Morphology and metabolic traits related to swimming performance in Australasian snapper (Chrysophrys auratus) selected for fast growth.

Changes in body shape are linked to swimming performance and become relevant for selective breeding programmes in cultured finfish. We studied how the selection for fast growth could affect phenotypes by investigating the relationship between swimming performance and body shape. We also investigated how swimming might affect plasma metabolite concentrations. Critical swimming speed (UCrit), body traits (e.g., BW, body weight; BL, body length; K, condition factor), and plasma lactate and glucose concentrations were evaluated in two cohorts of Australasian snapper (Chrysophrys auratus): one derived from wild broodstock (F1), and the other selected for fast growth (F4). UCrit tests (n = 8) were applied in groups of 10 snapper of similar BW (71.7 g) and BL (14.6 cm). The absolute or relative UCrit values of both cohorts were similar (0.702 m⋅s-1 and 4.795 BL⋅s-1, respectively), despite the F4 cohort displaying a higher K. A positive correlation between K and absolute UCrit (Pearson's r = 0.414) was detected in the F4 cohort, but not in the F1 cohort, which may be linked to differences in body shape. A negative correlation between relative UCrit and body size (Pearson's r between -0.682 and -0.501), but no correlation between absolute UCrit and body size, was displayed in both cohorts. Plasma lactate and glucose concentrations were higher in the F4 cohort at UCrit. Whether a longer selective breeding programme could result in more changes in body shape, potentially affecting swimming performance, should be explored, along with the potential outcomes of the differences in metabolic traits detected.

Swimming Performance in Large Yellow Croaker: Effects of Group Size, Test Protocol, and Recovery Time On Critical Swimming Speed.

Swimming is critical for fish survival, and little attention has been paid to the swimming performance of large yellow croaker, the largest farmed marine fish in China. To address this gap, we conducted a study to measure the critical swimming speed (Ucrit) of 1050 croaker in a designed swim test flume. Our findings shed light on the effects of group size, Ucrit test protocol, and recovery time on swimming performance. The water flow in the swim flume increased steadily and linearly. The linear fit equation was y = 2.89x + 1.79 with an R2 of 0.99. With the help of the swim flume, we found that group size, and the Ucrit test protocol had a significant effect on the Ucrit values, except for the recovery time: The Ucrit values obtained in the ramp-Ucrit test averaged 28.32 ± 6.11 cm.s-1, which was significantly lower than that obtained in the traditional Ucrit test of 32.75 ± 7.60 cm.s-1; The Ucrit value of a group size of 50 fish was 33.51 ± 5.96 cm.s-1, which was significantly higher than that of a group of 200 fish (28.49 ± 6.37 cm.s-1). These results provide insights into the swimming performance of large yellow croaker and can be used to standardize the swimming test protocols.

Method dependency of maximum oxygen uptake rate and its repeatability in the Gulf killifish, Fundulus grandis.

The maximum rate at which fish can take up oxygen from their environment to fuel aerobic metabolism is an important feature of their physiology and ecology. Methods to quantify maximum oxygen uptake rate (MO2), therefore, should reliably and reproducibly estimate the highest possible MO2 by an individual or species under a given set of conditions (peak MO2). This study determined peak MO2 and its repeatability in Gulf killifish, Fundulus grandis, subjected to three methods to elevate metabolism: swimming at increasing water speeds, during recovery after an exhaustive chase, and after ingestion of a large meal. Estimates of peak MO2 during swimming and after an exhaustive chase were repeatable across two trials, whereas peak MO2 after feeding was not. Peak MO2 determined by the three methods was significantly different from one another, being highest during swimming, lowest after an exhaustive chase, and intermediate after feeding. In addition, peak MO2 during recovery from an exhaustive chase depended on the length of time of recovery: in nearly 60% of the trials, values within the first hour of the chase were lower than those measured later. A novel and important finding was that an individual's peak MO2 was not repeatable when compared across methods. Therefore, the peak MO2 estimated for a group of fish, as well as the ranking of individual MO2 within that group, depends on the method used to elevate aerobic metabolism.

Interaction of total dissolved gas supersaturation and suspended sediment on swimming performance of bighead carp (Hypopthalmichthys nobilis).

