Routine Metabolic Rate Research Articles

Respiration rates of herring larvae at different salinities, and effects of previous environmental history

Metabolic rates of early life history stages of marine fishes show considerable inter-individual differences, and are highly influenced by extrinsic factors like temperature or food availability. Measuring oxygen uptake rates is a proxy for estimating metabolic rates. Still, the relationship between respiration rates and ambient or previous salinity conditions as well as parental and developmental acclimation to changes in salinity remains largely unexplored. In the present study, we conducted experiments to investigate the effects of salinity on the routine metabolic rates (RMR) of euryhaline Atlantic herringClupea harenguslarvae at 3 levels of salinity: low (6 psu), intermediate (16 psu) and high (35 psu), reflecting ecologically relevant conditions for herring populations in the Atlantic Ocean and Baltic Sea. The larvae originated from different genetic backgrounds and salinity adaptations to account for cross-generation effects on metabolic rates. Closed respirometry carried out over 24 h on individual fish larvae generally confirmed near isometric respiration rates at all salinity regimes, with rates being 15.4% higher at 6 psu and 7.5% higher at 35 psu compared to 16 psu conditions. However, transgenerational acclimation to different salinity regimes of the parents had no effect on the salinity-specific metabolic rates of their offspring. Our study demonstrates the ability of herring to cope with a wide range of salinity conditions, irrespective of parental environmental history and genetic origin. This phenotypic plasticity is considered to be one of the main contributing factors to the success of herring as a widely distributed fish species in the North Atlantic and adjacent waters.

Cold temperature tolerance of the alien Indo-Pacific damselfish Neopomacentrus cyanomos from the Southern Gulf of Mexico

The abundance of the alien, Indo-Pacific damselfish Neopomacentrus cyanomos on an oil-loading platform in the southwest Gulf of Mexico indicates that widely distributed platforms could facilitate the expansion of its geographic range across the western and northern fringes of the Gulf. From there it likely will spread to other areas of the Greater Caribbean. The lionfish example demonstrates that it eventually happens, and can do so rapidly. Reduced temperature effects on the physiology of this species were examined to better predict its survivability in the northern Gulf during winter, when sea surface temperatures fall as low as 15 °C along the coast. Overall, our results show that when the degree of experimental temperature decline was large and rapid, no compensation occurred and the stress response observed mostly reflected cellular processes that minimized damage. Integrated biomarker response values were significantly different between fish rapidly exposed to colder vs. warmer temperatures (declines of −4 °C each day, from 26 to 14 °C), reflected in higher values of blood metabolites and routine metabolic rates observed in fish exposed to 14 and 18 °C respectively, and lower activity of all enzymes, lower protein carbonylation, and higher oxidative damage to lipids in fish exposed to 14 °C. While the physiological proxies responded to minimize damage during the rapid-decrease experiment, the same proxies reflected the consequences of compensation when fish were thermally challenged after a 45 days acclimation at 18 °C. In this case, lower values of blood metabolites and high antioxidant levels and indicators of damages underpinned its pejus lower range. Based on the results of the present work, it seems clear that low winter SSTs in the northern Gulf will slow down the colonization of the inshore area of N. cyanomos. We suggest that the use of physiological cellular stress markers on specimens acquired at the beginning of an invasion should be implemented in new standardized experimental protocols, including both rapid increases/decreases of temperature and post-acclimation temperature challenges, to assess the invasiveness potential of aquatic species such as this.

Cost of respiration energy in the larvae of Luciobarbus xanthopterus Heckel,1843 larvae artificially hatched in Basrah, Iraq.

Artificial breeding of the native fish Luciobarbus xanthopterus Heckel was conducted for the first time in Basrah at the Marine Science Center's hatchery (2009). We studied energy costs of the metabolic rate of the larval phase, during the period of 45 days, via the experimental laboratory measurements of the oxygen consumption rate at three temperatures 22, 26, 30 (C◦) coincided with the ambient water temperature in the rearing tanks (22.0-29.0 C◦). Direct significant (P < 0.05) positive linear correlations was estimated between time in days and both temperature (Y1) and fresh weight (Y2) of the larvae.Y1 = 0.0804 X +22.922 , R2 0.77, P < 0.05Y2 = 1.2783 X -4.985 , R2 0.90, P < 0.05The rate of oxygen consumption varied from 0.799 mg O2/ ind./d of the mass group (9.58) at 22 C◦, to 39. 36 mg O2 / ind./d of the mass group (35.0 mg) at 26 C◦, and declined to 29.16 mg O2/ ind./d of the mass group (35.0 mg) at 30 C◦, and the mass specific O2 consumption rate (metabolic rate M) varied from 3.170 mg O2/mg/d. to 1.121 mg O2/ mg/d and declined to 0.8304 mg O2/mg/d for the three groups respectively. The energy cost as estimated in cal./mg/d were varied from 2.27 for the period 1-5 days of their life to 1.056 cal./mg/d at the period 40-45 days of their life, and the daily energy costs of one larva was varied from 9.012 cal. during (1-5 days) to 43.041 cal. during days 35-40 of their life, the estimated values represent the routine metabolic rate level (RMR).

