Intermittent-flow Respirometry Research Articles

Thermal performance curves for aerobic scope and specific dynamic action in a sexually dimorphic piscivore: implications for a warming climate.

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

Effects of temperature, body size, and sex on the standard metabolic rates of a sexually dimorphic freshwater piscivore, walleye (Sander vitreus)

Walleye ( Sander vitreus) are a sexually dimorphic freshwater piscivore that have long been studied using bioenergetics modeling, yet robust estimates of metabolic rates for use in those models have been lacking. Therefore, we quantified the effects of body mass, water temperature, and sex, on standard metabolic rate (SMR). We estimated SMR across temperatures ranging 0.5–24 °C using intermittent-flow respirometry for male ( n = 54) and female ( n = 53) walleye raised in hatchery conditions. We found a significant interaction between sex and temperature, whereby males had lower SMR below 16 °C, but increased such that SMR was ∼16% higher than females at 22 °C. The mass-scaling coefficient, b, was similar for both sexes at a value around 1. These estimates are the first to be generated using respirometry for adult walleye and differ slightly from those being used by previous bioenergetics models, which may have underestimated the energetic costs of SMR, and did not include sex-specific estimates for metabolism.

Capture and discard practises associated with an ornamental fishery affect the metabolic rate and aerobic capacity of three-striped dwarf cichlids Apistogramma trifasciata.

Fishing causes direct removal of individuals from wild populations but can also cause a physiological disturbance in fish that are released or discarded after capture. While sublethal physiological effects of fish capture have been well studied in commercial and recreational fisheries, this issue has been overlooked for the ornamental fish trade, where it is common to capture fish from the wild and discard non-target species. We examined metabolic responses to capture and discard procedures in the three-striped dwarf cichlid Apistogramma trifasciata, a popular Amazonian aquarium species that nonetheless may be discarded when not a target species. Individuals (n= 34) were tagged and exposed to each of four treatments designed to simulate procedures during the capture and discard process: 1) a non-handling control; 2) netting; 3) netting +30seconds of air exposure; and 4) netting +60seconds of air exposure. Metabolic rates were estimated using intermittent-flow respirometry, immediately following each treatment then throughout recovery overnight. Increasing amounts of netting and air exposure caused an acute increase in oxygen uptake and decrease in available aerobic scope. In general, recovery occurred quickly, with rapid decreases in oxygen uptake within the first 30minutes post-handling. Notably, however, male fish exposed to netting +60seconds of air exposure showed a delayed response whereby available aerobic scope was constrained <75% of maximum until ~4-6hours post-stress. Larger fish showed a greater initial increase in oxygen uptake post-stress and slower rates of recovery. The results suggest that in the period following discard, this species may experience a reduced aerobic capacity for additional behavioural/physiological responses including feeding, territory defence and predator avoidance. These results are among the first to examine impacts of discard practises in the ornamental fishery and suggest ecophysiological research can provide valuable insight towards increasing sustainable practises in this global trade.

Energetic costs of mounting an immune response in a coral reef damselfish (Pomacentrus amboinensis)

While immune responses can be energetically costly, quantifying these costs is challenging. We tested the metabolic costs of immune activation in damselfish ( Pomacentrus amboinensis Bleeker, 1868) following a mass-adjusted injection of lipopolysaccharide (LPS) endotoxin. Fish were divided into eight treatments: two controls (handling and saline injection) and six LPS groups with concentrations ranging from 3 to 100 mg kg−1. We used intermittent flow respirometry to measure differences in oxygen uptake (delta ṀO2) 20 h before versus 20 h after LPS injection and changes in metabolic traits (lowest, routine, and peak metabolic rates) as proxies of the aerobic costs of metabolism. Spleen somatic index (SSI) and gene expression in spleens were measured to assess immune activation. We found no difference in metabolic traits or SSI but observed different nonlinear patterns of delta ṀO2 in fish exposed to 50 and 100 mg kg−1 LPS compared to lower doses and controls. Fish exposed to high doses of LPS also had lower residual aerobic scope compared to controls and lower LPS doses. Fish exposed to doses of 3, 50, and 100 mg kg−1 showed altered gene expression compared to the handling control. Overall, our results suggest that immune activation has measurable effects on metabolic traits that are both dose- and time-dependent.