When dams discharge floodwaters, the river downstream often becomes supersaturated in total dissolved gases (TDG) and contains high volumes of suspended sediments (SS). Supersaturated TDG and high SS concentrations in water may affect fish physiologically in ways that manifest in swimming performance. Despite increasing awareness of the separate effects of TDG supersaturation and SS, knowledge about their synergistic effects remains unknown. To explore the interactive effects of TDG and SS on the swimming performance of bighead carp, the juveniles were exposed to 100, 110, 115, 120, 125, 130, 135, and 140% of TDG-supersaturated water with SS concentrations of 0, 50, 100, and 150 mg/L, respectively, and the critical swimming ability speed (Ucrit ) and burst swimming ability speed (Uburst ) were measured. The results indicated that the swimming ability (Ucrit and Uburst ) decreased when TDG levels and SS concentrations increased. TDG and SS did not interact significantly to decrease both Ucrit and Uburst . In contrast, exposure to TDG alone significantly decreased both Ucrit and Uburst , whereas exposure to SS alone decreased only Uburst . In addition, our results suggested that there was a negative linear relationship between TDG and fatigue time. Swimming ability can decline significantly due to high TDG levels (>130%). Therefore, high TDG levels (>130%) should be restricted during reservoir operation to prevent the stress caused by TDG.

Swimming ability of cyprinid species (subfamily schizothoracinae) at high altitude.

The primary objective of this investigation was to study the effect of altitude on fish swimming ability. Different species were tested to ensure that the differences observed are not associated with a single species. Fish critical swimming speed and burst speed were determined using stepped-velocity tests in a Brett-type swimming respirometer. Based on the effects of water temperature and dissolved oxygen, it is clear that the swimming ability of fish decreases as altitude increases. Further, because the effects of high altitude on fish physiology go beyond the effects of lower temperature and dissolved oxygen, we recommend that fish swimming ability be tested at an altitude similar to the target fishway site to ensure the validity of fish data used for fishway design.

Swimming performance of Cyprinus carpio (Carp) in China.

Cyprinus carpio (Carp) is a fish of great economic importance in China. However, its population has declined considerably due to the construction of barrages. Thus, fishways need to be constructed at barrages to protect fish resources. It is essential for the fishway design to study the swimming performance of carp. By applying incremental flow velocities in a glass open-type flume, three indicators of swimming performance of the carp in China with the body length (BL) of 13-21 cm, including the induced flow velocity (IFV), the critical swimming speed (Ucrit) and the burst swimming speed (Uburst), are systematically assessed. The correlation between the swimming performance and the BL is also analyzed. The results indicate that the IFV of the carp is 15.56 ± 1.79 cm/s, which is not significantly influenced by the BL. The value of Ucrit varies from 60 to 82 cm/s and gradually increases with the increasing value of BL. The relative critical swimming speed (U'crit) is 4.23 ± 0.28 BL/s and gradually decreases with the increasing value of BL. The value of Uburst ranges from 77.2 to 105.1 cm/s, which is linearly positively correlated to BL. The relative burst swimming speed (U'burst) is 5.42 ± 0.39 BL/s. The value of Uburst is approximately 1.28 times of that of Ucrit for the carps with the same BL. These findings are meaningful to the further study of ecological behavior and to the fishway design and optimization of carps.

Juvenile semi-wild fish have a higher metabolic rate than farmed fish.

Fish from commercially farmed stocks are often released into the natural environment to supplement wild populations. This practice is often applied to salmonid fish as they are an essential fishery resource and also used for recreational angling. However, farmed fish tend to show lower survival rates after release than wild fish. For this reason, the release of semi-wild fish is increasingly used in Japan; these fish are generated using female fish from domesticated stocks and male fish of wild origin. The survival rate of released semi-wild fish is higher than that of farmed fish, but the reason for this is unknown. This study compared the metabolism and swimming performance of semi-wild and farmed masu salmon (Oncorynchus masou). The analyses showed that resting metabolic rate (RMR), maximum metabolic rate (MMR) and swimming speeds that minimize energy costs of travel (optimal swimming speed) were higher in semi-wild fish than in farmed fish. Critical swimming speed did not differ significantly between the two groups of fish. Semi-wild fish with high RMR may have a social status advantage over farmed fish because a previous study reported that SMR, which is the value closest to basal metabolism significantly affects feeding motivation. This means that individuals with higher social status may be more motivated to feed. As RMR is proportional to food requirements, then release programs should be planned taking food resources at the release site into consideration.

