The effect of prolonged exercise training on swimming performance and the underlying biochemical mechanisms in juvenile common carp (Cyprinus carpio)

The effect of swimming activity and feed restriction of rainbow trout (Oncorhynchus mykiss) on water quality and fish-plant growth performance in aquaponics

In this study, we investigated the effects of swimming activity and feed restriction on juvenile rainbow trout (Oncorhynchus mykiss) in decoupled aquaponic systems. Our focus was on assessing their impact on water quality parameters within the aquaponic setup and evaluating the growth performance of the fish, including final weight (FW), condition factor (K), coefficient of variation (c.v.) in weight, specific growth rate (SGR), total feed intake (g/fish), feed conversion rate (FCR), hepatosomatic index (HSI), and viscerosomatic index (VSI), as well as the growth of lettuce (Lactuca sativa L. var. elmaria). The study involved 108 juvenile rainbow trout with an average initial weight of 26.54 ± 0.36 g and 60 ten-day-old lettuce seedlings, over a period of 42 days. We designed four treatment groups, each with three fish tanks: static ad libitum (SA), where fish were in static water conditions and fed to satiation; static restriction (SR), with fish in static water and a 25% feed restriction; current ad libitum (CA), where fish experienced forced swimming at 1 BL s-1; and current restriction (CR), with swimming exercise at 1 BL s-1 and a 25% feed restriction. Using a flow rate of 1 BL s-1 in the tanks for rainbow trout yielded several benefits. Notably, the fish in the CA group exhibited increased feed intake (60 ± 1.78 g fish-1) and enhanced fish growth with an FW of 91.72 ± 0.91 g, compared to the SA group (55.88 ± 0.88 g fish-1 for feed intake and 89.26 ± 0.81 g for FW). In contrast, the CR group showed a reduced feed intake (39.02 ± 2.78 g fish-1) and a lower FW (67.85 ± 1.49 g) compared to the CA group. In addition, the CA group demonstrated positive contributions to fish development with a reduced HSI (1.26 ± 0.02) in comparison to the SA group (1.56 ± 0.14). Inadequate nutrient provisioning in the SR and CR groups negatively impacted fish growth and system efficiency. Our findings suggest that optimizing water flow and feed benefits fish and plants and enhances system sustainability.

Building adjustment capacity to cope with running water in cultured grass carp through flow stimulation conditions

The adaptability of cultured fish to complex flow conditions is crucial for their survival after being released into the wild. Running water in natural environments poses significant challenges for the proliferation and release of cultured fish. This study aimed to investigate the effects of flow stimulation on the adjustment capacity of cultured fish to cope with running water. The target fish were cultured grass carp. An annular flume was used to conduct tests on training and control groups. The results demonstrated an enhancement in the adjustment capacity of cultured fish following appropriate flow stimulation training. (1) The trained fish exhibited a heightened preference for low-velocity areas. (2) The trained fish displayed the ability to select a route characterized by low energy consumption, predominantly following the periphery of the low-velocity area. This suggested that an appropriate flow velocity could improve the sensitivity of training fish to water flow information, and their adjustment capacity to cope with running water improved to a certain extent. A higher adjustment capacity allowed them to process flow rate information rapidly and identify a migration strategy with lower energy consumption. This study provides a useful reference for enhancing the survival rate of grass carp through stock enhancement initiatives and contributes to the sustainability of freshwater ecosystems.

Continuous flow stimulation had no significant effect on the growth rate but was conducive to the swimming performance, spontaneous behavior, and nonspecific immune parameter of juvenile Percocypris pingi

Flow stimulation before release into the wild may contribute to improved survivability of farmed fish. However, the effects of flow stimulation on the survival rate of fish depend on the fish species and exercise regime, such as exercise type, duration, and intensity. In this study, juvenile Percocypris pingi swam for 18 h per day for 8 weeks under different water speeds, 3 cm s-1 (control) and 1, 2, and 4 body lengths (bl) s-1 , at 20°C. Then, parameters related to the growth rate, swimming capacity, spontaneous activity, and immune function were measured. We found that (1) continuous flow stimulation had no significant influence on the growth but was conducive to the increase in the relative carcass mass; (2) continuous flow stimulation at 2 or 4 bl s-1 enhanced the aerobic swimming capacity (Ucrit ), which may be due to an increase in anaerobic exercise capacity (endurance time) rather than to changes in maximum metabolic rate and aerobic scope; (3) continuous flow stimulation at 4 bl s-1 led to a significant increase in spontaneous activity, which was mainly due to the higher percent time spent moving as compared with the controls; and (4) continuous flow stimulation at 2 bl s-1 may contribute to improving the nonspecific immune parameter (lysozyme activity) in juvenile P. pingi. Our findings suggest that continuous flow stimulation at 2 or 4 bl s-1 for 18 h per day for 56 days at 20°C before release in wild may be a suitable training regime for improving the survival rate of cultured juvenile P. pingi.

