higher serotonergic signalling (i.e. higher serotonergic activity and expression of the 5-HT1A receptor abundance) in the proposed amygdala homologue (Dm), increased expression of the neuroplasticity marker brain derived neurotropic factor (bdnf) in both Dl and Vv (lateral septum homologue), as well as increased expression of the corticotropin releasing factor 1 (crf1) receptor in the Dl, in line with active coping neuro-profiles reported in the mammalian literature. We present novel evidence of proposed functional equivalences in the fish forebrain with mammalian limbic structures.

The present study describes and validates a novel yet simple system for simultaneous in vivo measurements of aquatic CO2 production (MCO2) and oxygen consumption (MO2) rates, thus allowing the calculation of respiratory exchange ratios (RER). Diffusion of CO2 from the aquatic phase into a gas phase, across a hollow fibre membrane, enabled aquatic MCO2 measurements with a high-precision infrared gas CO2 analyser. MO2 was measured with a PO2 optode using a stop-flow approach. Injections of known amounts of CO2 into the apparatus yielded accurate and highly reproducible measurements of CO2 content (R2=0.997, p<0.001). The viability of in vivo measurements was demonstrated on aquatic dragonfly nymphs (Aeshnidae; wet mass 2.17 mg - 1.46 g, n=15) and the apparatus produced precise MCO2 (R2=0.967, p<0.001) and MO2 (R2=0.957, p<0.001); average RER was 0.73±0.06. The described system is scalable, offering great potential for the study of a wide range of aquatic species, including fish.

Hagfish are capable of tolerating extreme hypercapnia (> 30 Torr) by mounting substantial plasma [HCO3−] (hypercarbia) to compensate for CO2-mediated acidosis. The goal of this study was to characterize the mechanistic hypercarbia-recovery strategies in the highly CO2 tolerant hagfish. We exposed hagfish to hypercapnia (30 Torr) for 48 h and allowed a 24 h recovery period in normocapnic seawater. Within 8 h of the recovery period, the compensatory plasma [HCO3−] load (~ 70 mmol L−1) was rapidly offloaded. While increases in both whole-animal HCO3− excretion and glomerular filtration were observed throughout recovery (2–8 h), neither can fully account for the observed rates of whole-animal HCO3− loss, which peaked at ~ 3.5 mmol kg−1 h−1. Inhibition of carbonic anhydrase via acetazolamide revealed that the restoration of plasma [HCO3−] from hypercapnia-induced hypercarbia is likely facilitated in a dualistic manner, initially relying on both carbonic anhydrase mediated CO2 offloading and Cl−/HCO3− exchange processes, both of which are likely either upregulated or further activated as recovery progresses.

Rising ocean temperatures are predicted to cause a poleward shift in the distribution of marine fishes occupying the extent of latitudes tolerable within their thermal range boundaries. A prevailing theory suggests that the upper thermal limits of fishes are constrained by hypoxia and ocean acidification. However, some eurythermal fish species do not conform to this theory, and maintain their upper thermal limits in hypoxia. Here we determine if the same is true for stenothermal species. In three coral reef fish species we tested the effect of hypoxia on upper thermal limits, measured as critical thermal maximum (CT max ). In one of these species we also quantified the effect of hypoxia on oxygen supply capacity, measured as aerobic scope (AS). In this species we also tested the effect of elevated CO 2 (simulated ocean acidification) on the hypoxia sensitivity of CT max. We found that CT max was unaffected by progressive hypoxia down to approximately 35 mmHg, despite a substantial hypoxia-induced reduction in AS. Below approximately 35 mmHg, CT max declined sharply with water oxygen tension ( P w O 2 ). Furthermore, the hypoxia sensitivity of CT max was unaffected by elevated CO 2. Our findings show that moderate hypoxia and ocean acidification do not constrain the upper thermal limits of these tropical, stenothermal fishes.

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.

Ocean acidification is predicted to have detrimental effects on many marine organisms and ecological processes. Despite growing evidence for direct impacts on specific species, few studies have simultaneously considered the effects of ocean acidification on individuals (e.g. consequences for energy budgets and resource partitioning) and population level demographic processes. Here we show that ocean acidification increases energetic demands on gastropods resulting in altered energy allocation, i.e. reduced shell size but increased body mass. When scaled up to the population level, long-term exposure to ocean acidification altered population demography, with evidence of a reduction in the proportion of females in the population and genetic signatures of increased variance in reproductive success among individuals. Such increased variance enhances levels of short-term genetic drift which is predicted to inhibit adaptation. Our study indicates that even against a background of high gene flow, ocean acidification is driving individual- and population-level changes that will impact eco-evolutionary trajectories.

Most marine teleosts defend blood pH during high CO2 exposure by sustaining elevated levels of HCO3(-) in body fluids. In contrast to the gill, where measures are taken to achieve net base retention, elevated CO2 leads to base loss in the intestine of marine teleosts studied to date. This loss is thought to occur through transport pathways previously demonstrated to be involved with routine osmoregulation in marine teleosts. The main objective of this study was to characterize the intestinal transport physiology of the gulf toadfish (Opsanus beta) when exposed to varied levels of CO2: control, 5,000, 10,000, and 20,000 μatm CO2 (0.04, 0.5, 1, and 2 kPa, respectively). Results of this study suggest that intestinal apical anion exchange is highly responsive to hypercarbia, evidenced by a dose-dependent increase in intestinal luminal HCO3(-) (mmol L(-1)) that was mirrored by a reduction in Cl(-) (mmol L(-1)). Despite activation of HCO3(-) transport pathways typically used during osmoregulation, fractional fluid absorption was only significantly lower at the highest level of CO2. Although increased HCO3(-) excretion could provide more substrate for intestinally produced carbonates, carbonate production was not significantly increased during hypercarbia at the levels tested. This study is among the first to thoroughly characterize how compensation for elevated CO2 affects transport physiology and carbonate production in the marine fish intestine. This deeper understanding may be particularly relevant when considering the impacts of future predicted ocean acidification, where prolonged base loss may alter the energetic cost of acid-base balance or osmoregulation in marine fish.

Stress during fish culture alters physiological homeostasis and affects fillet quality. Maintenance of high‐quality seafood is important to ensure the production of a marketable product. This study assessed how sequential stressors affect the sensory and quality characteristics of catfish ( Ictalurus punctatus ) fillets. Three stress trials were conducted where temperature (25 or 33 °C) and dissolved oxygen (DO, approximately 2.5 or >5 mg/L) were manipulated followed by socking and transport stress. After each stage of harvest (environmental stress, socking, and transport), fillet yield, consumer acceptability, descriptive evaluation, cook loss, tenderness, and pH were evaluated. Fillet yield decreased with increasing severity of environmental stress. Fillets from the severe stress treatment (33 °C, approximately 2.5 mg/L) received the highest acceptability scores ( P < 0.05). Control fillets (25 °C, >5 mg/L) were the least acceptable ( P < 0.05). Increased intensity of less favorable flavor attributes commonly associated with catfish resulted in the differences in acceptability among treatments. As fish progressed through the harvest event, cook loss decreased, tenderness increased, and pH increased, indicating that stress induced textural changes. The data suggest that although environmental stress results in slight changes in flavor attributes, its effects on acceptability are minor with fillets from all treatments still liked (>6 on a 9 point scale). Socking and transport were identified to positively affect textural characteristics of catfish fillets. Although the effects observed were not likely to negatively impact consumer acceptance, a strict management plan should be followed to maintain consistency in the product and avoid changes in stressors that might alter quality more drastically.

Temperature-induced limitations on the capacity of the cardiorespiratory system to transport oxygen from the environment to the tissues, manifested as a reduced aerobic scope (maximum- minus standard metabolic rate), have been proposed as the principal determinant of the upper thermal limits of fishes and other water-breathing ectotherms. Consequently, the upper thermal niche boundaries of these animals are expected to be highly sensitive to aquatic hypoxia and other environmental stressors that constrain their cardiorespiratory performance. However, the generality of this dogma has recently been questioned, as some species have been shown to maintain aerobic scope at thermal extremes. Here, we experimentally tested whether reduced oxygen availability due to aquatic hypoxia would decrease the upper thermal limits (i.e., the critical thermal maximum; CT_max) of the estuarine red drum (Sciaenops ocellatus) and the marine lumpfish (Cyclopterus lumpus). In both species, CT_max was independent of oxygen availability over a wide range of oxygen levels despite substantial reductions in aerobic scope (i.e.,>72%). These data show that the upper thermal limits of water-breathing ectotherms are not always linked to the capacity for oxygen transport. Consequently, we propose a novel metric for classifying oxygen-dependence of thermal tolerance; the oxygen limit for thermal tolerance (P_(CT_max )), which is the water oxygen tension (P_w O_2) where an organism's CT_max starts to decline. We suggest that this metric can be used for assessing the oxygen sensitivity of upper thermal limits in water-breathing ectotherms, and the susceptibility of their upper thermal niche boundaries to environmental hypoxia.

Many fish encounter hypoxia in their native environment, but the role of mitochondrial physiology in hypoxia acclimation and hypoxia tolerance is poorly understood. We investigated the effects of hypoxia acclimation on mitochondrial respiration, O2 kinetics, emission of reactive oxygen species (ROS), and antioxidant capacity in the estuarine killifish (Fundulus heteroclitus). Killifish were acclimated to normoxia, constant hypoxia (5 kPa O2), or intermittent diel cycles of nocturnal hypoxia (12 h normoxia: 12 h hypoxia) for 28-33 days and mitochondria were isolated from liver. Neither pattern of hypoxia acclimation affected the respiratory capacities for oxidative phosphorylation or electron transport, leak respiration, coupling control, or phosphorylation efficiency. Hypoxia acclimation also had no effect on mitochondrial O2 kinetics, but P50 (the O2 tension at which hypoxia inhibits respiration by 50%) was lower in the leak state than during maximal respiration, and killifish mitochondria endured anoxia-reoxygenation without any impact on mitochondrial respiration. However, both patterns of hypoxia acclimation reduced the rate of ROS emission from mitochondria when compared at a common O2 tension. Hypoxia acclimation also increased the levels of protein carbonyls and the activities of superoxide dismutase and catalase in liver tissue (the latter only occurred in constant hypoxia). Our results suggest that hypoxia acclimation is associated with changes in mitochondrial physiology that decrease ROS production and may help improve hypoxia tolerance.

To date, numerous studies have shown negative impacts of CO2-acidified seawater (i.e. ocean acidification, OA) on marine organisms including calcifying invertebrates and fishes; however, limited research has been conducted on the physiological effects of OA on polar fishes and even less on the impacts of OA on early developmental stages of polar fishes. We evaluated aspects of aerobic metabolism and cardiorespiratory physiology of juvenile emerald rockcod Trematomus bernacchii, an abundant fish in the Ross Sea, Antarctica, to elevated partial pressure of carbon dioxide (pCO2) (420 [Ambient], 650 [Moderate] and 1050 [High] μtam pCO2) over a one-month period. We examined cardiorespiratory physiology including heart rate, stroke volume, cardiac output and ventilation, whole organism metabolism via oxygen consumption rate, and sub-organismal aerobic capacity by citrate synthase enzyme activity. Juvenile fish showed an increase in ventilation rate under High pCO2 compared to Ambient pCO2, while cardiac performance, oxygen consumption, and citrate synthase activity were not significantly affected by elevated pCO2. Acclimation time did have a significant effect on ventilation rate, stroke volume, cardiac output and citrate synthase activity, such that all metrics increased over the 4-week exposure period. These results suggest that juvenile emerald rockcod are robust to near-future increases in OA and may have the capacity to adjust for future increases in pCO2 by increasing acid-base compensation through increased ventilation.