Sublethal exposure to Microcystis aeruginosa extracts during the yolk-sac larval stage reduces aerobic swimming speed in juvenile zebrafish.

This study examined whether the aerobic swimming capacity of zebrafish juveniles is affected by the exposure of the yolk-sac larvae to sublethal concentration of Microcystis aeruginosa extract (200 mg dw L-1). Critical swimming speed significantly decreased in the pre-exposed fish (9.2 ± 1.0 vs 11.3 ± 1.4 TL s-1 in the control group). Exposure did not have any significant effects on the shape of the heart ventricle, rate of skeletal abnormalities, and growth or survival rates. Decreased swimming performance due to the early and short exposure to M. aeruginosa could have negative impacts on fish in the wild.

Swimming energetics of Atlantic salmon in relation to extended fasting at different temperatures.

Predicted future warming of aquatic environments could make fish vulnerable to naturally occurring fasting periods during migration between feeding and spawning sites, as these endeavours become energetically more expensive. In this study, Atlantic salmon (Salmo salar) acclimated to midrange (9°C) or elevated suboptimal (18°C) temperatures were subjected to critical (Ucrit) and sustained (4 hours at 80% Ucrit) swimming trials before and after 4 weeks of fasting. Fasting caused weight losses of 7.3% and 8.3% at 9°C and 18°C, respectively. The Ucrit was unaffected by fasting, but higher at 18°C. Fatigue was associated with higher plasma cortisol, osmolality, Na+ and Cl- at 18°C, and ionic disturbances were higher in fasted fish. All fish completed the sustained swim trials while maintaining constant oxygen uptake rates (MO2), indicating strictly aerobic swimming efforts. At low swimming speeds MO2 was downregulated in fasted fish by 23.8% and 15.6% at 9°C and 18°C, respectively, likely as an adaptation to preserve resources. However, at higher speeds MO2 became similar to fed fish showing that maximum metabolic rates were maintained. The changes in MO2 lowered costs of transport and optimal swimming speeds in fasted fish at both temperatures, but these energetic alterations were smaller at 18°C while routine MO2 was 57% higher than at 9°C. As such, this study shows that Atlantic salmon maintain both glycolytic and aerobic swimming capacities after extended fasting, even at elevated suboptimal temperatures, and adaptive metabolic downregulation provides increased swimming efficiency in fasted fish. Although, improved swimming energetics were smaller when fasting at the higher temperature while metabolism becomes elevated. This could affect migration success in warming climates, especially when considering interactions with other costly activities such as coping with parasites obtained when passing aquaculture sites during seaward travel or gonad development while being voluntarily anorexic during upriver travel to spawning grounds.

Ontogeny of swimming performance of hatchery-reared post-larvae and juvenile fish: a case of two threatened Mediterranean species.

Swimming performance is a well-established key physiological parameter of fish that is highly linked to their fitness in the wild. In the context of fish restocking purposes, it therefore appears crucial to study this specific behaviour. Here, the authors investigated intra and interspecies differences in the swimming performance of hatchery-reared post-larvae and juveniles belonging to two Mediterranean candidate threatened species, the common dentex, Dentex dentex (Sparidae), and the brown meagre, Sciaena umbra (Sciaenidae), with body sizes ranging from 8 to 37 mm total length (TL, from 24 to 58 days post-hatch). The swimming abilities were estimated through the calculation of their critical swimming speed (Ucrit ), their relative Ucrit and their Reynolds number (Re ). Two different patterns were observed between D. dentex and S. umbra, showing a different effect of ontogeny on the performance of both species. The relative Ucrit of S. umbra decreased linearly through ontogeny, whereas the relative Ucrit and Ucrit of D. dentex increased linearly through the range of sizes tested. The ontogenetic change in Ucrit of S. umbra occurred in two stages: a first stage of sharp improvement and a second stage of a slow decrease in performance. Both stages were separated by a breakpoint that coincided with the appearance of a refusal to swim behaviour that occurred shortly after the end of metamorphosis and can potentially be associated with the establishment of this species sedentary behaviour. The swimming performance of both species showed ontogenetic differences. Sciaena umbra had the highest relative performance when its body sizes were the smallest, whereas D. dentex showed the highest relative performance when its body sizes were the largest. These results will be linked to future research on both of these species concerning their escape, exploratory and predatory behaviours, and for restocking purposes to draw a more realistic overview of hatchery-reared juvenile performance. Knowledge of both species' behavioural and swimming performance through ontogeny is important to consider when using hatchery-reared fish juveniles for restocking, as size-at-release can have a large impact on fish survival and thus on restocking success.