Multiple Stressors in the Environment: The Effects of Exposure to an Antidepressant (Venlafaxine) and Increased Temperature on Zebrafish Metabolism.

Aquatic organisms are continuously exposed to multiple environmental stressors working cumulatively to alter ecosystems. Wastewater-dominated environments are often riddled by a myriad of stressors, such as chemical and thermal stressors. The objective of this study was to examine the effects of an environmentally relevant concentration of a commonly prescribed antidepressant, venlafaxine (VFX) [1.0 μg/L], in addition to a 5°C increase in water temperature on zebrafish metabolism. Fish were chronically exposed (21 days) to one of four conditions: (i) 0 μg/L VFX at 27°C; (ii) 1.0 μg/L VFX at 27°C; (iii) 0 μg/L VFX at 32°C; (iv) 1.0 μg/L VFX at 32°C. Following exposure, whole-body metabolism was assessed by routine metabolic rate (RMR) measurements, whereas tissue-specific metabolism was assessed by measuring the activities of major metabolic enzymes in addition to glucose levels in muscle. RMR was significantly higher in the multi-stressed group relative to Control. The combination of both stressors resulted in elevated pyruvate kinase activity and glucose levels, while lipid metabolism was depressed, as measured by 3-hydroxyacyl CoA dehydrogenase activity. Citrate synthase activity increased with the onset of temperature, but only in the group treatment without VFX. Catalase activity was also elevated with the onset of the temperature stressor, however, that was not the case for the multi-stressed group, potentially indicating a deleterious effect of VFX on the anti-oxidant defense mechanism. The results of this study highlight the importance of multiple-stressor research, as it able to further bridge the gap between field and laboratory studies, as well as have the potential of yielding surprising results that may have not been predicted using a conventional single-stressor approach.

The effect of normoxia exposure on hypoxia tolerance and sensory sampling in a swamp-dwelling mormyrid fish

Effects of energetic limitations on the performance of sensory systems are generally difficult to quantify. Weakly electric fishes provide an ideal model system to quantify the effects of metabolic stressors on sensory information acquisition, because they use an active-sensing strategy that permits easy measurement of the sensing effort. These fishes discharge an electric signal and sense perturbations of the resulting electric field. We used the mormyrid Petrocephalus degeni to quantify the relationship between routine metabolic rate and the rate of sensory sampling (rate of electric organ discharge, EOD) while under progressive hypoxia by quantifying the critical oxygen tension (PC-MR) and the critical electric organ discharge threshold (PC-EOD). PC-MR was significantly higher in fish acclimated to normoxia for over 40 days compared to animals tested within 1–5 days of capture from a hypoxic swamp, which suggests high costs of maintaining hypoxia tolerance; however, there was no acclimation effect on PC-EOD. All P. degeni reached their PC-EOD prior to their PC-MR. However, below the respective critical tension value, EOD rate decreased more gradually than the metabolic rate suggesting that the fish were increasing the proportion of their energy budget allocated to acquiring sensory information as dissolved-oxygen levels dropped. Trade-offs between sensory sampling and other physiological functions are also suggested by the increase in routine EOD rate with long-term normoxia acclimation, in contrast to metabolic rate, which showed no significant changes. These results highlight the relationship between sensory sampling and metabolic rate in response to progressive hypoxia and the plasticity of hypoxia tolerance.

Metabolic rates from Bluntnose minnow (Pimephales notatus) populations at lower latitudes are more sensitive to changes in temperature than populations at higher latitudes

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

Mitochondria, sex and variation in routine metabolic rate.