The nests of embryonic turtles naturally experience elevated CO2 (hypercarbia), which leads to increased blood PCO2 and a respiratory acidosis resulting in reduced blood pH [extracellular pH (pHe)]. Some fishes preferentially regulate tissue pH [intracellular pH (pHi)] against changes in pHe; this has been proposed to be associated with exceptional CO2 tolerance and has never been identified in amniotes. As embryonic turtles may be CO2 tolerant based on nesting strategy, we hypothesized that they preferentially regulate pHi, conferring tolerance to severe acute acid-base challenges. This hypothesis was tested by investigating pH regulation in common snapping turtles (Chelydra serpentina) reared in normoxia then exposed to hypercarbia (13kPa PCO2) for 1h at three developmental ages, 70 and 90% of incubation, and in yearlings. Hypercarbia reduced pHe but not pHi, at all developmental ages. At 70% of incubation, pHe was depressed by 0.324 pH units while pHi of brain, white muscle, and lung increased; heart, liver, and kidney pHi remained unchanged. At 90% of incubation, pHe was depressed by 0.352 pH units but heart pHi increased with no change in pHi of other tissues. Yearling exhibited a pHe reduction of 0.235 pH units but had no changes in pHi of any tissues. The results indicate common snapping turtles preferentially regulate pHi during development, but the degree of the response is reduced throughout development. This is the first time preferential pHi regulation has been identified in an amniote. These findings may provide insight into the evolution of acid-base homeostasis during development of amniotes, and vertebrates in general.

Aerobic scope (AS) has been proposed as a functional measurement that can be used to make predictions about the thermal niche of aquatic ectotherms and hence potential fitness outcomes under future warming scenarios. Some salmonid species and populations, for example, have been reported to exhibit different thermal profiles for their AS curves such that AS peaks around the modal river temperature encountered during the upriver spawning migration, suggesting species- and population-level adaptations to river temperature regimes. Interestingly, some other salmonid species and populations have been reported to exhibit AS curves that maintain an upwards trajectory throughout the ecologically-relevant temperature range rather than peaking at a modal temperature. To shed further light on this apparent dichotomy, we used adult coho salmon (Onchorhynchus kisutch) to test the prediction that peak AS coincides with population-specific, historically experienced river temperatures. We assessed AS at 10°C and 15°C, which represent a typical river migration temperature and the upper limit of the historically experienced temperature range, respectively. We also examined published data on AS in juvenile coho salmon in relation to new temperature data measured from their freshwater rearing environments. In both cases, AS was either maintained or increased modestly throughout the range of ecologically relevant temperatures. In light of existing evidence and the new data presented here, we suggest that when attempting to understand thermal optima for Pacific salmon and other species across life stages, AS is a useful metric of oxygen transport capacity but other thermally-sensitive physiological indices of performance and fitness should be considered in concert.

Air breathing in fish is commonly believed to have arisen as an adaptation to aquatic hypoxia. The effectiveness of air breathing for tissue O2 supply depends on the ability to avoid O2 loss as oxygenated blood from the air-breathing organ passes through the gills. Here, we evaluated whether the armoured catfish (Hypostomus aff. pyreneusi)—a facultative air breather—can avoid branchial O2 loss while air breathing in aquatic hypoxia, and we measured various other respiratory and metabolic traits important for O2 supply and utilization. Fish were instrumented with opercular catheters to measure the O2 tension (PO2) of expired water, and air breathing and aquatic respiration were measured during progressive stepwise hypoxia in the water. Armoured catfish exhibited relatively low rates of O2 consumption and gill ventilation, and gill ventilation increased in hypoxia due primarily to increases in ventilatory stroke volume. Armoured catfish began air breathing at a water PO2 of 2.5 kPa, and both air-breathing frequency and hypoxia tolerance (as reflected by PO2 at loss of equilibrium, LOE) was greater in individuals with a larger body mass. Branchial O2 loss, as reflected by higher PO2 in expired than in inspired water, was observed in a minority (4/11) of individuals as water PO2 approached that at LOE. Armoured catfish also exhibited a gill morphology characterized by short filaments bearing short fused lamellae, large interlamellar cell masses, low surface area, and a thick epithelium that increased water-to-blood diffusion distance. Armoured catfish had a relatively low blood-O2 binding affinity when sampled in normoxia (P50 of 3.1 kPa at pH 7.4), but were able to rapidly increase binding affinity during progressive hypoxia exposure (to a P50 of 1.8 kPa). Armoured catfish also had low activities of several metabolic enzymes in white muscle, liver, and brain. Therefore, low rates of metabolism and gill ventilation, and a reduction in branchial gas-exchange capacity, may help minimize branchial O2 loss in armoured catfish while air breathing in aquatic hypoxia.

The critical thermal maximum (CTmax) and the associated hematological response of juvenile (~145 g, n = 8 for both species) Atlantic Acipenser oxyrinchus and shortnose Acipenser brevirostrum sturgeons acclimated to 15°C were determined using a heating rate of 8°C h−1. The critical thermal maximum averaged 30.8°C and 31.6°C for Atlantic and shortnose sturgeon, respectively, and values fell within the range noted for other sturgeon species. Oxygen-carrying capacity (hemoglobin and hematocrit) measures were generally unaffected by thermal stress. Plasma lactate levels increased from 0.5 mm to 4 mm following temperature stress in both species. Both plasma glucose and potassium levels increased following CTmax, however, these levels were about double in the shortnose sturgeon. Lastly, plasma sodium and chloride levels were significantly depressed (by more than 10%) following thermal stress in shortnose sturgeon, whereas only chloride levels decreased in Atlantic sturgeon. Taken together, while CTmax values were similar, thermal stress resulted in different hematological profiles; these differences are consistent when compared to other stressors, and may be related to the phylogenetic position and thus could reflect the evolutionary history of these two species.

In the past several years, all numerical models have forecasted an increase in extreme climatic events linked to global change. Estuarine waters at the interface of marine and freshwater bodies are among the most volatile ecosystems, particularly for aquatic species, and will be strongly influenced by the temperature with extreme flooding events. This study aimed to quantify the acclimation capacity of coastal fish species to estuarine plume modifications. The thicklip mullet (Chelon labrosus) and European seabass (Dicentrarchus labrax) were selected as representative species of estuarine ecological guilds. These fish were subjected to an experiment mimicking a brief freshwater intrusion (35–5). These experiments were conducted at two different temperatures that these two species would encounter during their incursion from the sea through estuarine waters to freshwater habitats. The experimental results confirmed the high capacity for acclimation of both species to changes in salinity and temperature. Interspecific differences were observed. For example, the salinity has a greater effect on the metabolism of the seabass than on that of the mullets. Meanwhile, the temperature has a greater effect on the mullets. These differences in metabolic responses to fluctuating salinities and temperatures may modify the use of estuarine waters by these species and should be considered when predicting future specific distribution areas in the context of global change

As global climate change progresses, the Southern Ocean surrounding Antarctica is poised to undergo potentially rapid and substantial changes in temperature and pCO2. To survive in this challenging environment, the highly cold adapted endemic fauna of these waters must demonstrate sufficient plasticity to accommodate these changing conditions or face inexorable decline. Previous studies of notothenioids have focused upon the short-term response to heat stress; and more recently the longer-term physiological response to the combined stress of increasing temperatures and pCO2. This inquiry explores the transcriptomic response of Trematomus bernacchii to increased temperatures and pCO2 at 7, 28 and 56 days, in an attempt to discern the innate plasticity of T. bernacchii available to cope with a changing Southern Ocean. Differential gene expression analysis supported previous research in that T. bernacchii exhibits no inducible heat shock response to stress conditions. However, T. bernacchii did demonstrate a strong stress response to the multi-stressor condition in the form of metabolic shifts, DNA damage repair, immune system processes, and activation of apoptotic pathways combined with negative regulation of cell proliferation. This response declined in magnitude over time, but aspects of this response remained detectable throughout the acclimation period. When exposed to the multi-stressor condition, T. bernacchii demonstrates a cellular stress response that persists for a minimum of 7 days before returning to near basal levels of expression at longer acclimation times. However, subtle changes in expression persist in fish acclimated for 56 days that may significantly affect the fitness T. bernacchii over time.

Lay In nature, vast differences in growth or size are frequently observed among young born to mothers of different age. However, it is unknown if there can be other, more subtle differences among offspring born to young versus old mothers? In Atlantic salmon, we reveal that despite being similar in size, juveniles from younger-maturing mothers are more aggressive, but poorer at competing for food than juveniles from older-maturing mothers

Locomotor performance is closely related to fitness. However, in many ecological contexts, animals do not move at their maximal locomotor capacity, but adopt a voluntary speed that is lower than maximal. It is important to understand the mechanisms that underlie voluntary speed, because these determine movement patterns of animals across natural environments. We show that voluntary speed is a stable trait in zebrafish (Danio rerio), but there were pronounced differences between individuals in maximal sustained speed, voluntary speed and metabolic cost of locomotion. We accept the hypothesis that voluntary speed scales positively with maximal sustained swimming performance (Ucrit), but only in unfamiliar environments (1st minute in an open-field arena versus 10th minute) at high temperature (30°C). There was no significant effect of metabolic scope on Ucrit. Contrary to expectation, we rejected the hypothesis that voluntary speed decreases with increasing metabolic cost of movement, except in familiar spatial (after 10 min of exploration) and thermal (24°C but not 18 or 30°C) environments. The implications of these data are that the energetic costs of exploration and dispersal in novel environments are higher than those for movement within familiar home ranges.

In freshwater ecosystems, abiotic factors such as flow regime and water quality are considered important predictors of ecosystem invasibility. The aim of this study was to investigate the critical swimming capacity and metabolism of the eastern mosquitofish, Gambusia holbrooki, focusing on sex and size effects, to evaluate the influence of water flow on its invasive success. Specimens of mosquitofish were captured from the Ter Vell lagoon (L'Estartit, north‐eastern Spain) in July 2014, and we measured the critical swimming speed ( U crit ) and oxygen consumption of individual fish (30 females and 30 males) using a mini swim tunnel. The mean U crit of this poeciliid fish was estimated at 14.11 cm·s −1 (range = 4.85–22.26), which is lower than that of many other fishes of similar size and confirms that this species is limnophilic and its invasive success might be partially explained by hydrologic alterations. However, the U crit and maximal metabolic rate vary markedly with fish size and sex, with males having much higher values for the same body mass, and thus probably being more resistant to strong water flows. Multiple regression models illustrate that multivariate analyses might increase the predictive power and understanding of swimming performance and metabolic traits, compared to results from conventional simple regressions.

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.

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.