Impacts of diethylhexyl phthalate and overfeeding on physical fitness and lipid mobilization in Danio rerio (zebrafish).

As the prevalence of obesity has steadily increased on a global scale, research has shifted to explore potential contributors to this pandemic beyond overeating and lack of exercise. Environmental chemical contaminants, known as obesogens, alter metabolic processes and exacerbate the obese phenotype. Diethylhexyl phthalate (DEHP) is a common chemical plasticizer found in medical supplies, food packaging, and polyvinyl materials, and has been identified as a probable obesogen. This study investigated the hypothesis that co-exposure to DEHP and overfeeding would result in decreased lipid mobilization and physical fitness in Danio rerio (zebrafish). Four treatment groups were randomly assigned: Regular Fed (control, 10 mg/fish/day with 0 mg/kg DEHP), Overfed (20 mg/fish/day with 0 mg/kg DEHP), Regular Fed + DEHP (10 mg/fish/day with 3 mg/kg DEHP), Overfed + DEHP (20 mg/fish/day with 3 mg/kg DEHP). After 24 weeks, swim tunnel assays were conducted on half of the zebrafish from each treatment to measure critical swimming speeds (Ucrit); the other fish were euthanized without swimming. Body mass index (BMI) was measured, and tissues were collected for blood lipid characterization and gene expression analyses. Co-exposure to DEHP and overfeeding decreased swim performance as measured by Ucrit. While no differences in blood lipids were observed with DEHP exposure, differential expression of genes related to lipid metabolism and utilization in the gastrointestinal and liver tissue suggests alterations in metabolism and lipid packaging, which may impact utilization and ability to mobilize lipid reserves during physical activity following chronic exposures.

Sublethal exposure to Microcystis aeruginosa extracts during embryonic development reduces aerobic swimming capacity in juvenile zebrafish.

In the last decades, cyanobacterial harmful algal blooms (CyanoHABs) pose an intensifying ecological threat. Microcystis aeruginosa is a common CyanoHAB species in freshwater ecosystems, with severe toxic effects in a wide range of organisms. In the present paper we examined whether transient and short (48 h) exposure of fish embryos to sublethal levels of M. aeruginosa crude extract (200 mg biomass dw L-1) affects swimming performance at later life stages (end of metamorphosis, ca 12 mm TL, 22,23 days post-fertilization). Pre-exposed metamorphosing larvae presented a significant decrease in swimming performance (9.7 ± 1.6 vs 11.4 ± 1.7 TL s-1 in the control group, p < 0.01), and a significant decrease in the ventricle length-to-depth ratio (1.23 ± 0.15 vs 1.42 ± 0.15 in control fish, p < 0.05). In addition, extract-exposed fish presented significantly elevated rates of vertebral abnormalities (82 ± 13% vs 7 ± 4% in the control group), mainly consisting of the presence of extra neural and haemal processes. No significant differences between groups were detected in survival and growth rates. Results are discussed in respect to the mechanisms that might mediate the detected cyanobacterial effects. This is the first evidence of a direct link between sublethal exposure to M. aeruginosa during the embryonic period and swimming performance at later life-stages. Decreased swimming performance, altered cardiac shape, and elevated vertebral abnormalities in response to early exposure to M. aeruginosa could have significant effects on fish populations in the wild.

Intracellular taurine deficiency impairs cardiac contractility in rainbow trout (Oncorhynchus mykiss) without affecting aerobic performance.

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

Swimming behaviour of silver carp (Hypophthalmichthys molitrix) in response to turbulent flow induced by a D-cylinder.