Variation in the metabolic costs associated with organismal maintenance may play a key role in determining fitness, and thus these differences among individuals are likely to be subject to natural selection. Although the evolvability of maintenance metabolism depends on its underlying genetic architecture, relatively little is known about the nature of genetic variation that underlies this trait. To address this, we measured variation in routine metabolic rate (ṀO2routine ), an index of maintenance metabolism, within and among three populations of Atlantic killifish, Fundulus heteroclitus, including a population from a region of genetic admixture between two subspecies. Polygenic association tests among individuals from the admixed population identified 54 single nucleotide polymorphisms (SNPs) that were associated with ṀO2routine , and these SNPs accounted for 43% of interindividual variation in this trait. However, genetic associations with ṀO2routine involved different SNPs if females and males were analysed separately, and there was a sex-dependent effect of mitochondrial genotype on variation in routine metabolism. These results imply that there are sex-specific genetic mechanisms, and potential mitonuclear interactions, that underlie variation in ṀO2routine . Additionally, there was evidence for epistatic interactions between 17% of the possible pairs of trait-associated SNPs, suggesting that epistatic effects on ṀO2routine are common. These data demonstrate not only that phenotypic variation in this ecologically important trait has a polygenic basis with considerable epistasis among loci, but also that these underlying genetic mechanisms, and particularly the role of mitochondrial genotype, may be sex-specific.

Prediction of Mercury Elimination Rate Coefficients of Fish is Improved by Incorporating Fish Temperature Classification into Models.

This study evaluated the dependence of mercury (Hg) elimination by fish on species specific fish metabolic rate in order to generate improved algorithms of Hg elimination rate coefficients. Mercury elimination rate coefficient observations were collected by literature review and fish routine metabolic rate (RMR) estimates calculated using the Wisconsin Fish Bioenergetics Model. Three models were compared that considered body weight, temperature, thermal category, Hg depuration period and RMR as predictors of Hg elimination. The best performing model incorporated body size, temperature and fish thermal category, explaining 79% of the variation of the calibration data and between 20% and 69% of the variation of validation data sets. The results support the conclusion that species-specific differences in metabolic rate influence mercury elimination by fish but also highlight major data gaps in the mercury toxicokinetic literature necessary to develop robust models Hg elimination by fish.

Effects of intracoelomic transmitter implantation on metabolic rate, swimming performance, growth and survival in juveniles of two salmonids.

In this study, we investigated the effects of acoustic tag implantation on standard and routine metabolic rate (SMR and RMR, estimated via oxygen consumption), critical swimming speed (Ucrit ), survival and growth in juveniles of rainbow trout Oncorhynchus mykiss and lake trout Salvelinus namaycush. Tag burdens ranged from 1.8% to 7.5% across the two species. Growth rates in acoustic-tagged fish were equal to or higher than those in other treatments. Acoustic-tagged S. namaycush had a marginally lower Ucrit than controls but that effect was not replicated in the O. mykiss experiment. Tagging did not have clear effects on metabolic rate but there was an interaction whereby SMR and RMR tended to increase with time since surgery in tagged O. mykiss but not in other treatments (the same trend did not occur in S. namaycush). Survival was high across treatments (mean 98% survival among O. mykiss, 97.5% among S. namaycush). There were no statistically significant effects of tag burden (percentage of body mass) except for a weak negative relationship with growth rate (across species) and a weak positive relationship with Ucrit but only in the O. mykiss. Collectively, our findings suggest there were minor, context-dependent effects of acoustic tagging in juvenile S. namaycush and O. mykiss during an eight-week laboratory experiment. Further research will be required to assess whether tagging can cause meaningful behavioural effects in these species in captivity or in the wild and whether there is a tag burden threshold above which deleterious effects consistently occur.

Rapid larval growth is costly for post-metamorphic thermal performance in a Great Barrier Reef fish