Cold-water corals, such as Lophelia pertusa, are key habitat-forming organisms found throughout the world's oceans to 3000 m deep. The complex three-dimensional framework made by these vulnerable marine ecosystems support high biodiversity and commercially important species. Given their importance, a key question is how both the living and the dead framework will fare under projected climate change. Here, we demonstrate that over 12 months L. pertusa can physiologically acclimate to increased CO 2, showing sustained net calcification. However, their new skeletal structure changes and exhibits decreased crystallographic and molecular-scale bonding organization. Although physiological acclimatization was evident, we also demonstrate that there is a negative correlation between increasing CO 2 levels and breaking strength of exposed framework (approx. 20–30% weaker after 12 months), meaning the exposed bases of reefs will be less effective ‘load-bearers’, and will become more susceptible to bioerosion and mechanical damage by 2100.

An improved understanding of bycatch mortality can be achieved by complementing field studies with laboratory experiments that use physiological assessments. This study examined the effects of water temperature and the duration of net entanglement on physiological disturbance and recovery in coho salmon (Oncorhynchus kisutch) after release from a simulated beach seine capture. Heart rate was monitored using implanted electrocardiogram biologgers that allowed fish to swim freely before and after release. A subset of fish was recovered in respirometers to monitor metabolic recovery, and separate groups of fish were sacrificed at different times to assess blood and white muscle biochemistry. One hour after release, fish had elevated lactate in muscle and blood plasma, depleted tissue energy stores, and altered osmoregulatory status, particularly in warmer (15 vs. 10°C) and longer (15 vs. 2 min) capture treatments. A significant effect of entanglement duration on blood and muscle metabolites remained after 4 h. Oxygen consumption rate recovered to baseline within 7–10 h. However, recovery of heart rate to routine levels was longer and more variable, with most fish taking over 10 h, and 33% of fish failing to recover within 24 h. There were no significant treatment effects on either oxygen consumption or heart rate recovery. Our results indicate that fishers should minimize handling time for bycatch and maximize oxygen supply during crowding, especially when temperatures are elevated. Physiological data, such as those presented here, can be used to understand mechanisms that underlie bycatch impairment and mortality, and thus inform best practices that ensure the welfare and conservation of affected species.

Understanding the impact of ocean acidification and warming on communities and ecosystems is a researcher priority. This can only be achieved through a combination of experimental and field approaches that would allow developing a mechanistic understanding of impacts across level of biological organizations. Surprisingly, most published studies are still focusing on single species responses with little consideration for interspecific interactions. In this study, the impacts of a 3 days exposure to three parameters (temperature, pH, and presence/absence of the predator cue of the crab Charybdis japonica) and their interactions on an ecologically important endpoint were evaluated: the byssus production of the mussel Mytilus coruscus. Tested temperatures (25°C and 30°C) were within the present range of natural variability whereas pH (8.1, 7.7, and 7.4) covered present as well as near-future natural variability. As expected, the presence of the crab cue induced an antipredator response in Mytilus coruscus (significant 10% increase in byssus secretion rate, 22% increase in frequency of shed byssus, and 30% longer byssus). Decreased pH but not temperature had a significant negative impact on the same endpoints (up to a 17% decrease in byssus secretion rate, 40% decrease in frequency of shed byssus, and 10% shorter byssus at pH 7.3 as compared with pH 8.1) with no significant interactions between the three tested parameters. In this study, it has been hypothesized that pH and predator cue have different modes of action and lead to conflicting functional responses (escape response versus stronger attachment). Functional consequences for ecosystem dynamics still need to be investigated.

Individual striped bass Morone saxatilis were each exposed in random order to aquatic hypoxia (10% air saturation) either while swimming at 50% of their estimated critical swimming speed ( U crit ) or while at rest until they lost equilibrium. Individuals were always less tolerant of hypoxia when swimming ( P

Nitrite secures essential nitric oxide (NO) bioavailability in hypoxia at low endogenous concentrations, whereas it becomes toxic at high concentrations. We exposed brown trout to normoxic and hypoxic water in the absence and presence of added ambient nitrite to decipher the cellular metabolism and effects of nitrite at basal and elevated concentrations under different oxygen regimes. We also tested hypotheses concerning influences of nitrite on branchial nitric oxide synthase (NOS), Na+/K+-ATPase (nka) and heat shock protein (hsp70) mRNA expression. Basal plasma and erythrocyte nitrite levels were higher in hypoxia than normoxia, suggesting increased NOS activity. Nitrite exposure strongly elevated nitrite concentrations in plasma, erythrocytes, heart tissue and white muscle, which was associated with an extensive metabolism of nitrite to nitrate and to iron-nitrosylated and S-nitrosated compounds. Nitrite uptake was slightly higher in hypoxia than normoxia, and high internal nitrite levels extensively converted blood hemoglobin to methemoglobin and nitrosylhemoglobin. Hypoxia increased inducible NOS (iNOS) mRNA levels in gills, which was overruled by a strong inhibition of iNOS expression by nitrite in both normoxia and hypoxia, suggesting negative feedback regulation of iNOS gene expression by nitrite. A similar inhibition was absent for neuronal NOS. Branchial NKA activity stayed unchanged, but mRNA levels of the NKA α1a subunit increased with hypoxia and nitrite, which may have countered an initial NKA inhibition. Nitrite also increased hsp70 gene expression, probably contributing to cytoprotective effects of nitrite at low concentrations. Nitrite displays a concentration-dependent switch between positive and negative effects resembling other signaling molecules.

Migratory fishes encounter a variety of environmental conditions, including changes in salinity, temperature and dissolved gases, and it is important to understand how these fishes are able to acclimate to multiple environmental stressors. The gill is the primary site of both acid–base balance and ion regulation in fishes. Many ion transport mechanisms involved with acid–base compensation are also required for the regulation of plasma Na+ and Cl+, the predominant extracellular ions, potentially resulting in a strong interaction between ionoregulation and acid–base regulation. The present study examined the physiological interaction of elevated dissolved CO2 (an acid–base disturbance) on osmoregulation during seawater acclimation (an ionoregulatory disturbance) in juvenile white sturgeon (Acipenser transmontanus). Blood pH (pHe), plasma [HCO3−], [Na+], [Cl−] and osmolality, white muscle water content, and gill Na+/K+-ATPase (NKA) and Na+/K+/2Cl− co-transporter (NKCC) abundance were examined over a 10 day seawater (SW) acclimation period under normocarbia (NCSW) or during prior and continued exposure to hypercarbia (HCSW), and compared with a normocarbic freshwater (NCFW) control. Hypercarbia induced a severe extracellular acidosis (from pH 7.65 to pH 7.2) in HCSW sturgeon, and these fish had a 2-fold greater rise in plasma osmolarity over NCSW by day 2 of SW exposure. Interestingly, pHe recovery in HCSW was associated more prominently with an elevation in plasma Na+ prior to osmotic recovery and more prominently with a reduction in plasma Cl− following osmotic recovery, indicating a biphasic response as the requirements of osmoregulation transitioned from ion-uptake to ion-excretion throughout SW acclimation. These results imply a prioritization of osmoregulatory recovery over acid–base recovery in this period of combined exposure to acid–base and ionoregulatory disturbances.

Hypoxia – which refers to insufficient amounts of oxygen in tissues – is an important pathophysiological driver of angiogenesis through a complicated web of signaling pathways, which are still incompletely understood. Zebrafish are as other fish species highly hypoxia-tolerant compared to mammals. Furthermore their skin and gills are highly permeable to orally active drugs added to the water, including the large number of small synthetic activators or inhibitors of various signaling pathways available today. This enables the specific study of hypoxia-induced signaling pathways leading to angiogenesis in living adult animals, a feature that is of high relevance in medical research and unique for this model system. In this chapter we provide detailed protocols for how to set up hypoxia systems, expose adult zebrafish to hypoxia or hyperoxia (elevated tissue oxygen levels), extract images of hypoxia-induced angiogenesis from the adult retina and methods for quantifying changes in angiogenesis from such images.

Vertebrate pigmentation is emerging as a powerful system for studying the evolution of adaptive traits and the maintenance of genetic and phenotypic variation in natural populations. Though melanism has been linked to physiological and behavioral traits in a variety of taxa, the generality of these associations for many taxa such as fishes remains unclear. Here I tested whether variation in melanism in a livebearing fish was correlated with a variety of traits often tested in other taxa: locomotor stress coping style during confinement, boldness in a novel environment, and metabolic rate. There were significant negative associations between an individual’s amount of melanistic pigmentation and both activity in confinement and boldness in a novel environment. In contrast with evidence from many prior studies, there was no relationship between melanism and metabolic rate. Overall, the data provide some support for documented relationships between melanism and behavioral traits, but did not support the generally reported relationship between melanism and metabolic rate. Links between melanism and behavioral coping strategies related to environmental stressors may have important implications for the evolution and maintenance of behavioral and morphological variation in natural populations. Nonetheless, these results also suggest variation among taxa in the extent to which pleiotropy has evolved between melanism and diverse organismal traits.

In the adult, new vessels and red blood cells form in response to hypoxia. Here, the oxygen-sensing system (PHD–HIF) has recently been put into focus, since the prolyl-hydroxylase domain proteins (PHD) and hypoxia-inducible factors (HIF) are considered as potential therapeutic targets to treat ischemia, cancers or age-related macula degeneration. While the oxygen-sensing system (PHD–HIF) has been studied intensively in this respect, only little is known from developing vertebrate embryos since mutations within this pathway led to an early decease of embryos due to placental defects. During vertebrate embryogenesis, a progenitor cell called hemangioblast is assumed to give rise to blood cells and blood vessels in a process called hematopoiesis and vasculogenesis, respectively. Xenopus provides an ideal experimental system to address these processes in vivo, as its development does not depend on a functional placenta and thus allows analyzing the role of oxygen directly. To this end, we adopted a computer-controlled four-channel system, which allowed us to culture Xenopus embryos under defined oxygen concentrations. Our data show that the development of vascular structures and blood cells is strongly impaired under hypoxia, while general development is less compromised. Interestingly, suppression of Phd2 function using specific antisense morpholinos or a chemical inhibitor resulted in mostly overlapping vascular defects; nevertheless, blood cell was formed almost normally. Our results provide the first evidence that oxygen via Phd2 has a decisive influence on the formation of the vascular network during vertebrate embryogenesis. These findings may be considered in certain potential treatment concepts.

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.

Bigheaded carps are non-native invasive fishes that have quickly become the most abundant fishes in many portions of the Midwestern United States. While the spread of bigheaded carps into the Great Lakes is currently impeded by three electrified barriers, these fish have the potential to negatively impact the Great Lakes ecosystem if this barrier is breached, and these barriers may be particularly vulnerable to the passage of small fishes. As such, novel barrier technologies would provide an additional mechanism to prevent bigheaded carps from invading the Great Lakes, and provide much needed redundancy to the current electric barrier. The current study used a combination of molecular and behavioral experiments to determine the effectiveness of carbon dioxide as a chemical deterrent for larval and juvenile fishes, with an emphasis on bigheaded carps. Juvenile silver carp (Hypophthalmichthys molitrix), bighead carp (H. nobilis), bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides) showed avoidance of elevated CO2 environments at approximately 200 mg/L. Additionally, exposure to 120 mg/L CO2 resulted in the induction of hsp70 mRNA in 8 days old silver carp fry, while gill c-fos transcripts increased following hypercarbia exposure in all juvenile species examined. Together, our results show that CO2 has potential to deter the movement of larval and juvenile fishes.