Comparison of metabolic rate between two genetically distinct populations of lake sturgeon.

Environmental temperatures differ across latitudes in the temperate zone, with relatively lower summer and fall temperatures in the north leading to a shorter growing season prior to winter. As an adaptive response, during early life stages, fish in northern latitudes may grow faster than their conspecifics in southern latitudes, which potentially manifests as different allometric relationships between body mass and metabolic rate. In the present study, we examined if population or year class had an effect on the variation of metabolic rate and metabolic scaling of age-0 lake sturgeon (Acipenser fulvescens) by examining these traits in both a northern (Nelson River) and a southern (Winnipeg River) population. We compiled 6 years of data that used intermittent flow respirometry to measure metabolic rate within the first year of life for developing sturgeon that were raised in the same environment at 16°C. We then used a Bayesian modeling approach to examine the impacts of population and year class on metabolic rate and mass-scaling of metabolic rate. Despite previous reports of genetic differences between populations, our results showed that there were no significant differences in standard metabolic rate, routine metabolic rate, maximum metabolic rate, and metabolic scaling between the two geographically separated populations at a temperature of 16°C. Our analysis implied that the lack of metabolic differences between populations could be due to family effects/parental contribution, or the rearing temperature used in the study. The present research provided insights for conservation and reintroduction strategies for these populations of lake sturgeon, which are endangered or threatened across most of their natural range.

Standard metabolic rate differs between rainbow trout (Oncorhynchus mykiss) growth forms

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

Seasonal and perennial water populations of an endemic crayfish differ in behavioural responses to drying but not metabolism

AbstractCrayfish perform important roles within freshwater ecosystems, including in regions where global warming is causing prolonged drying of waterbodies. However, little is known about responses of crayfish to habitat drying from both a behavioural and physiological perspective. We compared burrowing ability, survival and metabolism of the crayfish Cherax quinquecarinatus from a seasonal stream and a perennial stream. Burrowing ability and crayfish survival were quantified in a mesocosm experiment contrasting sediment type (sand vs. clay/sand mixture) and water regime. Aerobic scope, standard metabolic rate (SMR) and maximum metabolic rate (MMR) were also compared using intermittent flow respirometry. Crayfish from the seasonal stream showed limited burrowing ability but higher survival in the drying treatment, while the perennial stream crayfish burrowed strongly in the clay/sand sediment. Higher survival suggests that crayfish from seasonal streams might be physiologically better adapted to drying. Larger crayfish burrowed more proficiently, reaching the saturated hyporheic zone refuge in the clay/sand sediment treatment. SMR/MMR/aerobic scope did not differ between populations or respirometry runs; however, SMR differed between individuals, perhaps due to personality traits. There was a significant negative relationship between MMR/aerobic scope and weight. Sediment type may limit C. quinquecarinatus burrowing and persistence through drying. Crayfish populations did not differ in terms of metabolism; however, crayfish from seasonal habitats may possess more efficient physiological adaptations to drying. This study highlights the need for greater research attention on the effects of climatic drying on both the behaviour and the physiology of species exposed to climate change.

Caribbean scleractinian corals exhibit highly variable tolerances to acute hypoxia