Exercise training does not affect heat tolerance in Chinook salmon (Oncorhynchus tshawytscha)

The progression of climate warming will expose ectotherms to transient heatwave events and temperatures above their tolerance range at increased frequencies. It is therefore pivotal that we understand species' physiological limits and the capacity for various controls to plastically alter these thresholds. Exercise training could have beneficial impacts on organismal heat tolerance through improvements in cardio-respiratory capacity, but this remains unexplored. Using juvenile Chinook salmon (Oncorhynchus tshawytscha), we tested the hypothesis that exercise training improves heat tolerance through enhancements in oxygen-carrying capacity. Fish were trained once daily at 60% of their maximum sustainable swim speed, U_CRIT, for 60 min. Tolerance to acute warming was assessed following three weeks of exercise training, measured as the critical thermal maximum (CT_MAX). CT_MAX measurements were coupled with examinations of the oxygen carrying capacity (haematocrit, haemoglobin concentration, relative ventricle size, and relative splenic mass) as critical components of the oxygen transport cascade in fish. Contrary to our hypothesis, we found that exercise training did not raise the CT_MAX of juvenile Chinook salmon with a mean CT_MAX increase of just 0.35 °C compared to unexercised control fish. Training also failed to improve the oxygen carrying capacity of fish. Exercise training remains a novel strategy against acute warming that requires substantial fine-tuning before it can be applied to the management of commercial and wild fishes.

Variations in cost of transport and their ecological consequences: a review

Movement is essential in the ecology of most animals, and it typically consumes a large proportion of individual energy budgets. Environmental conditions modulate the energetic cost of movement (cost of transport, COT), and there are pronounced differences in COT between individuals within species and across species. Differences in morphology affect COT, but the physiological mechanisms underlying variation in COT remain unresolved. Candidates include mitochondrial efficiency and the efficiency of muscle contraction-relaxation dynamics. Animals can offset increased COT behaviourally by adjusting movement rate and habitat selection. Here, we review the theory underlying COT and the impact of environmental changes on COT. Increasing temperatures, in particular, increase COT and its variability between individuals. Thermal acclimation and exercise can affect COT, but this is not consistent across taxa. Anthropogenic pollutants can increase COT, although few chemical pollutants have been investigated. Ecologically, COT may modify the allocation of energy to different fitness-related functions, and thereby influence fitness of individuals, and the dynamics of animal groups and communities. Future research should consider the effects of multiple stressors on COT, including a broader range of pollutants, the underlying mechanisms of COT and experimental quantifications of potential COT-induced allocation trade-offs.

Effects of Aerobic Exercise Training on the Growth, Swimming Performance, Antipredation Ability and Immune Parameters of Juvenile Rock Carp (Procypris rabaudi)

Many studies have found that aerobic exercise training at a moderate water velocity can improve the growth, swimming performance and survival rate of fish. To investigate the effects of aerobic exercise training on the growth, swimming performance, antipredation ability and immune parameters of rock carp, juveniles were placed in training channels with different water velocities (i.e., 3 cm s−1, 1 (body length s−1) bl s−1, 2 bl s−1 and 4 bl s−1) for 6 weeks. Then, the specific growth rate, critical swimming speed (Ucrit) and its metabolism, constant acceleration speed (Ucat), survival rate under predation, spleen index, lysozyme (LZM) activity and immunoglobulin (IgM) level were measured. Training showed no significant effect on the length-specific growth rate, weight-specific growth rate, Ucrit, maximum metabolic rate (MMR), metabolic scope (MS), Ucat or spleen index. The resting metabolic rates (RMRs) of the 2 bl s−1 and 4 bl s−1 training groups were significantly higher than those of the control group and 1 bl s−1 training group. The survival rate of the 1 bl s−1 training group in the presence of predators was significantly higher than that of the control group but significantly lower than those of the 2 bl s−1 and 4 bl s−1 training groups. The LZM activity of the 4 bl s−1 training group was significantly higher than that of the control group. The IgM level of the 2 bl s−1 training group was significantly higher than that of the control group. These data indicate that aerobic exercise training does not improve the growth and swimming performance of juvenile rock carp but can improve their antipredation ability and immunologic function.