Biologging technology has enhanced our understanding of the ecology of marine animals and has been central to identifying how oceanographic conditions drive patterns in their distribution and behavior. Among these environmental influences, there is increasing recognition of the impact of dissolved oxygen on the distribution of marine animals. Understanding of the impact of oxygen on vertical and horizontal movements would be advanced by contemporaneous in situ measurements of dissolved oxygen from animal-borne sensors instead of relying on environmental data that may not have appropriate spatial or temporal resolution. Here, we demonstrate the capabilities of dissolved oxygen pop-up satellite archival tags (DO-PATs) by presenting the results from calibration experiments and trial deployments of two prototype tags on bluntnose sixgill sharks (Hexanchus griseus). The DO-PATs provided fast, accurate, and stable measurements in calibration trials and demonstrated high correlation with vertical profiles obtained via traditional ship-borne oceanographic instruments. Deployments on bluntnose sixgill sharks recorded oxygen saturations as low as 9.4 % and effectively captured the oceanography of the region when compared with World Ocean Atlas 2013 values. This is the first study to use an animal-borne device to autonomously measure and record in situ dissolved oxygen saturation from non-air-breathing marine animals. The DO-PATs maintained consistency over time and yielded measurements equivalent to industry standards for environmental sampling. Acquiring contemporaneous in situ measurements of dissolved oxygen saturation alongside temperature and depth data will greatly improve our ability to investigate the spatial ecology of marine animals and make informed predictions of the impacts of global climate change. The information returned from DO-PATs is relevant not only to the study of the ecology of marine animals but will also become a useful new tool for investigating the physical structure of the oceans.

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.

The transition to air-breathing by formerly aquatic species has occurred repeatedly and independently in fish, crabs and other animal phyla, but the proximate drivers of this key innovation remain a long-standing puzzle in evolutionary biology. Most studies attribute the onset of air-breathing to the repeated occurrence of aquatic hypoxia; however, this hypothesis leaves the current geographical distribution of the 300 genera of air-breathing crabs unexplained. Here, we show that their occurrence is mainly related to high environmental temperatures in the tropics. We also demonstrate in an amphibious crab that the reduced cost of oxygen supply in air extends aerobic performance to higher temperatures and thus widens the animal's thermal niche. These findings suggest that high water temperature as a driver consistently explains the numerous times air-breathing has evolved. The data also indicate a central role for oxygen- and capacity-limited thermal tolerance not only in shaping sensitivity to current climate change but also in underpinning the climate-dependent evolution of animals, in this case the evolution of air-breathing.

While bar-headed geese are renowned for migration at high altitude over the Himalayas, previous work on captive birds suggested that these geese are unable to maintain rates of oxygen consumption while running in severely hypoxic conditions. To investigate this paradox, we re-examined the running performance and heart rates of bar-headed geese and barnacle geese (a low altitude species) during exercise in hypoxia. Bar-headed geese (n = 7) were able to run at maximum speeds (determined in normoxia) for 15 minutes in severe hypoxia (7% O2; simulating the hypoxia at 8500 m) with mean heart rates of 466±8 beats min−1. Barnacle geese (n = 10), on the other hand, were unable to complete similar trials in severe hypoxia and their mean heart rate (316 beats.min−1) was significantly lower than bar-headed geese. In bar-headed geese, partial pressures of oxygen and carbon dioxide in both arterial and mixed venous blood were significantly lower during hypoxia than normoxia, both at rest and while running. However, measurements of blood lactate in bar-headed geese suggested that anaerobic metabolism was not a major energy source during running in hypoxia. We combined these data with values taken from the literature to estimate (i) oxygen supply, using the Fick equation and (ii) oxygen demand using aerodynamic theory for bar-headed geese flying aerobically, and under their own power, at altitude. This analysis predicts that the maximum altitude at which geese can transport enough oxygen to fly without environmental assistance ranges from 6,800 m to 8,900 m altitude, depending on the parameters used in the model but that such flights should be rare.

A before‐after‐control‐impact ( BACI ) experiment was conducted to examine the effects of hydraulic clam dredging on sediment biogeochemistry of a leased shellfish bed of Mercenaria mercenaria, northern quahog, over the course of an entire growing season. Six study plots (0.67 ha each), three dredged and three not dredged, off of Milford, Connecticut, in Long Island Sound, were sampled from May to October 2009 for porewater fluxes of total ammonia, oxygen, and hydrogen. Particulate samples were also analyzed for grain size, total nitrogen, total carbon, total sulfur, and organic carbon. Statistical analysis indicated no significant difference between dredged and not dredged sites. Grain size and oxygen flux explained 22% of the variation in the total benthic species assemblages; grain size and either total carbon or organic nitrogen explained 18% of the variation in molluscan abundance. Our study demonstrates that one‐time hydraulic shellfish harvesting had minor effects on the sediment chemistry of a leased clam bed.

Antarctic fish of the suborder Notothenioidei have evolved several unique adaptations to deal with subzero temperatures. However, these adaptations may come with physiological trade-offs, such as an increased susceptibility to oxidative damage. As such, the expected environmental perturbations brought on by global climate change have the potential to significantly increase the level of oxidative stress and cellular damage in these endemic fish. Previous single stressor studies of the notothenioids have shown they possess the capacity to acclimate to increased temperatures, but the cellular level effects remain largely unknown. Additionally, there is little information on the ability of Antarctic fish to respond to ecologically relevant environmental changes where multiple variables change co-comittently. We have examined the potential synergistic effects increased temperature and pCO2 have on the level of protein damage in Trematomus bernacchii, Pagothenia borchgrevinki, and Trematomus newnesi, and combined these measurements with changes in total enzymatic activity of catalase (CAT) and superoxide dismutase (SOD) in order to gauge tissue-specific changes in antioxidant capacity. Our findings indicate that total SOD and CAT activity levels displayed only small changes across treatments and tissues. Short-term acclimation to decreased seawater pH and increased temperature resulted in significant increases in oxidative damage. Surprisingly, despite no significant change in antioxidant capacity, cellular damage returned to near basal levels, and in T. bernacchii, significantly decreased, after long-term acclimation. Overall, these data suggest notothenioid fish currently maintain the antioxidant capacity necessary to offset predicted future ocean conditions, but it remains unclear if this capacity comes with physiological trade-offs.

To address how capacity for oxygen transport influences tolerance of acute warming in fishes, we investigated whether a reduction in haematocrit, by means of intra-peritoneal injection of the haemolytic agent phenylhydrazine, lowered upper critical temperature of sea bass. A reduction in haematocrit from 42±2 to 20±3% (mean ± s.e.m.) caused a significant but minor reduction in upper critical temperature, from 35.8 ± 0.1 to 35.1±0.2°C, with no correlation between individual values for haematocrit and upper thermal limit. Anaemia did not influence the rise in oxygen uptake between 25 and 33°C, because the anaemic fish were able to compensate for reduced blood oxygen carrying capacity with a significant increase in cardiac output. Therefore, in sea bass the upper critical temperature, at which they lost equilibrium, was not determined by an inability of the cardio-respiratory system to meet the thermal acceleration of metabolic demands.

During the years 2010–13, atmospheric eddy covariance measurement of oxygen was performed at the marine site Östergarnsholm in the Baltic Sea. The fast response optode Microx TX3 was used with two different types of tapered sensors. In spite of the increased lifetime, the optical isolated sensor is limited by the slower response time and is unsuitable for ground-based eddy covariance measurements. The sensor without optical isolation shows a −⅔ slope within the inertial subrange and attains sufficient response time and precision to be used in air–sea applications during continuous periods of 1–4 days. Spectral and cospectral analysis shows oxygen measured with the nonoptical isolated sensor to follow the same shape as for CO 2 and water vapor when normalized. The sampling rate of the Microx TX3 is 2 Hz; however, the sensor was found to have a limited response and resolution, yielding a flux loss in the frequency range f > 0.3 Hz. This can be corrected for by applying cospectral similarity simultaneously using measurements of latent heat as the reference signal. On average the magnitude of the cospectral correction added 20% to the uncorrected oxygen flux during neutral atmospheric stratification.

Reduced metabolic rates of groundwater taxa, compared to those of surface water species, have long been inferred to be an adaptive trait where there is a low and discontinuous food supply and unpredictable shifts between hypoxic and normoxic conditions. However, there have been neither measurements of the respiratory rate of groundwater copepods nor a comparison of rates between closely related groundwater and surface water species. We measured the metabolic rates of two species of Cyclopoida: Cyclopidae, the stygobiotic (hypogean) copepod Diacyclops belgicus and the epigean Eucyclops serrulatus, which co‐occur in the same alluvial aquifer. We expected the metabolic rate of the hypogean to be lower than that of the epigean species, irrespective of the ontogenetic stage, which would be consistent with the hypothesis that there is a generally lower metabolic rate in groundwater species. The metabolic rate of D. belgicus was significantly lower than that of the epigean E. serrulatus irrespective of the ontogenetic stage. We found an allometric relationship between oxygen consumption and body mass for E. serrulatus, an isometric one for D. belgicus juveniles and a rate of oxygen consumption that apparently does not change systematically with body mass for D. belgicus adults. The low metabolic rate of D. belgicus may be advantageous in oligotrophic groundwater habitats, where large fluctuations in oxygen availability occur. However, these physiological adaptations can put hypogean species at risk of replacement by more metabolically active epigean taxa, whenever the availability of organic matter increases, as happens with organic pollution. Moreover, the low metabolic rate of the hypogean species may entail an inability to cope with toxicants, rendering them more sensitive to pollutants. A higher metabolic rate in juvenile D. belgicus compared to that of adults allows copepodids to mature quickly when food is briefly abundant.

Cold-water corals are associated with high local biodiversity, but despite their importance as ecosystem engineers, little is known about how these organisms will respond to projected ocean acidification. Since preindustrial times, average ocean pH has decreased from 8.2 to ~8.1, and predicted CO2 emissions will decrease by up to another 0.3 pH units by the end of the century. This decrease in pH may have a wide range of impacts upon marine life, and in particular upon calcifiers such as cold-water corals. Lophelia pertusa is the most widespread cold-water coral (CWC) species, frequently found in the North Atlantic. Here, we present the first short-term (21 days) data on the effects of increased CO2 (750 ppm) upon the metabolism of freshly collected L. pertusa from Mingulay Reef Complex, Scotland, for comparison with net calcification. Over 21 days, corals exposed to increased CO2 conditions had significantly lower respiration rates (11.4±1.39 SE, µmol O2 g?1 tissue dry weight h?1) than corals in control conditions (28.6±7.30 SE µmol O2 g?1 tissue dry weight h?1). There was no corresponding change in calcification rates between treatments, measured using the alkalinity anomaly technique and 14C uptake. The decrease in respiration rate and maintenance of calcification rate indicates an energetic imbalance, likely facilitated by utilisation of lipid reserves. These data from freshly collected L. pertusa from the Mingulay Reef Complex will help define the impact of ocean acidification upon the growth, physiology and structural integrity of this key reef framework forming species.