IntroductionClimate change, and the increase in sea surface temperature, is exacerbating ocean deoxygenation because of the inherent property of seawater to sequester less dissolved gas, such as oxygen, at warmer temperatures. While most coral reef studies focus on the effects of thermal stress and ocean acidification, few studies acknowledge the threat of hypoxia. Hypoxia is traditionally defined as 6.3 kPa (2 mg L-1 O2), however, a universal hypoxia threshold is not useful given the vast range of responses among marine organisms. The range of metabolic responses and tolerances to hypoxia are unknown for Caribbean coral species and their algal symbionts.ObjectiveHere, we quantified the spectrum of acute hypoxia tolerances and the range of metabolic responses of six ecologically and structurally important Caribbean coral species (Acropora cervicornis, Siderastrea radians, Siderastrea siderea, Porites astreoides, Porites porites, and Orbicella faveolata) and their algal symbionts (Symbiodinium, Breviolum, and Durusdinium spp.).MethodsA total of 24 coral fragments (4 individuals per species) were exposed to 10 distinct oxygen concentrations ranging from normoxia (20.38 kPa) to severe hypoxia (3.3 kPa). We used intermittent flow respirometry to measure coral host respiration in the dark and algal symbiont photosynthesis in the light at each oxygen level. We determined a line of best fit for the metabolic rate vs. PO2 data and calculated the critical oxygen partial pressure (PO2 crit), a method that has not been tested on symbiotic species.ResultsCoral species and their algal symbionts measured here displayed a wide range of hypoxia tolerances. For the coral hosts, PO2 crit values differed roughly two-fold ranging from 5.74 kPa to 16.93 kPa, and for the algal symbionts, PO2 crit values differed roughly three-fold ranging from 3.9 kPa to 11.3 kPa.DiscussionThese results should be regarded as a first step to characterizing the metabolic response and acute tolerance of multiple coral hosts and algal symbionts to a wide range of oxygen concentrations. Given that some PO2 crit values were above the generally accepted hypoxia threshold, these results have implications for the community composition of reefs under a rapidly changing climate and can guide purposeful reef restoration.

Thermal preference does not align with optimal temperature for aerobic scope in zebrafish (Danio rerio).

Warming is predicted to have negative consequences for fishes by causing a mismatch between oxygen demand and supply, and a consequent reduction in aerobic scope (AS) and performance. This oxygen and capacity limited thermal tolerance (OCLTT) hypothesis features prominently in the literature but remains controversial. Within the OCLTT framework, we hypothesised that fish would select temperatures that maximise their AS, and thus their performance. We tested this hypothesis using intermittent flow respirometry to measure AS at, above (+2.5°C) and below (-2.5°C) the self-selected, preferred temperature (Tpref) of individual zebrafish (Danio rerio). AS was greatest 2.5°C above Tpref, which was driven by an increase in maximal metabolic rate. This mismatch between Tpref and the optimal temperature for AS suggests that factor(s) aside from AS maximisation influence the thermal preference of zebrafish.

Ocean acidification and seasonal temperature extremes combine to impair the thermal physiology of a sub-Antarctic fish

To predict the potential impacts of climate change on marine organisms, it is critical to understand how multiple stressors constrain the physiology and distribution of species. We evaluated the effects of seasonal changes in seawater temperature and near-future ocean acidification (OA) on organismal and sub-organismal traits associated with the thermal performance of Eleginops maclovinus, a sub-Antarctic notothenioid species with economic importance to sport and artisanal fisheries in southern South America. Juveniles were exposed to mean winter and summer sea surface temperatures (4 and 10 °C) at present-day and near-future pCO2 levels (~500 and 1800 μatm). After a month, the Critical Thermal maximum and minimum (CTmax, CTmin) of fish were measured using the Critical Thermal Methodology and the aerobic scope of fish was measured based on the difference between their maximal and standard rates determined from intermittent flow respirometry. Lipid peroxidation and the antioxidant capacity were also quantified to estimate the oxidative damage potentially caused to gill and liver tissue. Although CTmax and CTmin were higher in individuals acclimated to summer versus winter temperatures, the increase in CTmax was minimal in juveniles exposed to the near-future compared to present-day pCO2 levels (there was a significant interaction between temperature and pCO2 on CTmax). The reduction in the thermal tolerance range under summer temperatures and near-future OA conditions was associated with a reduction in the aerobic scope observed at the elevated pCO2 level. Moreover, an oxidative stress condition was detected in the gill and liver tissues. Thus, chronic exposure to OA and the current summer temperatures pose limits to the thermal performance of juvenile E. maclovinus at the organismal and sub-organismal levels, making this species vulnerable to projected climate-driven warming.

Inhibition of gastric acid secretion with omeprazole affects fish specific dynamic action and growth rate: Implications for the development of phenotypic stomach loss.