Most marine fish species disperse during a planktonic larval stage where individuals exhibit variation in pelagic duration, growth rate and settlement size. Extreme predation risk is predicted to select for rapid growth rates and decreased pelagic duration as a strategy for increasing survival to settlement. How larval traits affect post-metamorphic performance, however, has been a contentious topic over the past 50 yrs. Some studies suggest that larval traits have carry-over effects to later life stages, where larval traits can be positively or negatively correlated with post-metamorphic performance. For example, individuals with rapid larval growth rates may settle at larger sizes and have faster post-metamorphic locomotion than slow-growing individuals. Alternatively, trade-offs between life stages might exist, where rapid larval growth rate may be negatively correlated with post-metamorphic locomotion, potentially due to energetic resource allocation trade-offs. In addition, other studies suggest that larval traits are decoupled from later life stages to allow for a transition in morphology and habitat. We tested how Bathygobius cocosensis hatch size, larval growth rates, settlement size and pelagic duration correlated with post-metamorphic thermal performance of burst swimming speed, routine metabolic rate and critical thermal maximum. We found that larval growth rate was negatively correlated with juvenile routine metabolic rate and burst swimming speed across a range of test temperatures. That is, fast-growing larvae had slower burst swimming speeds and lower routine metabolic rates across temperature as juveniles compared to slower-growing larvae. We also found that hatch size and pelagic larval duration were not correlated with post-metamorphic performance. Thus, we provide evidence both for larval traits having carry-over effects on later life stages and also for larval traits being decoupled with thermal performance post-metamorphosis. This is the first study to show that rapid larval growth rate is costly for post-metamorphic thermal performance.

Salp metabolism: temperature and oxygen partial pressure effect on the physiology of Salpa fusiformis from the California Current

AbstractSalps are pelagic tunicates that play an important role in carbon cycling by filter feeding and packaging waste into dense fecal pellets that sink rapidly to the deep ocean. There has been limited research on salp physiology and no studies that examine how changes in environmental factors such as temperature and dissolved oxygen impact basic physiological processes. Here I examine temperature and oxygen partial pressure effect on metabolism in blastozooids of Salpa fusiformis. Routine metabolic rates of 1.66 and 3.95 μmol O2 g−1 h−1 wet weight at 10°C and 17°C, respectively, resulted in a Q10 = 3.45. The observed decrease in metabolism associated with decreased temperature, as well as hypoxia tolerance, is explored in the context of observed vertical migrations into hypoxic waters in the California Current, and potential impacts on carbon output. Metabolic rates for S. fusiformis are compared to metabolic rates published for other species of salps and gelatinous zooplankton. Expansion of this work across a broader set of species is critical to quantify the impact climate change may have on salps and their role in marine carbon cycling.

Effect of protein synthesis inhibitor cycloheximide on starvation, fasting and feeding oxygen consumption in juvenile spiny lobster Sagmariasus verreauxi.

Metabolism in aquatic ectotherms evaluated by oxygen consumption rates reflects energetic costs including those associated with protein synthesis. Metabolism is influenced by nutritional status governed by feeding, nutrient intake and quality, and time without food. However, little is understood about contribution of protein synthesis to crustacean energy metabolism. This study is the first using a protein synthesis inhibitor cycloheximide to research contribution of cycloheximide-sensitive protein synthesis to decapod crustacean metabolism. Juvenile Sagmariasus verreauxi were subject to five treatments: 2-day fasted lobsters sham injected with saline; 2-day fasted lobsters injected with cycloheximide; 10-day starved lobsters injected with cycloheximide; post-prandial lobsters fed with squid Nototodarus sloanii with no further treatment; and post-prandial lobsters injected with cycloheximide. Standard and routine metabolic rates in starved lobsters were reduced by 32% and 41%, respectively, compared to fasted lobsters, demonstrating metabolic downregulation with starvation. Oxygen consumption rates of fasted and starved lobsters following cycloheximide injection were reduced by 29% and 13%, respectively, demonstrating protein synthesis represents only a minor component of energy metabolism in unfed lobsters. Oxygen consumption rate of fed lobsters was reduced by 96% following cycloheximide injection, demonstrating protein synthesis in decapods contributes a major proportion of specific dynamic action (SDA). SDA in decapods is predominantly a post-absorptive process likely related to somatic growth. This work extends previously limited knowledge on contribution of protein synthesis to crustacean metabolism, which is crucial to explore the relationship between nutritional status and diet quality and how this will affect growth potential in aquaculture species.

Is individual variation in metabolic rate related to growth of spiny lobster in culture and what is the influence of social interaction?