Ocean acidification, resulted from high level of carbon dioxide (CO2) dissolved in seawater, may disturb the physiology of fish in many ways. However, it is unclear how acidification may impact the growth rate and/or growth hormones of marine fish. In this study, we exposed juvenile orange-spotted groupers (Epinephelus coioides )t o seawater of different levels of acidification: a condition predicted by the Intergovernmental Panel on Climate Change (pH 7.8–8.0), and a more extreme condition (pH 7.4–7.6) that may occur in coastal waters in the near future. After 6 weeks of exposure, the growth rates of fish in pH 7.4–7.6 were less than those raised in control water (pH 8.1–8.3). Furthermore, exposure at pH 7.4–7.6 increased blood pCO2 and HCO3 � significantly; exposure at pH 7.8–8.0, meanwhile, did not affect acid–base chemistry. Moreover, exposure to pH 7.4–7.6 resulted in lower levels of hepatic igf1 (insulin-like growth factor I) mRNA, but did not affect levels of pituitary gh (growth hormone) or hypothalamus psst2 and psst3 (prepro-somatostatin II and III). The results show that highly acidified seawater suppresses growth of juvenile grouper, which may be a consequence of reduced levels of IGF-1, but not due to diminished growth hormone release.

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.

In watersheds of equatorial West Africa, monophyletic groups of killifish species (genus Aphyosemion) occur in discrete altitudinal ranges, low altitude species (LA, sea level to ∼350 m) or high altitude species (HA, 350 to 900 m). We investigated the hypothesis that local adaptation to altitude by the LA and HA species would be revealed as divergent effects of temperature on their physiological energetics. Two species from each group (mass ∼350 mg) were acclimated to 19, 25 and 28°C, with 19 and 28°C estimated to be outside the thermal envelope for LA or HA, respectively, in the wild. Wild-caught animals (F0 generation) were compared with animals raised in captivity at 25°C (F1 generation) to investigate the contribution of adaptation versus plasticity. Temperature significantly increased routine metabolic rate in all groups and generations. However, LA and HA species differed in the effects of temperature on their ability to process a meal. At 25°C, the specific dynamic action (SDA) response was completed within 8 h in all groups, but acclimation to temperatures beyond the thermal envelope caused profound declines in SDA performance. At 19°C, the LA required ∼14 h to complete the SDA, whereas the HA required only ∼7 h. The opposite effect was observed at 28°C. This effect was evident in both F0 and F1. Reaction norms for effects of temperature on SDA therefore revealed a trade-off, with superior performance at warmer temperatures by LA being associated with inferior performance at cooler temperatures, and vice-versa in HA. The data indicate that divergent physiological responses to temperature in the LA and HA species reflect local adaptation to the thermal regime in their habitat, and that local adaptation to one thermal environment trades off against performance in another.

We develop a swimming costs model that accounts for the influence of flow velocity and body weight on the net active metabolic rate of Murray cod (Maccullochella peelii). Laboratory trials indicated that swimming costs increased with flow velocity (exponent = 2.36) and declined allometrically with body weight (exponent = −0.27). The newly derived swimming costs model provided a more dynamic estimate of Murray cod energy consumption, which explained 74% of variation in the swimming costs. This new model was compared to traditional bioenergetics models (fixed proportion and optimal swimming speed) to determine swimming costs in a variable temperature (6.4–26.1 °C) and flow velocity (0.06–0.46 m s−1) regime downstream of a large hypolimnetic-releasing impoundment on a major Australian river. Incorporating species-specific swimming cost models, such as the one developed here, into bioenergetics modelling allows the exploration of the impact of flow velocity in lotic systems on the growth responses of freshwater fish.

One of the most severe impacts of urbanization on aquatic systems is the increasing presence of low oxygen environments caused by anthropogenic sources of pollution. As urbanization increases nationally and globally, it is becoming exceedingly important to understand how hypoxia affects aquatic fauna, especially fish species. In an effort to better understand the impacts of prolonged hypoxia on fishes, largemouth bass were held at 3.0 and 9.0 mg L−1 for 50 days, which has previously shown to be temporally sufficient to impart plastic phenotypic changes. Following the holding period, fish from each group were subjected to a low dissolved oxygen (DO) challenge of 2.0 mg L−1 for 6 h, and their physiological and hematological parameters were compared with control fish held for 6 h with no change in DO. There were no differences in the physiological stress responses between the two holding groups; however, the low oxygen holding group had increased hemoglobin and hematocrit levels following the 6-h low oxygen challenge compared with the high oxygen group. These results suggest largemouth bass exposed to chronic low oxygen conditions, either naturally or anthropogenically, may possess a beneficial advantage of increased oxygen uptake capacity during periods of low oxygen.

Competition is a ubiquitous structuring force across systems, but different fields emphasize the role of different types of competition. In benthic marine environments, where some of the classic examples of competition were described, there is a strong emphasis on interference competition: marine invertebrates are assumed to compete fiercely for the limiting resource of space. Much of our understanding of the dynamics of this system is based on this assumption, yet empirical studies often find that increases in density can reduce performance despite free space being available. Furthermore, the assumption that space is the exclusively limiting resource raises paradoxes regarding species coexistence in this system. Here, we measure the availability of oxygen in the field and in the laboratory, as well as the tolerance of resident species to low‐oxygen conditions. We show that oxygen can be the primary limiting resource in some instances, and that exploitative competition for this resource is very likely among benthic marine invertebrates. Furthermore, growth form (and the associated risk of oxygen limitation) covaries with the ability to withstand oxygen‐poor conditions across a wide range of taxa. Oxygen availability at very small scales may influence the distribution and abundance of sessile marine invertebrates more than is currently appreciated. Furthermore, competition for multiple resources (space and oxygen) and trade‐offs in competitive ability for each may promote coexistence in this system.

The current study investigates whether it is possible to increase the meat content of captive male king crab (Paralithodes camtschaticus) (average = 2.2 kg) by feeding manufactured diets at different temperatures (4°C, 8°C and 12°C). A 110 days trial was undertaken with groups of male king crabs held in 12 land-based holding tanks. All crabs survival in the lowest temperature treatment, one animal died in the medium-temperature group (8°C) and four animals in the highest temperature treatment (12°C). The results showed that feed intake increased with increasing temperature from an average of 1.0 g kg−1 day−1 at 4°C to 2.8 g kg−1 day−1 crab at 12°C. The percentage meat content was significantly higher at the final census (60.0%) compared with the initial census (37.5%) in all temperature groups, but there were no significant differences in the percentage meat content of the king crabs held in the different temperature treatments at the conclusion of the experiment. Oxygen consumption was also significantly affected by temperature and increased with increasing temperature. The results of the experiment show that the optimal temperature to maintain, and enhance, the meat content of king crab is close to 4°C.

Some Atlantic cod in the Bornholm Basin undertake vertical foraging migrations into severely hypoxic bottom water. Hypoxic conditions can reduce the postprandial increase in gastrointestinal blood flow (GBF). This could subsequently postpone or reduce the postprandial increase in oxygen consumption (MO2), i.e. the SDA, leading to a disturbed digestion. Additionally, a restricted oxygen uptake could result in an oxygen debt that needs to be compensated for upon return to normoxic waters and this may also affect the ability to process the food. Long-term cardio-respiratory measurements were made on fed G. morhua in order to understand how the cardio-respiratory system of feeding fish respond to a period of hypoxia and a subsequent return to normoxia. These were exposed to 35% water oxygen saturation for 90 minutes, equivalent to the time and oxygen level cod voluntarily endure when searching for food in the Bornholm Basin. We found that i) gastric and intestinal blood flows, cardiac output and MO2 increased after feeding, ii) gastric and intestinal blood flows were spared in hypoxia, and iii) there were no indications of an oxygen debt at the end of the hypoxic period. The magnitude and time course of the measured variables are similar to values obtained from fish not exposed to the hypoxic period. In conclusion, when cod in the field search for and ingest prey under moderate hypoxic conditions they appear to stay within safe limits of oxygen availability as we saw no indications of an oxygen debt, or negative influence on digestive capacity, when simulating field observations.

Oceanic CO(2) has increased from 280 to 380 μatm since preindustrial times and is expected to reach 1,900 μatm by 2300. In addition, regional upwelling zones exhibit levels up to 2,300 μatm, making exploration at future global projected CO(2) levels ecologically relevant today. Recent work has demonstrated that CO(2) exposure as low as 1,000 μatm induces acidosis in toadfish (Opansus beta), leading to metabolic compensation by retention of blood HCO(3) in an effort to defend pH. Since increased serosal HCO(3) translates to increased HCO(3) rates in isolated intestinal tissue, we predicted that blood elevation of HCO(3) and Pco(2) during exposure to 1,900 μatm CO(2) would increase in vivo base secretion rates. Rectal fluid and CaCO(3) excretions were collected from toadfish exposed to 380 (control) and 1,900 μatm CO(2) for 72 h. Fluids were analyzed for pH, osmolality, ionic composition, and total CO(2). Precipitated CaCO(3) was analyzed for titratable alkalinity, Mg(2+), and Ca(2+) content. Fish exposed to 1,900 μatm CO(2) exhibited higher rectal base excretion rates, higher rectal fluid HCO(3) (mmol L(-1)), and lower fluid Cl(-) (mmol L(-1)) than controls, suggesting increased intestinal anion exchange as a result of the compensated respiratory acidosis. This study verifies that imminent projected CO(2) levels expected by the year 2300 lead to greater intestinal HCO(3) loss, a process that acts against compensation for a CO(2)-induced acidosis.

To quantify the tolerance of summer flounder Paralichthys dentatus to episodic hypoxia, resting metabolic rate, oxygen extraction, gill ventilation and heart rate were measured during acute progressive hypoxia at the fish's acclimation temperature (22° C) and after an acute temperature increase (to 30° C). Mean ± s.e. critical oxygen levels ( i.e. the oxygen levels below which fish could not maintain aerobic metabolism) increased significantly from 27 ± 2% saturation (2·0 ± 0·1 mg O 2 l −1 ) at 22° C to 39 ± 2% saturation (2·4 ± 0·1 mg O 2 l −1 ) at 30° C. Gill ventilation and oxygen extraction changed immediately with the onset of hypoxia at both temperatures. The fractional increase in gill ventilation (from normoxia to the lowest oxygen level tested) was much larger at 22° C (6·4‐fold) than at 30° C (2·7‐fold). In contrast, the fractional decrease in oxygen extraction (from normoxia to the lowest oxygen levels tested) was similar at 22° C (1·7‐fold) and 30° C (1·5‐fold), and clearly smaller than the fractional changes in gill ventilation. In contrast to the almost immediate effects of hypoxia on respiration, bradycardia was not observed until 20 and 30% oxygen saturation at 22 and 30° C, respectively. Bradycardia was, therefore, not observed until below critical oxygen levels. The critical oxygen levels at both temperatures were near or immediately below the accepted 2·3 mg O 2 l −1 hypoxia threshold for survival, but the increase in the critical oxygen level at 30° C suggests a lower tolerance to hypoxia after an acute increase in temperature.