An acid-secreting stomach provides many selective advantages to fish and other vertebrates; however, phenotypic stomach loss has occurred independently multiple times and is linked to loss of expression of both the gastric proton pump and the protease pepsin. Reasons underpinning stomach loss remain uncertain. Understanding the importance of gastric acid-secretion to the metabolic costs of digestion and growth will provide information about the metabolic expense of acid-production and performance. In this study, omeprazole, a well characterized gastric proton pump inhibitor, was used to simulate the agastric phenotype by significantly inhibiting gastric acidification in Nile tilapia. The effects on post-prandial metabolic rate and growth were assessed using intermittent flow respirometry and growth trials, respectively. Omeprazole reduced the duration (34.4%) and magnitude (34.5%) of the specific dynamic action and specific growth rate (21.3%) suggesting a decrease in digestion and assimilation of the meal. Gastric pH was measured in control and omeprazole treated fish to confirm that gastric acid secretion was inhibited for up to 12 h post-treatment (p < 0.05). Gastric evacuation measurements confirm a more rapid emptying of the stomach in omeprazole treated fish. These findings reinforce the importance of stomach acidification in digestion and growth and present a novel way of determining costs of gastric digestion.

Personality in hatchery Atlantic salmon (Salmo salar) is associated with growth but not metabolic rate or performance

The pace of life hypothesis (POLS) predicts that personality traits, like activity and boldness, are positively correlated with growth and metabolism. Here, we assess whether personality could predict body mass, metabolic rate, and performance under stress for hatchery-raised Atlantic salmon ( Salmo salar) 15 months post fertilization. Personality was evaluated for individual fish using a series of repeated trials alongside two stressful events (PIT tagging, simulated transport), to determine performance under stress. Standard metabolic rate (SMR) was then assessed via intermittent flow respirometry, and the relationships between personality, body mass, performance, and SMR were evaluated. Fish displayed repeatable behaviours, but not in accordance with POLS hypothesis. Smaller fish were more active and responsive to stimuli, while personality was not associated with SMR. Although smaller fish and fish with higher SMR both performed better under stress, body mass was unrelated to SMR. We discuss the utility of supporting the occurrence of a wider range of growth rates and body sizes in hatchery environments, as a means of promoting greater stress tolerance as well as faster growth.

Metabolic rate and critical thermal maximum CTmax estimates for westslope cutthroat trout, Oncorhynchus clarkii lewisi.

Global warming is changing the thermal habitat of cold-water freshwater fishes, which can lead to decreased fitness and survival and cause shifts in species distributions. The Alberta population of westslope cutthroat trout (Oncorhynchus clarkii lewisi) is listed as 'Threatened' under the Canadian Species at Risk Act. The major threats to the species are the alteration in habitat and water flow, competition and hybridization with non-native trout species and climate change. Here, we conducted (i) intermittent-flow respirometry experiments with adult native westslope cutthroat trout and non-native rainbow trout (Oncorhynchus mykiss) and (ii) critical thermal maximum experiments (CTmax ) with adult westslope cutthroat trout to obtain valuable input data for species distribution models. For both species, standard metabolic rate (SMR) was lower at 10°C compared to 15°C and westslope cutthroat trout had higher SMR than rainbow trout. Although there were inter-specific differences in SMR, forced aerobic scope (using a standardized chase protocol) was different at 10°C, but no significant differences were observed at 15°C because of relative smaller differences in maximum metabolic rate between the species. CTmax of westslope cutthroat trout acclimated to 10°C was 27.0 ± 0.8°C and agitation temperature was 25.2 ± 1.0°C. The results from this study will inform and parametrize cumulative effects assessments and bioenergetics habitat modelling for the recovery planning of the species.