Research with a variety of aquatic ectotherms suggests that variation in individual metabolic rate (i.e., metabolic phenotype) can be a factor that influences the behaviour and growth of individuals. Slow growth, growth disparity and growth depensation have been reported as major drawbacks to spiny lobster production which is thought to be associated with agonistic behaviour of dominant individuals controlling a disproportional share of food resources. Our study examined the relationship between individual variation of metabolic phenotypes (standard, routine and active metabolic rates and aerobic scope), and growth performance of juvenile spiny lobster, Sagmariasus verreauxi (5.99 ± 0.46 g) that were reared either individually (n = 20) or communally as a group of 20 for 90 days. Growth performance and feed intake were significantly higher in communal rearing demonstrating that social interaction is important for promoting growth of spiny lobsters. There was a positive relationship between standard metabolic rate, routine metabolic rate and growth in individually reared lobsters indicating a direct link between metabolic phenotype and growth of lobsters in the absence of social interaction. There was no relationship between metabolic phenotype and growth in communal rearing suggesting that social interactions outweigh the direct link between metabolic rate and lobster growth. The results demonstrate for the first time that growth performance of spiny lobsters can be linked with individual variation in metabolic status however social behaviour plays a more dominant role in determining growth of this naturally gregarious species.

Effect of temperature on critical oxygen tension (Pcrit) and gill morphology in six cyprinids in the Yangtze River, China

We evaluated the hypoxia tolerance capacities of fish in response to a range of temperatures which they often experience in aquaculture. We selected six cyprinids in the Yangtze River that were closely related in their phylogeny and widely used in the Chinese aquaculture industry as experimental animals: juvenile qing bo Spinibarbus sinensis, Chinese bream Parabramis pekinensis, grass carp Ctenopharyngodon idellus, big head carp Aristichthys nobilis, silver carp Hypophthalmichthys molitrix and common carp Cyprinus carpiovar Jian. We measured individual metabolic rate (ṀO2) and calculated the routine metabolic rate (RMR), Q10 and critical oxygen tension (Pcrit) after two weeks of acclimation at either 10, 15, 20, 25 or 30 °C. Gill morphology was also examined. A variety of Pcrit responses was observed: the Pcrit increased (qing bo), decreased (Chinese bream and grass carp) or was conserved (big head carp, silver carp and common carp) with increasing acclimation temperatures (10 - 30 °C). Apparent thermal-induced gill remodeling was found in three (grass carp, big head carp and silver carp) of the six cyprinids studied, with common carp also exhibiting some degree of gill structure modification. RMR was positively correlated with Pcrit at temperatures ranging from 10 to 30 °C in qing bo and big head carp; however, such significant correlation was not found in the remaining cyprinids, possibly due to their gill remodeling potential during thermal changes and thus an increased lamellar surface area at higher temperatures.

Polymorphism and multiple correlated characters: Do flatfish asymmetry morphs also differ in swimming performance and metabolic rate?

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

The effect of temperature acclimation on thermal tolerance, hypoxia tolerance and aerobic scope in two subspecies of sheepshead minnow; Cyprinodon variegatus variegatus and Cyprinodon variegatus hubbsi

The freshwater teleost Cyprinodon variegatus hubbsi (Cvh) diverged from its euryhaline relative Cyprinodon variegatus variegatus (Cvv) ~150 kya and these subspecies are physiologically distinct in their osmoregulatory capabilities. Cvv inhabits intertidal estuaries and saltwater marshes along the Gulf of Mexico and Atlantic coast, where they experience a broad temperature range from −1.9 to 43 °C and frequent bouts of hypoxia. In contrast, Cvh lives in several lakes in central Florida, where temperature is more stable (12–31 °C) and hypoxia is uncommon. To assess whether relaxed selective pressure on Cvh has resulted in reduced temperature and hypoxia tolerance, a comparative study on the effects of acclimation to 25, 30 and 35 °C on critical thermal tolerance (CTMax), hypoxia tolerance, and aerobic scope was performed. The CTMax was similar between subspecies and positively correlated with acclimation temperature. Neither subspecies, however, could survive at 38 °C for a prolonged period of time. In general, Cvv displayed greater hypoxia tolerance and aerobic scope relative to Cvh over the range of acclimation temperatures. Routine metabolic rate was significantly lower while maximum metabolic rate and aerobic scope were significantly higher in Cvv, but only in fish acclimated to 30 °C. Overall, the different responses of Cvh to relaxed selective pressure suggest these traits are weakly linked physiologically in these fishes.