It was hypothesized that chronic hypoxia acclimation (preconditioning) would alter the behavioural low O2 avoidance strategy of fish as a result of both aerobic and anaerobic physiological adaptations. Avoidance and physiological responses of juvenile snapper (Pagrus auratus) were therefore investigated following a 6 week period of moderate hypoxia exposure (10.2-12.1 kPa PO2, 21 ± 1°C) and compared to those of normoxic controls (PO2= 20-21 kPa, 21 ± 1°C). The critical oxygen pressure (i.e. Pcrit) limit of both groups was unchanged at ~7 kPa, as were standard, routine and maximum metabolic rates. However, hypoxia acclimated fish showed increased tolerances to hypoxia in behavioral choice chambers by avoiding lower PO2 levels (3.3 ± 0.7 vs 5.3 ± 1.1 kPa) without displaying greater perturbations of lactate or glucose. This behavioural change was associated with unexpected physiological adjustments. For example, a decrease in blood O2 carrying capacity was observed after hypoxia-acclimation. Also unexpected was an increase in whole blood P50 following acclimation to low O2, perhaps facilitating Hb-O2 off-loading to tissues. In addition, cardiac mitochondria measured in situ using permeabilised fibres showed improved O2 uptake efficiencies. The proportion of the anaerobic enzyme lactate dehydrogenase (LDH), at least relative to the aerobic marker enzyme citrate synthase (CS), also increased in heart and skeletal red muscle indicating enhanced anaerobic potential, or in situ lactate metabolism, in these tissues. Overall these data suggest that a prioritization of O2 delivery and O2 utilization over O2 uptake during long-term hypoxia may convey a significant survival benefit to snapper in terms of behavioural low O2 tolerance.

The oceanic carbonate system is changing rapidly due to rising atmospheric CO2, with current levels expected to rise to between 750 and 1,000 μatm by 2100, and over 1,900 μatm by year 2300. The effects of elevated CO2 on marine calcifying organisms have been extensively studied; however, effects of imminent CO2 levels on teleost acid–base and respiratory physiology have yet to be examined. Examination of these physiological processes, using a paired experimental design, showed that 24 h exposure to 1,000 and 1,900 μatm CO2 resulted in a characteristic compensated respiratory acidosis response in the gulf toadfish (Opsanus beta). Time course experiments showed the onset of acidosis occurred after 15 min of exposure to 1,900 and 1,000 μatm CO2, with full compensation by 2 and 4 h, respectively. 1,900-μatm exposure also resulted in significantly increased intracellular white muscle pH after 24 h. No effect of 1,900 μatm was observed on branchial acid flux; however, exposure to hypercapnia and HCO3 − free seawater compromised compensation. This suggests branchial HCO3 − uptake rather than acid extrusion is part of the compensatory response to low-level hypercapnia. Exposure to 1,900 μatm resulted in downregulation in branchial carbonic anhydrase and slc4a2 expression, as well as decreased Na+/K+ ATPase activity after 24 h of exposure. Infusion of bovine carbonic anhydrase had no effect on blood acid–base status during 1,900 μatm exposures, but eliminated the respiratory impacts of 1,000 μatm CO2. The results of the current study clearly show that predicted near-future CO2 levels impact respiratory gas transport and acid–base balance. While the full physiological impacts of increased blood HCO3 − are not known, it seems likely that chronically elevated blood HCO3 − levels could compromise several physiological systems and furthermore may explain recent reports of increased otolith growth during exposure to elevated CO2.

Greenland halibut (Reinhardtius hippoglossoides), especially juveniles, are frequently found in severely hypoxic areas (18%–25% saturation) of the St. Lawrence Estuary. We investigated the tolerance of this species to hypoxia and evaluated the consequences of low oxygen levels on metabolic capacity. At 5 °C, juveniles had a higher critical oxygen threshold than adults (15% versus 11% saturation), indicating that they were less tolerant to hypoxia. Severe hypoxia (19% saturation) did not affect the juveniles' standard metabolic rate but significantly reduced (by 55%) their maximum metabolic rate compared with normoxia. Consequently, the aerobic scope was reduced by 72% in hypoxia compared with normoxia. In juveniles, severe hypoxia increased the duration of digestive processes. The decrease in aerobic scope in hypoxia and the determination of critical oxygen threshold at a saturation level close to actual field dissolved oxygen values strongly suggest that juveniles from the St. Lawrence Estuary are living at the edge of their metabolic capacity. Consequently, the growth and distribution of Greenland halibut could be affected if there are further declines in dissolved oxygen availability.

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 3:65-79 (2012) - DOI: https://doi.org/10.3354/aei00050 Effects of a commercial, suspended eastern oyster nursery upon nutrient and sediment chemistry in a temperate, coastal embayment Shannon L. Meseck1,*, Yaqin Li1, Mark S. Dixon1, Karen Rivara2, Gary H. Wikfors1, George Luther III3 1NOAA/NMFS, 212 Rogers Avenue, Milford, Connecticut 06418, USA 2Aeros Cultured Oyster Company, 10273 N Bayview Road, Southold, New York 11971, USA 3University of Delaware, College of Marine Studies, 700 Pilottown Road, Lewes, Delaware 19958, USA *Email: shannon.meseck@noaa.gov ABSTRACT: We explored chemical effects of a commercial Floating-Upwelling-System (FLUPSY) stocked with juvenile oysters Crassostrea virginica in a small embayment. Water from the FLUPSY outflow was analyzed for nutrients (total ammonia, nitrate+nitrite, phosphate, and silicate), total suspended material (TSM), chlorophyll (chl) a, and particulate organic carbon and nitrogen (C:N). The output from the FLUPSY was compared to estuarine transects in the Bay to determine if any outputs from the FLUPSY could be detected within the embayment. Sediment samples taken near the FLUPSY and throughout the embayment were analyzed for fluxes of total ammonia, hydrogen sulfide, and oxygen. Dissolved nutrient concentrations in the FLUPSY output were no higher than in the rest of the embayment. There were, however, elevated concentrations of TSM and chl a near the FLUPSY compared to other sites in the embayment. Furthermore, suspended organic matter near the FLUPSY had a C:N ratio near the Redfield ratio, while the rest of the embayment had an elevated C:N ratio indicative of phytoplankton nitrogen limitation. These findings suggest that nutrient recycling by microbes may have been occurring in the vicinity of the FLUPSY. Sediment data showed no difference in fluxes of oxygen, hydrogen sulfide, or total ammonia between the FLUPSY output and elsewhere in the embayment. These findings suggest that the FLUPSY had very minimal effects on the chemical ecology of the embayment. KEY WORDS: Aquaculture · Sediments · Nutrients · Phytoplankton · Oysters Full text in pdf format PreviousNextCite this article as: Meseck SL, Li Y, Dixon MS, Rivara K, Wikfors GH, Luther G III (2012) Effects of a commercial, suspended eastern oyster nursery upon nutrient and sediment chemistry in a temperate, coastal embayment. Aquacult Environ Interact 3:65-79. https://doi.org/10.3354/aei00050 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 3, No. 1. Online publication date: December 19, 2012 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2012 Inter-Research.

In my thesis I investigate the ecology of maternal influences: the unique ability of mothers to influence, via genetic and non-genetic means, the phenotypic expression of their offspring. My research is presented as a series of standalone chapters that are introduced and then summarised by a general introduction (Chapter 1) and a general discussion (Chapter 6) respectively. One of the main components of an organism’s energy budget is its baseline level of energy metabolism. Individual differences in this cost of self-maintenance (termed in this chapter, resting metabolic rate, RMR) are substantial, but the causes and consequences of this variation are obscure. In Chapter 2, I review the published literature and show that maternal influences (along with other factors) can contribute substantially to variation in offspring RMR. Also, the RMR - fitness relationship appears to be modulated by environmental conditions (e.g. food supply), suggesting that the fitness consequences of a given RMR may be context-dependent. Thus, I propose that broad-scale variation in RMR might persist in natural populations, due to both spatial and temporal variation in environmental conditions and the trans-generational influence of mothers. To further investigate maternal influences on offspring energy metabolism, I measured the standard metabolic rate (SMR, a measure equivalent to RMR but used in reference to ectothermic animals) of juvenile brown trout (Salmo trutta) in response to intra-clutch manipulations of egg cortisol and testosterone (Chapter 3). Although, neither hormone affected offspring SMR (egg testosterone treatment resulted in a likely pharmacological dose), juveniles from cortisol-treated eggs were smaller and subordinate to individuals from control eggs. This indicates that variation in the amount of cortisol deposited in eggs by females, either among clutches or within them, is likely to affect juvenile performance. In a separate experiment (Chapter 4), I investigated if within-clutch differences in the phenotypes of juvenile brown trout were systematically related to the position where each individual developed during oogenesis. For a given egg size, siblings from dominant mothers were initially larger (but had a lower mass-corrected SMR) if they developed in the rear of the egg mass. However, heterogeneity in the size of siblings from different positions in the egg mass diminished in lower ranking females. Juvenile social status also varied according to egg mass position, although the direction of this effect depended on their age. Maternal influences on offspring are not only determined by conditions experienced by females immediately prior to reproduction. In Chapter 5, I investigated whether the juvenile growth rate and adult reproductive traits of female wild Atlantic salmon are related to the performance of their offspring in the wild. Investment in egg size was linked to both the juvenile and adult phenotypes of mothers. Even when controlling for egg size, the influence of these ‘past’ and ‘present’ maternal traits extended to offspring performance. Offspring growth was positively related to maternal investment in reproduction and the juvenile growth rate of each mother. The survival and biomass of offspring were also linked to adult reproductive traits but these relationships differed for mothers that had grown at either fast or slow rates as juveniles. Overall my thesis demonstrates that maternal influences are a substantial source of variation in offspring size, behaviour and physiology, both among and within clutches. My research also underlines the importance of maternal influences for offspring ecology and therefore maternal fitness.

Differences in behavioral responses to environmental conditions and biological interactions are a key determinant of individual performance. This study investigated how the availability and predictability of food resources modulates the growth of animals that adopt different behavioral strategies. Results show that, irrespective of the feeding regime, the growth of juvenile brown trout increased with the expression of active foraging behavior and, similarly, with increasing use of shelter. Conversely, territorial aggressive behavior only promoted growth when food resources were spatially and temporally predictable, and only for individuals that had high metabolic rates (when compared with their low metabolic rate siblings). Thus, this study shows that only certain behaviors are associated with variation in the physiology of individuals. Moreover, only certain behaviors associate differently with growth under different environmental conditions. These results are partially consistent with the hypothesis that environmental variability promotes the coexistence of alternative behavioral phenotypes. However, some behaviors enhanced growth irrespective of feeding regime, and we did not identify a set of conditions where fish with low resting metabolic rate (RMR) outperformed their high RMR siblings. Hence, additional layers of environmental variation are likely to be required for individuals with low RMR to show maximal growth performance.

Understanding the interplay among the external environment, physiology and adaptive behaviour is crucial for understanding how animals survive in their natural environments. The external environment can have wide ranging effects on the physiology of animals, while behaviour determines which environments are encountered. Here, we identified changes in the behavioural selection of external salinity in Fundulus heteroclitus, an estuarine teleost, as a consequence of digesting a meal. Fish that consumed high levels of dietary calcium exhibited a higher preferred salinity compared with unfed fish, an effect that was exaggerated by elevated dietary sodium chloride. The mean swimming speed (calculated as a proxy of activity level) was not affected by consuming a diet of any type. Constraining fish to water of 22 p.p.t. salinity during the digestion of a meal did not alter the amount of calcium that was absorbed across the intestine. However, when denied the capacity to increase their surrounding salinity, the compromised ability to excrete calcium to the water resulted in significantly elevated plasma calcium levels, a potentially hazardous physiological consequence. This study is the first to show that fish behaviourally exploit their surroundings to enhance their ionoregulation during digestion, and to pinpoint the novel role of dietary calcium and sodium in shaping this behaviour. We conclude that in order to resolve physiological disturbances in ion balance created by digestion, fish actively sense and select the environment they inhabit. Ultimately, this may result in transient diet-dependent alteration of the ecological niches occupied by fishes, with broad implications for both physiology and ecology.