A novel hyperbaric swimming respirometer allows the simulation of varying swimming depths in fish respirometry studies

The understanding of swimming physiology and knowledge on the metabolic costs of swimming are important for assessing effects of environmental factors on migratory behavior.Swim tunnels are the most common experimental setups for measuring swimming performance and oxygen uptake rates in fishes; however, few can realistically simulate depth and the changes in hydrostatic pressure that many fishes experience, e.g. during diel vertical migrations. Here, we present a new hyperbaric swimming respirometer (HSR) that can simulate depths of up to 80 m. The system consists of three separate, identical swimming tunnels, each with a volume of 205 L, a control board and a storage tank with water treatment. The swimming chamber of each tunnel has a length of 1.40 m and a diameter of 20 cm. The HSR uses the principle of intermittent-flow respirometry and has here been tested with female European eels (Anguilla anguilla). Various pressure, temperature and flow velocity profiles can be programmed, and the effect on metabolic activity and oxygen consumption can be assessed. Thus, the HSR provides opportunities to study the physiology of fish during swimming in a simulated depth range that corresponds to many inland, coastal and shelf waters.

Temperature and size-dependency of lumpfish (Cyclopterus lumpus) oxygen requirement and tolerance

Lumpfish are currently produced and utilized as cleaner fish, to control sea lice infestation rates in salmon net pens, but information on environmental requirements is still limited. This study aimed to determine the zone of environmental hypoxia for two relevant fish sizes (15 and 60 g) and temperatures (5 and 12 °C), using intermittent flow respirometry (referred to as 15:5, 15:12, 60:5, 60:12), and to investigate parameters of stress in response to acute changes in dissolved oxygen (DO, % air saturation) from normoxia to 47, 63, 98 (control), 148 and 194% O2 at 10 °C. The standard and maximal metabolic rates (SMR and MMR) were measured in normoxia (n = 8), and MMR was measured at 5–6 DO levels ranging from 20−160% O2 (n = 8 per DO) to define the upper and lower boundaries of the hypoxic zone (DOlim and DOcrit). SMR, MMR and the aerobic metabolic scope (AS) increased with temperature and decreased with fish size. Similar effects of temperature and size were found on DOcrit – DOlim ranges: 20–55 (15:5), 35–147 (15:12), 21–53 (60:5) and 22–89 (60:12) % O2 air saturation. Results from acute exposure tests resulted in elevated cortisol levels at 63 and 47% O2, although not statistically significant at 47% O2. Other parameters of hypoxic or hyperoxic stress (lactate, pH, osmolality, lipid peroxidation rates, catalase activity) were not affected. Results from the present study suggest that lumpfish may experience oxygen levels in sea cages that restricts metabolism, performance and induce hypoxic stress.

Comparison of Metabolic Rates of Young of the Year Beluga (Huso huso), Sterlet (Acipenser ruthenus) and Bester Hybrid Reared in a Recirculating Aquaculture System

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

Guidelines for reporting methods to estimate metabolic rates by aquatic intermittent-flow respirometry.

ABSTRACTInterest in the measurement of metabolic rates is growing rapidly, because of the importance of metabolism in advancing our understanding of organismal physiology, behaviour, evolution and responses to environmental change. The study of metabolism in aquatic animals is undergoing an especially pronounced expansion, with more researchers utilising intermittent-flow respirometry as a research tool than ever before. Aquatic respirometry measures the rate of oxygen uptake as a proxy for metabolic rate, and the intermittent-flow technique has numerous strengths for use with aquatic animals, allowing metabolic rate to be repeatedly estimated on individual animals over several hours or days and during exposure to various conditions or stimuli. There are, however, no published guidelines for the reporting of methodological details when using this method. Here, we provide the first guidelines for reporting intermittent-flow respirometry methods, in the form of a checklist of criteria that we consider to be the minimum required for the interpretation, evaluation and replication of experiments using intermittent-flow respirometry. Furthermore, using a survey of the existing literature, we show that there has been incomplete and inconsistent reporting of methods for intermittent-flow respirometry over the past few decades. Use of the provided checklist of required criteria by researchers when publishing their work should increase consistency of the reporting of methods for studies that use intermittent-flow respirometry. With the steep increase in studies using intermittent-flow respirometry, now is the ideal time to standardise reporting of methods, so that – in the future – data can be properly assessed by other scientists and conservationists.

The energetics of social signaling during roost location in Spix's disc-winged bats.