The environmental tolerances and metabolic physiology of sablefish (Anoplopoma fimbria)

Given the potential impacts of global warming, such as increases in temperature and the frequency/severity of hypoxia in marine ecosystems, it is important to study the impacts of these environmental challenges on sea-cage reared aquaculture species. This study focuses on the sablefish (Anoplopoma fimbria), an emerging aquaculture species that has a unique ecology in the wild. For instance, adults inhabit oxygen minimum zones and cool waters at depths up to 1500 m. Using Atlantic salmon (Salmo salar) (~1132 g adults) as a comparative species, we used intermittent-flow respirometry to characterize the tolerance and metabolic response of sablefish (~10 g juveniles and ~675 g adults) to acute increases in temperature (2 °C h−1) and decreases in oxygen level (~10% air saturation h−1). Adult sablefish were much more hypoxia tolerant than adult salmon [O2 level at loss of equilibrium ~5.4% vs. ~24.2% air saturation, respectively]. In addition, sablefish could withstand upper temperatures only slightly lower than salmon [critical thermal maximum (CTmax) ~24.9 °C vs. ~26.2 °C, respectively]. Sablefish juveniles were both less hypoxia and thermally tolerant than adults [critical O2 tension ~18.9% vs. ~15.8% air saturation; CTmax ~22.7 vs. ~24.9 °C, respectively]. Interestingly, many of these differences in environmental tolerance could not be explained by differences in metabolic parameters (aerobic scope or routine metabolic rate). Our findings show that sablefish are tolerant of high temperatures, and very tolerant of hypoxia, traits that are advantageous for an aquaculture species in the era of climate change.

The effects of salinity and photoperiod on aerobic scope, hypoxia tolerance and swimming performance of coho salmon (Oncorhynchus kisutch) reared in recirculating aquaculture systems

Land-based recirculating aquaculture systems (RAS) have been used to rear salmon from smolt to market-sized adults, but high operating costs have limited their wide spread adoption. One clear advantage of using RAS for salmon aquaculture over open net pens is that fish can be reared under optimal conditions in an attempt to maximize growth and physiological performance and reduce overall production costs. However, few studies have attempted to define the optimal conditions for the long-term rearing of salmon. Thus, the goal of this study is to determine the effects of salinity and photoperiod, two factors that can be easily manipulated in RAS, on the physiological performance of coho salmon (Oncorhynchus kisutch) during long-term rearing. To address this goal, post-smolt coho salmon were reared for 150 days in replicate RAS at 2.5, 5, 10 and 30 ppt under either 12:12 and 24:0 (light:dark) photoperiods. Routine metabolic rate, maximum metabolic rate, aerobic scope and hypoxia tolerance were measured at 60 and 120 days of rearing, while swimming performance was assessed at 60 and 150 days of rearing. There were no effects of salinity or photoperiod on metabolic rate measurements, hypoxia tolerance or swimming performance at any sampling time. There were, however, significant effects of salinity and photoperiod on post-swimming hematology. The results suggest that physiological disturbances continue to manifest due to different environmental conditions, despite acclimation, but do not hinder the animal's ability to cope with physiological stressors. Overall, rearing salinity and photoperiod had very few measurable effects on the physiology and performance of coho salmon except the ionoregulatory disturbances following swimming at salinities of 2.5 and 30 ppt.

Effects of acute temperature changes on the swimming abilities and oxygen consumption ofPtychobarbus kaznakovifrom the Lancang River

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

Proactive coping style in early emerging rainbow trout carries a metabolic cost with no apparent return

The timing with which salmonid larvae emerge from their gravel nests is thought to be correlated with a particular suite of behavioural and physiological traits that correspond to the stress coping style of the individual. Among these traits, aggressiveness, dominance and resilience to stress, are potentially interesting to exploit in aquaculture production. In the present study a series of experiments were performed, with the purpose of characterising behavioural, metabolic and production related traits in rainbow trout juveniles from different emergence fractions. Newly hatched rainbow trout were sorted according to their emergence time from an artificial redd. The early, middle, and late fractions were retained and assessed for their physiological response to stress, growth performance, metabolism, fasting tolerance, and potential for compensatory growth. The early emerging fraction showed proactive behavioural traits; they were faster to reappear following startling, showed a reduced cortisol response following stress, and a reduced metabolic cost of recovery. Emergence time was not correlated with any differences in standard or maximum metabolic rates, but was however, correlated with higher routine metabolic rates, as demonstrated by significantly bigger weight losses during fasting in the early emerging group. Growth rates and feed conversion efficiencies were not significantly different when fish were co-habitated under a restrictive feeding regime, suggesting that early emerging fish are not able to monopolise food resources. The intermediate emerging group, which makes up the bulk of a population and is often ignored, appears to possess the best growth performance traits, possibly because they do not expend excessive energy on dominance behaviour such as the early emerging group, while they are also not overly timid or stress prone such as the late emerging group.