Turbulence is a complex hydraulic phenomenon which commonly occurs in natural streams and fishways. Riverine fish are subjected to heterogeneous flow velocities and turbulence, which may affect their movements and ability to pass the fishways. However, studies focusing on fish response to turbulent flows are lacking for many species. Here we investigate the effects of the turbulence created by a vertical half-cylinder of various diameters (1.9, 2.5, 3.2 and 5.0 cm) on the swimming ability and behaviour of silver carp, Hypophthalmichthys molitrix. The large D-cylinders (3.0 and 5.0 cm) create specific vorticity and reduced velocities areas in their vicinity, which favours flow refuging behaviours (FRBs) and thus increased relative critical swimming speeds (Urcrit , BL/s) of silver carp, by comparison to free-flow conditions and cylinders of smaller diameter (1.9 and 2.5 cm). The flow speed at which silver carp maximized FRBs such as Karman gaiting downstream of the cylinder, holding position in the bow wake or entraining on the side ranged from 40 to 70 cm s-1 , depending on fish body size. When holding station near a cylinder under optimal flow speeds, the distance between the fish and the cylinder is related to the size of the fish, but also to the size of the cylinder and the produced vortices. The optimal holding region in the drag wake of the cylinder ranged from 28 to 40 cm downstream of the centre of the cylinder, depending on the size of the fish. Smaller fish, however, tend to use the reduced velocities areas located in the bow wake of the large cylinders. We hypothesize that fish will display FRBs, including maintaining a Karman gait in turbulent flow, when the ratio of the cylinder diameter to their body length is between 1:3 and 1:4. They also match their tail beat frequency to the vortex shedding frequency of the cylinder. Our results provide a better understanding of how silver carp respond to turbulent flows around physical structures, with implications for the design of nature-like fishways or exclusion devices in both its native and invasive ranges.

Use of complex physiological traits as ecotoxicological biomarkers in tropical freshwater fishes.

We review the use of complex physiological traits, of tolerance and performance, as biomarkers of the toxicological effects of contaminants in subtropical and tropical freshwater fishes. Such traits are growing in relevance due to climate change, as exposure to contaminants may influence the capacity of fishes to tolerate and perform in an increasingly stressful environment. We review the evidence that the critical oxygen level, a measure of hypoxia tolerance, provides a valuable biomarker of impacts of diverse classes of contaminants. When coupled with measures of cardiorespiratory variables, it can provide insight into mechanisms of toxicity. The critical thermal maximum, a simple measure of tolerance of acute warming, also provides a valuable biomarker despite a lack of understanding of its mechanistic basis. Its relative ease of application renders it useful in the rapid evaluation of multiple species, and in understanding how the severity of contaminant impacts depends upon prevailing environmental temperature. The critical swimming speed is a measure of exercise performance that is widely used as a biomarker in temperate species but very few studies have been performed on subtropical or tropical fishes. Overall, the review serves to highlight a critical lack of knowledge for subtropical and tropical freshwater fishes. There is a real need to expand the knowledge base and to use physiological biomarkers in support of decision making to manage tropical freshwater fish populations and their habitats, which sustain rich biodiversity but are under relentless anthropogenic pressure.

A Swimming-based Assay to Determine the Exercise Capacity of Adult Zebrafish Cardiomyopathy Models.

Exercise capacity, measured by treadmill in humans and other mammals, is an important diagnostic and prognostic index for patients with cardiomyopathy and heart failure. The adult zebrafish is increasingly used as a vertebrate model to study human cardiomyopathy due to its conserved cardiovascular physiology, convenience for genetic manipulation, and amenability to high-throughput genetic and compound screening. Owing to the small size of its body and heart, new phenotyping assays are needed to unveil phenotypic traits of cardiomyopathy in adult zebrafish. Here, we describe a swimming-based functional assay that measures exercise capacity in an adult zebrafish doxorubicin-induced cardiomyopathy model. This protocol can be applied to any adult zebrafish model of acquired or inherited cardiomyopathy and potentially to other cardiovascular diseases. Graphic abstract: Clinical relevance of the swimming-based phenotyping assay in adult zebrafish cardiomyopathy models.

Impact of TDG supersaturation on native fish species under different hydropower flood discharge programs.