Vertebrate embryos pass through a period of morphological similarity, the phylotypic period. Since Haeckel's biogenetic law of recapitulation, proximate and ultimate evolutionary causes of such similarity of embryos were discussed. We test predictions about changes in phenotypic and genetic variances that were derived from three hypotheses about the evolutionary origin of the phylotypic stage, i.e. random, epigenetic effects, and stabilizing selection. The random hypothesis predicts increasing values for phenotypic variances and stable or increasing values for genetic variances; the epigenetic effects hypothesis predicts declining values for phenotypic variances but stable or increasing values of genetic variances, and the stabilizing selection predicts stable phenotypic variances but decreasing genetic variances. We studied zebrafish as a model species, because it can be bred in large numbers as necessary for a quantitative genetics breeding design. A half‐sib breeding scheme provided estimates of additive genetic variances from 11 embryonic characters from 12 through to 24 hr after fertilization, i.e. before, during (15–19 hr), and after the phylotypic period. Because additive genetic variances are size dependent, we calculated narrow‐sense heritabilities as a size independent gauge of genetic contributions to the phenotype. The results show declining phenotypic variances and stable heritabilities. In conclusion, we reject the random and the stabilizing selection hypotheses and favor ideas about epigenetic effects that constrain the early embryonic development. Additive genetic variance during the phylotypic stage makes it accessible for evolution, thus explaining in a simple and straightforward way why the phylotypic period differs among vertebrates in timing, duration, and morphologies. J. Exp. Zool. (Mol. Dev. Evol.) 316:319–329, 2011. © 2011 Wiley‐Liss, Inc.

During a generalized acidosis in rainbow trout, catecholamines are released into the blood, activating red blood cell (RBC) Na+/H+ exchange (βNHE), thus protecting RBC intracellular pH (pHi) and subsequent O2 binding at the gill. Because of the presence of a Root effect (a reduction in oxygen carrying capacity of the blood with a reduction in pH), the latter could otherwise be impaired. However, plasma-accessible carbonic anhydrase (CA) at the tissues (and absence at the gills) may result in selective short-circuiting of RBC βNHE pH regulation. This would acidify the RBCs and greatly enhance O2 delivery by exploitation of the combined Bohr-Root effect, a mechanism not previously proposed. As proof-of-principle, an in vitro closed system was developed to continuously monitor extracellular pH (pHe) and O2 tension (PO2) of rainbow trout blood. In this closed system, adding CA to acidified, adrenergically stimulated RBCs short-circuited βNHE pH regulation, resulting in an increase in PO2 by >30 mmHg, depending on the starting Hb-O2 saturation and degree of initial acidification. Interestingly, in the absence of adrenergic stimulation, addition of CA still elevated PO2, albeit to a lesser extent, a response that was absent during general NHE inhibition. If plasma-accessible CA-mediated short-circuiting is operational in vivo, the combined Bohr-Root effect system unique to teleost fishes could markedly enhance tissue O2 delivery far in excess of that in vertebrates possessing a Bohr effect alone and may lead to insights about the early evolution of the Root effect.

Gymnotiform weakly electric fishes generate electric organ discharges (EODs) and sense perturbations of the resulting electric field for purposes of orientation, prey detection and communication. Some species produce oscillatory (‘wave-type’) EODs at very high frequencies (up to 2 kHz) that have been proposed to be energetically expensive. If high-frequency EODs are expensive, then fish may modulate their EOD frequency and/or amplitude in response to low-oxygen (hypoxic) stress and/or compensate for costs of signalling through other adaptations that maximize oxygen uptake efficiency. To test for evidence of an energetic cost of signalling, we recorded EOD in conjunction with metabolic rates, critical oxygen tension and aquatic surface respiration (ASR90) thresholds in Apteronotus leptorhynchus, a species found in high-oxygen habitats, and Eigenmannia virescens, a species more typically found in low-oxygen waters. Eigenmannia virescens had a lower mean ASR90 threshold and critical oxygen tension compared with A. leptorhynchus, consistent with field distributions. Within each species, there was no evidence for a relationship between metabolic rate and either EOD frequency or amplitude under normoxia, suggesting that there is no significant direct metabolic cost associated with producing a higher frequency EOD. However, when exposed to progressive hypoxia, fish generally responded by reducing EOD amplitude, which may reduce energetic costs. The threshold at which fish reduced EOD amplitude tended to be lower in E. virescens, a pattern consistent with higher tolerance to hypoxic stress. The results of this study suggest that wave-type fish reduce their EOD amplitude to reduce direct energetic costs without reducing metabolic rate under hypoxia.

Social status can vary considerably among individuals and has significant implications for performance. In addition to a genetic component, social status may be influenced by environmental factors including maternal effects such as prenatal hormone exposure. Maternal effects on traits determining social status have previously been examined in species where mothers provide parental care for relatively few offspring and therefore directly influence postnatal development. However, the generality of conclusions arising from these investigations is unclear because species that employ different reproductive strategies have not been studied. We investigated the hypothesis that egg steroid hormone levels influence the social status of juvenile brown trout ( Salmo trutta ). We manipulated intra‐clutch levels of cortisol and testosterone in eggs from 15 mothers using dilute hormone baths at the time of fertilization and examined their effects on traits that correlate with social status in juveniles [including standard body size, aggression, competitive ability and standard metabolic rate (SMR)]. Hormone treatment did not affect whole‐animal or mass‐corrected SMR at the critical developmental stage when juveniles switch from reliance on a maternally provisioned yolk sac to independent feeding. However, juveniles from cortisol‐treated eggs were smaller at this developmental stage. They were also less aggressive than, and subordinate to, fish from untreated eggs in socially competitive conditions, even after correcting for the observed effect of cortisol on body size. Egg testosterone treatment resulted in a likely pharmacological or toxicological dose with subsequent effects on both body size and behaviour in independently feeding juveniles. Results from this study demonstrate that variation in the amount of cortisol deposited in eggs by spawning females influences juvenile social status and performance. The effects of elevated egg cortisol in fish are similar to the actions of embryonic glucocorticoids reported in other vertebrate taxa with very different reproductive strategies, suggesting a widespread mechanism for the effects of maternal stress on offspring. Possible adaptive aspects of this relationship are discussed.

This is the first direct physiological evidence in support of the ionoregulatory hypothesis, challenging the long-held assumption that teleost gills develop initially for gas exchange. Resting unidirectional sodium (Na + ) uptake and oxygen (O 2 ) uptake across the skin and gills were measured simultaneously in larval rainbow trout, Oncorhynchus mykiss, during development. In soft and hard water, Na + uptake shifted to the gills by 15 and 16 days post-hatch (dph) while O 2 uptake took 50–80% longer and shifted by 23 and 28 dph, respectively. This suggests that gills are required for ionoregulation prior to gas exchange in developing rainbow trout. The age of transition for Na + uptake, gill Na +, K + -ATPase (NKA) α-subunit protein expression and gill NKA enzyme activity were not significantly different between soft and hard water-reared groups, which suggests a lack of plasticity in gill ionoregulatory development. In rainbow trout, the gills assume a dominant role in ionoregulation before gas exchange, suggesting that ionoregulation may be the initial driving force for gill development. Further investigation is required to determine whether this pattern is consistent with other teleosts and more basal fishes during early development to gain insight into the role of ionoregulation in vertebrate gill evolution.

Internal pressurization and convective gas flow, which can aerate wetland plants more efficiently than diffusion, are common in temperate species. Here, we present the first survey of convective flow in a range of tropical plants. The occurrence of pressurization and convective flow was determined in 20 common wetland plants from the Mekong Delta in Vietnam. The diel variation in pressurization in culms and the convective flow and gas composition from stubbles were examined for Eleocharis dulcis, Phragmites vallatoria and Hymenachne acutigluma, and related to light, humidity and air temperature. Nine of the 20 species studied were able to build up a static pressure of > 50 Pa, and eight species had convective flow rates higher than 1 ml min(-1). There was a clear diel variation, with higher pressures and flows during the day than during the night, when pressures and flows were close to zero. It is concluded that convective flow through shoots and rhizomes is a common mechanism for below-ground aeration of tropical wetland plants and that plants with convective flow might have a competitive advantage for growth in deep water.

Hypoxia facilitates tumor invasion and metastasis by promoting neovascularization and co-option of tumor cells in the peritumoral vasculature, leading to dissemination of tumor cells into the circulation. However, until recently, animal models and imaging technology did not enable monitoring of the early events of tumor cell invasion and dissemination in living animals. We recently developed a zebrafish metastasis model to dissect the detailed events of hypoxia-induced tumor cell invasion and metastasis in association with angiogenesis at the single-cell level. In this model, fluorescent DiI-labeled human or mouse tumor cells are implanted into the perivitelline cavity of 48-h-old zebrafish embryos, which are subsequently placed in hypoxic water for 3 d. Tumor cell invasion, metastasis and pathological angiogenesis are detected under fluorescent microscopy in the living fish. The average experimental time for this model is 7 d. Our protocol offers a remarkable opportunity to study molecular mechanisms of hypoxia-induced cancer metastasis.

Oxygen uptake ( ) and critical oxygen tension ( P crit ) were measured in resting perch Perca fluviatilis that were either fasting or digesting. Digestion caused to double (from 61 to 117 mg O 2 kg −1 h −1 ) and was associated with a rise in P crit (from 3·4 to 4·9 kPa), showing that the animal's digestive state must be considered when assessing the effect of hypoxia in natural conditions, and when defining optimal oxygen conditions in aquaculture.

We studied early embryonic development of zebra fish and tested if changes in the external raising conditions could elicit phenotypic changes during the phylotypic stage which, classically, is considered as a conserved embryonic stage. In particular, we tested for internal constraints, plasticity, and heterochrony during the early embryonic development. Our tested hypotheses predict (i) no change associated with developmental stability/internal constraints, (ii) change of the rate of development associated with developmental flexibility, and (iii) heterochronic disruption of developmental pattern associated with a modular organization of the embryo. We measured 14 traits of embryos raised in different conditions (temperature, salinity, oxygen concentration). The results of our study show that zebra fish embryos respond flexibly to changes in external parameters even during the conserved “phylotypic stage.” It also showed that internal constraints canalize early development when exposed to moderate external challenges. Hypoxic conditions, however, elicited a heterochronic delay of the onset of the development of the Anlagen of the eye and the otic vesicle from the remaining embryo. Therefore, we concluded that the eye and the otic vesicle are modules that may develop, to a certain degree, independently of the rest of the embryo. Because these modules become recognizable only under specific raising conditions, we suggest that the modularization acts as buffering mechanism against extreme developmental deviations. Our results provide support to the idea that modularity is present during the phylotypic stage, but it is not effective under normal conditions. J. Exp. Zool. (Mol. Dev. Ecol.) 314B:166–178, 2010. © 2009 Wiley‐Liss, Inc.