Long-term social aggregations are maintained by multiple mechanisms, including the use of acoustic signals, which may nonetheless entail significant energetic costs. To date, however, no studies have gauged whether there are significant energetic costs to social call production in bats, which heavily rely on acoustic communication for a diversity of social tasks. We measured energetic expenditure during acoustic signaling in Spix's disc-winged bats (Thyroptera tricolor), a species that commonly uses contact calls to locate the ephemeral furled leaves that they use for roosting. To determine the cost of sound production, we measured oxygen consumption using intermittent-flow respirometry methods, with and without social signaling. Our results show that the emission of contact calls significantly increases oxygen consumption; vocal individuals spent, on average, 12.42kJ more during social signaling trials than they spent during silent trials. We also found that as resting metabolic rate increased in males, there was a decreasing probability that they would emit response calls. These results provide support to the 'allocation model', which predicts that only individuals with lower self-maintenance costs can afford to spend energy in additional activities. Our results provide a step forward in our understanding of how physiology modulates behavior, specifically how the costs of call production and resting metabolic rate may explain the differences in vocal behavior among individuals.

The effects of warming on red blood cell carbonic anhydrase activity and respiratory performance in a marine fish

Measures of fitness are valuable tools to predict species' responses to environmental changes, like increased water temperature. Aerobic scope (AS) is a measure of an individual's capacity for aerobic processes, and frequently used as a proxy for fitness. However, AS is complicated by individual variation found not only within a species, but within similar body sizes as well. Maximum metabolic rate (MMR), one of the factors determining AS, is constrained by an individual's ability to deliver and extract oxygen (O2) at the tissues. Recently, data has shown that red blood cell carbonic anhydrase (RBC CA) is rate-limiting for O2 delivery in red drum (Sciaenops ocellatus). We hypothesized increased temperature impacts MMR and RBC CA activity in a similar manner, and that an individual's RBC CA activity drives individual variation in AS. Red drum were acutely exposed to increased temperature (+6 °C; 22 °C to 28 °C) for 24 h prior to exhaustive exercise and intermittent-flow respirometry at 28 °C. RBC CA activity was measured before temperature exposure and after aerobic performance. Due to enzymatic thermal sensitivity, acute warming increased individual RBC CA activity by 36%, while there was no significant change in the control (22 °C) treatment. Interestingly, average MMR of the acute warming treatment was 36% greater than that of control drum. However, we found no relationships between individual RBC CA activity and their respective MMR and AS at either temperature. While warming similarly affects RBC CA activity and MMR, RBC CA activity is not a predictor of individual MMR.

An investigation of links between metabolic rate and feed efficiency in European sea bass Dicentrarchus labrax.

Feed efficiency (FE) is the amount of body weight gain for a given feed intake. Improving FE through selective breeding is key for sustainable finfish aquaculture but its evaluation at individual level is technically challenging. We therefore investigated whether individual routine metabolic rate (RMR) was a predictor of individual FE in the European sea bass Dicentrarchus labrax, a major species in European mariculture. The European sea bass has three genetically distinct populations across its geographical range, namely Atlantic (AT), West Mediterranean (WM), and East Mediterranean (EM). We compared FE and RMR of fish from these three populations at 18 or 24 °C. We held 200 fish (62 AT, 66 WM, and 72 EM) in individual aquaria and fed them from ad libitum down to fasting. FI was assessed for an ad libitum feeding rate and for a fixed restricted ration (1% of metabolic body weight·day-1, with metabolic body weight = body weight0.8). After being refed 12 wk in a common tank, individual RMR was measured over 36 h by intermittent flow respirometry. There was a significant effect of temperature whereby fish at 18 °C had greater mean FE (P < 0.05) and lower RMR (P < 0.001). There was also a significant effect of population, where AT fish had lower FE (P < 0.05) and greater RMR (P < 0.001) than WM and EM, at both temperatures. Despite these differences in temperature and population means, individual FE and RMR were not significantly correlated (P > 0.05). Therefore, although the results provide evidence of an association between metabolic rate and FE, RMR was not a predictor of individual FE, for reasons that require further investigation.