Total dissolved gas (TDG) supersaturation caused by the operation of hydropower stations can threaten the survival and swimming performance of fish species. Different modes of hydropower flood discharges (regular vs. intermittent) from the Dagangshan hydropower station in China were studied in July and September 2017 to study the impact of TDG supersaturation on two native fish species in the downstream Dadu River. The average TDG supersaturation value was 114.3% in July under the regular discharge mode. In September, the supersaturation of TDG fluctuated in response to the intermittent discharge mode with an average TDG of 119.3%. Apparent gas bubble trauma was found on young-of-the-year (YOY) Prenant's schizothoracin and elongate loach in cages at different water depths during the flood discharge period. The mortality rate of YOY Prenant's schizothoracin and elongate loach in cages with water depths of 0-1 m were 16.25% and 2.5%, respectively, in July. The fluctuating TDG levels with higher peaks in September caused higher fish mortality rates. The final mortality rates of YOY Prenant's schizothoracin and elongate loach in cages with water depths of 0-1 m were 75% and 33.75%, respectively. Fish in the cages at a 0-3 m water depth survived better than those in the cages at a 0-1 m water depth. The critical swimming speeds (Ucrit) of YOY Prenant's schizothoracin and elongate loach without exposure to TDG supersaturation were 11.64 and 16.76 BL s-1, respectively. Ucrit decreased significantly after experiencing the flood discharge period and recovered to the normal level after experiencing the corresponding interval period.

The effect of fasting period on swimming performance, blood parameters and stress recovery in Atlantic salmon post smolts.

In this study, Atlantic salmon post smolts (~250 g, ~29 cm) were fasted for four weeks at 12 °C in full strength seawater. During this period, the critical swimming speed (Ucrit) was measured after 1, 2 and 4 weeks of fasting, as well as in a fed control group. Furthermore, blood samples were taken in each treatment group prior to the swim test, at fatigue, and following 3 h and 24 h of subsequent recovery. Four weeks of fasting gradually reduced the condition factor from 1.03 to 0.89. However, the Ucrit remained statistically unaffected at 3.5 body lengths s-1. Exhaustive exercise stress caused large increases in plasma osmolality, [Cl-], [Na+], [Ca2+], [lactate] and [cortisol], while haematocrit and [haemoglobin] also increased. Plasma ions and lactate had increased further after 3 h recovery, and osmolality, [Cl-] and [Na+] were still elevated above control levels after 24 h while other blood parameters were fully recovered. Osmotic disturbances may therefore be considered the most challenging stressor during strenuous exercise in seawater. Only minor effects of fasting period on blood parameters in response to exhaustive exercise were detected, which included slightly higher osmotic disturbances and a repressed response in red blood cell recruitment at fatigue in fasted fish. Furthermore, the 4-week fasting group had a reduced cortisol response following fatigue compared to the other treatment groups. In conclusion, these results show that Atlantic salmon maintain their full swimming capacity as well as their ability to respond and recover from acute stress during an extended period of food deprivation.

Thermal variation near the thermal optimum does not affect the growth, metabolism or swimming performance in wild Atlantic salmon Salmo salar.

Typically, laboratory studies on the physiological effects of temperature are conducted using stable acclimation temperatures. Nonetheless, information extrapolated from these studies may not accurately represent wild populations living in thermally variable environments. The aim of this study was to compare the growth rate, metabolism and swimming performance of wild Atlantic salmon exposed to cycling temperatures, 16-21°C, and stable acclimation temperatures, 16, 18.5, 21°C. Growth rate, metabolic rate, swimming performance and anaerobic metabolites did not change among acclimation groups, suggesting that within Atlantic salmon's thermal optimum range, temperature variation has no effect on these physiological properties.

An acute increase in water temperature can decrease the swimming performance and energy utilization efficiency in rainbow trout (Oncorhynchus mykiss).

In order to evaluate the effects of acute temperature exposure on the swimming performance of rainbow trout (Oncorhynchus mykiss), the critical swimming speed (Ucrit) and oxygen consumption rates (MO2) were determined at different temperatures (13.2, 18.4, and 22.5 °C). The Ucrit and MO2 of different body mass (109.44, 175.74, and 249.42 g) fish were also obtained at 13.4 °C. The Ucrit first increased as the temperature increased from 13.2 to 15.2 °C, which was calculated to be the optimal temperature for the Ucrit, and then decreased with increasing temperature. The optimal swimming speed (Uopt) showed a similar trend to the Ucrit. At a given swimming speed, the MO2 and cost of transport (COT) were significantly higher at 22.5 than at 13.2 °C, suggesting the energy utilization efficiency decreased with increasing temperature. The absolute values of Ucrit and Uopt increased as the body mass increased from 109.44 to 249.42 g, whereas the relative values decreased. Although not statistically significant, the maximum metabolic rate (MMR) tended to increase with temperature but decrease with body mass. Results can be of value in understanding the behavioral and physiological response of rainbow trout to acute temperature change.