We investigated the ability of European sea bass (Dicentrarchus labrax) to respond simultaneously to the metabolic demands of specific dynamic action (SDA) and aerobic exercise and how this was influenced by moderate hypoxia (50% air saturation). At 3 h after feeding in normoxia at 20 degrees C, SDA raised the instantaneous oxygen uptake (Mo(2)) of sea bass by 47% +/- 18% (mean +/- SEM, N = 7) above their standard metabolic rate (SMR) when fasted. This metabolic load was sustained throughout an incremental exercise protocol until fatigue, with a 14% +/- 3% increase in their maximum aerobic metabolic rate (MMR) relative to their fasted rate. Their incremental critical swimming speed (U(crit)) did not differ between fasted and fed states. Thus, in normoxia, the bass were able to meet the combined oxygen demands of SDA and aerobic exercise. In hypoxia, the sea bass suffered a significant decline in MMR and U(crit) relative to their normoxic performance. The SDA response was similar to normoxia (84% +/- 24% above fasted SMR at 3 h after feeding), but although this load was sustained at low swimming speeds, it gradually disappeared as swimming speed increased. As a result, the hypoxic sea bass exhibited no difference in their fasted versus fed MMR. Hypoxic U(crit) did not, however, differ between fasted and fed states, indicating that the sea bass deferred their SDA to maintain exercise performance. The results demonstrate that, in normoxia, the sea bass possesses excess cardiorespiratory capacity beyond that required for maximal aerobic exercise. The excess capacity is lost when oxygen availability is limited in hypoxia, and, under these conditions, the sea bass prioritize exercise performance. Thus, environmental conditions (oxygen availability) had a significant effect on patterns of oxygen allocation in sea bass and revealed intrinsic prioritization among conflicting metabolic demands.

It is not known how the Pacific hagfish (Eptatretus stoutii) can survive extended periods of anoxia. The present study used two experimental approaches to examine energy use during and following anoxic exposure periods of different durations (6, 24 and 36 h). By measuring oxygen consumption prior to anoxic exposure, we detected a circadian rhythm, with hagfish being active during night and showing a minimum routine oxygen consumption (RMR) during the daytime. By measuring the excess post-anoxic oxygen consumption (EPAOC) after 6 and 24 h it was possible to mathematically account for RMR being maintained even though heme stores of oxygen would have been depleted by the animal’s metabolism during the first hours of anoxia. However, EPAOC after 36 h of anoxia could not account for RMR being maintained. Measurements of tissue glycogen disappearance and lactate appearance during anoxia showed that the degree of glycolysis and the timing of its activation varied among tissues. Yet, neither measurement could account for the RMR being maintained during even the 6-h anoxic period. Therefore, two independent analyses of the metabolic responses of hagfish to anoxia exposure suggest that hagfish utilize metabolic rate suppression as part of the strategy for longer-term anoxia survival.

Field observations were supplemented with laboratory experiments to reveal patterns of salinity selection and preference for grey snapper Lutjanus griseus ( c. 21 cm total length, L T ), an ecologically and economically important species in the south‐eastern U.S.A. Fish abundance data were examined from a long‐term field survey conducted in the mangrove habitats of Biscayne Bay, Florida, where salinities ranged from <1 to 40. First, regression analyses indicated significant, positive linear relationships with salinity for both L. griseus frequency of occurrence and concentration (density when present). These patterns are inconsistent with physiological expectations of minimizing energetic osmoregulatory costs. Next, the salinity preference and swimming activity of 11 L. griseus (ranging from 18 to 23 cm L T ) were investigated using a newly developed electronic shuttlebox system. In the laboratory, fish preferred intermediate salinities in the range of 9–23. Swimming activity (measured in terms of spontaneous swimming speed) followed a parabolic relationship with salinity, with reduced activity at salinity extremes perhaps reflecting compensation for higher osmoregulatory costs. It is suspected that the basis of the discrepancy between laboratory and field observations for size classes at or near maturity ultimately relates to the reproductive imperative to move towards offshore (high‐salinity) coral‐reef habitats, a necessity that probably overrides the strategy of minimizing osmoregulatory energetic costs.

Intestinal HCO3− secretion is essential to marine teleost fish osmoregulation and comprises a considerable source of base efflux attributable to both serosal HCO3− and endogenous CO2 hydration. The role of intestinal HCO3− secretion in dynamic acid—base balance regulation appears negligible in studies of unfed fish, but evidence of high intestinal fluid [HCO3−] in fed marine teleosts led us to investigate the source of this HCO3− and its potential role in offsetting the postprandial ‘alkaline tide’ commonly associated with digestion. Specifically, we hypothesized that elevated metabolic rate and thus endogenous CO2 production by intestinal tissue as well as increased transepithelial intestinal HCO3− secretion occur post-feeding and offset a postprandial alkaline tide. To test these hypotheses changes in HCO3− secretion and O2 consumption by gulf toadfish (Opsanus beta) isolated intestine were quantified 0, 3, 6, 12, 24 and 48 h post-feeding. Intestinal tissue of unfed fish in general showed high rates of HCO3− secretion (15.5 μmol g−1 h−1) and O2 consumption (8.9 μmol g−1 h−1). Furthermore, postprandial increases in both intestinal HCO3− secretion and O2 consumption (1.6- and 1.9-fold peak increases, respectively) were observed. Elevated intestinal HCO3− secretion rates preceded and outlasted those of O2 consumption, and occurred at a magnitude and duration sufficient to account for the lack of alkaline tide. The dependence of these high rates of postprandial intestinal base secretion on serosal HCO3− indicates transepithelial HCO3− transport increases disproportionately more than endogenous CO2 production. The magnitude of postprandial intestinal HCO3− secretion indicates the intestine certainly is capable of postprandial acid#x02014;base balance regulation.

Mechanistic understanding and defining novel therapeutic targets of diabetic retinopathy and age-related macular degeneration (AMD) have been hampered by a lack of appropriate adult animal models. Here we describe a simple and highly reproducible adult fli-EGFP transgenic zebrafish model to study retinal angiogenesis. The retinal vasculature in the adult zebrafish is highly organized and hypoxia-induced neovascularization occurs in a predictable area of capillary plexuses. New retinal vessels and vascular sprouts can be accurately measured and quantified. Orally active anti-VEGF agents including sunitinib and ZM323881 effectively block hypoxia-induced retinal neovascularization. Intriguingly, blockage of the Notch signaling pathway by the inhibitor DAPT under hypoxia, results in a high density of arterial sprouting in all optical arteries. The Notch suppression-induced arterial sprouting is dependent on tissue hypoxia. However, in the presence of DAPT substantial endothelial tip cell formation was detected only in optic capillary plexuses under normoxia. These findings suggest that hypoxia shifts the vascular targets of Notch inhibitors. Our findings for the first time show a clinically relevant retinal angiogenesis model in adult zebrafish, which might serve as a platform for studying mechanisms of retinal angiogenesis, for defining novel therapeutic targets, and for screening of novel antiangiogenic drugs.

Phototoxicity of polycyclic aromatic hydrocarbons (PAHs) in the Arctic is important to study since the future PAH load is likely to increase. In combination with the increased UV-light penetration due to ozone layer thinning, phototoxicity may be a potential problem for arctic areas. The aim of this study was to evaluate effects of pyrene and phototoxicity of pyrene on natural algae and bacteria from arctic sediments. Sediments from a shallow-water marine baywere spiked with different pyrene concentrations. Microcosms containing the sediment were incubated under three light regimes, natural sunlight with UV-light, natural sunlight without UV-light, and dark. Significant effects were evident at low pyrene concentrations, particularly in presence of UV-light, indicating phototoxicity. The microalgae were especially sensitive to the phototoxicity of pyrene. Already atthe lowest pyrene concentration (Cfree: 4 nM) algal 14C-incorporation and chlorophyll a content were reduced. The toxic effects of pyrene on the microalgae probably led to the release of organic matter. In agreement with this, bacterial activity increased at high pyrene concentrations indicated by increased oxygen consumption and increased release of inorganic N and P from the sediment. This study indicates that phototoxicity of PAHs may be relevant for sediment communities from shallow marine arctic areas at environmentally relevant pyrene concentrations.

Despite convincing evidence that carotenoid availability can have positive physiological effects, we still lack information on the functional consequences of carotenoid limitation at the behavioral level. Given the role carotenoids play in mitigating oxidative stress produced during physical activity and as immunostimulants, one behavioral function on which they may have a significant impact is an individual's capacity to provide parental care. We tested this hypothesis using three-spined sticklebacks ( Gasterosteus aculeatus ), a species in which males provide obligate and intensive paternal care. Males were fed either high or low (but biologically realistic) levels of carotenoids and monitored throughout incubation, during which we quantified 2 key aspects of parental care: their ability to fan their eggs under normoxic and hypoxic conditions (when both the costs and requirements of fanning increase) and their ability to defend their nest against a simulated conspecific male. High-carotenoid diet males fanned their eggs at a significantly higher rate during hypoxic (but not normoxic) conditions and had higher clutch hatching success than males fed the low-carotenoid diet. There was no evidence that they defended their nest more aggressively. Furthermore, low-carotenoid diet males also appeared to engage in cannibalization of their clutch. These results demonstrate that dietary carotenoid availability can affect a male's ability to provide parental care, and we discuss the potential mechanisms and implications of this finding.

This study reports the first results on telemetry of caudal differential pressure during spontaneous swimming activity in cod Gadus morhua and demonstrates that tail‐beat pressure may be used as a predictor of activity and swimming costs of free‐swimming cod. Tail‐beat pressure was monitored using a differential pressure sensor on the caudal peduncle of cod and spontaneous swimming activity was quantified using a customized video‐computer tracking programme. Tail‐beat pressure was found to correlate with (1) swimming speed ( U ) and oxygen consumption during forced swimming and (2) mean U during spontaneous activity. Based on the relationship between and the integrated pressure performed by the tail during forced swimming, it should be possible to predict during spontaneous activity. To gain precise measures of activity and thus predictions of for free‐swimming fish, however, individual calibrations are necessary.

Standard metabolic rate ( R s ) and critical swimming speed ( U crit ) were used to assess the aspects of physiological status (stamina) of rainbow trout Oncorhynchus mykiss. Fish were fed either 1·5% body mass daily, 1·5% body mass cyclically (3 weeks of food deprivation followed by 3 weeks of refeeding), a ration based on Stauffer’s formula (a maximum temperature‐specific ration level) daily or on Stauffer’s ration cyclically for 18 weeks. It was hypothesized that if cyclic feeding had no impact on the status of the fish, R s and U crit would not cycle with the feeding regime. This hypothesis was supported. No significant difference was found between the mean mass and the fork length of the four groups at the end of the experiment ( P > 0·05). Feeding had no effect on changes in R s among the four groups, which were significantly different throughout the experiment ( P ≤ 0·05). No significant difference in U crit was found ( P > 0·05) until at week 12 between groups fed 1·5% body mass ration cyclically and Stauffer’s ration daily ( P ≤ 0·05). For groups fed a 1·5% body mass ration cyclically and daily, significant differences occurred at week 15 ( P ≤ 0·05) but no significant difference was found by week 18 ( P > 0·05), suggesting that cyclic feeding does not affect the aspects of physiological status (stamina) of the fish.

Decreased critical swimming speed and increased oxygen consumption ( ) was found for externally tagged Atlantic cod Gadus morhua swimming at a high speed of 0·9 body length (total length, L T ) s −1. No difference was found in the standard metabolic rate, indicating that the higher for tagged cod was due to drag force rather than increased costs to keep buoyancy.