Better together: Cross-tolerance induced by warm acclimation and nitrate exposure improved the aerobic capacity and stress tolerance of common carp Cyprinus carpio

Climate warming is a threat of imminent concern that may exacerbate the impact of nitrate pollution on fish fitness. These stressors can individually affect the aerobic capacity and stress tolerance of fish. In combination, they may interact in unexpected ways where exposure to one stressor may heighten or reduce the resilience to another stressor and their interactive effects may not be uniform across species. Here, we examined how nitrate pollution under a warming scenario affects the aerobic scope (AS), and the hypoxia and heat stress susceptibility of a generally tolerant fish species, common carp Cyprinus carpio. We used a 3 × 2 factorial design, where fish were exposed to one of three ecologically relevant levels of nitrate (0, 50, or 200 mg NO₃^- L^-1) and one of two temperatures (18 °C or 26 °C) for 5 weeks. Warm acclimation increased the AS by 11% due to the maintained standard metabolic rate and increased maximum metabolic rate at higher temperature, and the AS improvement seemed greater at higher nitrate concentration. Warm-acclimated fish exposed to 200 mg NO₃^- L^-1 were less susceptible to acute hypoxia, and fish acclimated at higher temperature exhibited improved heat tolerance (critical thermal maxima, CTMax) by 5 °C. This cross-tolerance can be attributed to the hematological results including maintained haemoglobin and increased haematocrit levels that may have compensated for the initial surge in methaemoglobin at higher nitrate exposure.

Qingbo, a common cyprinid fish, responds diversely in behavior and locomotion to predators with different hunting modes

Almost all prey live in habitats with predators with different hunting modes; however, most studies on predation have investigated the effects of only one predator at a time. In this study, we aimed to investigate whether qingbo (Spinibarbus sinensis), a common cyprinid fish, responds differently to active hunting and ambush predators and how qingbo responds when both types of predators coexist. Juvenile qingbo were subjected to catfish (Clarias fuscus, active hunter) exposure, snakehead fish (Channa argus, ambush hunter) exposure, or mixed predator exposure (catfish and snakehead coexistence) for a duration of 60 days. Then, their growth, behaviors, swimming performance, and metabolism were measured. Qingbo subjected to active hunting predator exposure exhibited decreased activity and predator inspection and improved fast-start escape performance compared to those in the control group. However, none of the parameters of the fish subjected to ambush predator exposure changed significantly. Fish subjected to mixed predator exposure exhibited improved fast-start escape performance but increased maintenance energy expenditure, whereas no changes were observed in any of the behavioral variables. Qingbo showed a stronger anti-predator response to active hunting predators than to ambush predators, suggesting that the fish exhibit a stronger anti-predator response to a current direct threat than to a potential threat (a predator exists nearby but seldom presents in attack behavior). Additionally, the response of prey fish to multiple predators was quite complex, and the coexistence and interaction of multiple predator species with different hunting modes may lead to serious stress responses and confound the prey's behavioral responses to each predator.

Sustained swimming exercise training decreases the individual variation in the metabolic phenotype of gilthead sea bream (Sparus aurata)

Cultured fish can be induced to swim, although the suitability and benefits remain to be tested. Sustained swimming exercise (SSE) training and detraining (DET) were applied in juvenile gilthead sea bream (Sparus aurata) and the metabolic rates were investigated. Fish with a total body mass of 80.5 ± 1.5 g and total length 17.2 ± 0.1 cm were maintained untrained (spontaneously swimming activity, UNT), swim-trained (induced sustained swimming activity, SSE) at 1 BL s^-1 for 28 days, or detrained (28 days of swimming followed by 10 days of untraining, DET). Standard metabolic rate (SMR), maximum metabolic rate (MMR), and excess post-exercise oxygen consumption (EPOC) were assessed (n = 10). In addition, the effects of SSE training (51 days) on blood and plasma parameters were investigated before and immediately after applying a high-intensity swimming (HIS) protocol. SMR, MMR, and EPOC values were not different between SSE, UNT, or DET fish (143.2, 465.5 mg O₂ kg^-1 h^-1, and 459.1 mg O₂ kg^-1, respectively). Spite the lack of differences between treatments, the dispersion in the residuals for SMR, MMR, and absolute aerobic scope (AAS) values followed the order UNT > DET > SSE, indicating that swim training decreases the individual variation of these metabolic parameters. Haematological parameters, plasma glucose, lactate, and cortisol levels were similar between SSE and UNT groups before HIS. Plasma glucose and lactate levels increased in both groups after HIS, being higher in the SSE group. Plasma cortisol levels were similar between both groups after HIS. Results suggest that SSE training improves energy use and reduces individual variation in SMR and MMR, an effect that declines with detraining.

Biochemical aspects of susceptibility to stressors in two small cyprinids Squalius laietanus and Barbus meridionalis from the NW Mediterranean

Specimens of two endemic cyprinids, Squalius laietanus (Catalan chub) and Barbus meridionalis (Mediterranean barbel), were sampled from a reference site in a small stream of the Ripoll River (NW Mediterranean) outside of their reproductive season. Biomarkers involved in xenobiotic-mediated responses were individually contrasted in fish of both species and 17 perfluoroalkyl substances (PFASs) analysed in muscle to reveal bioaccumulation trends. The parameters were in muscle: cholinesterases, metabolic lactate dehydrogenase (LDH) and citrate synthase (CS); and in liver: cytochrome P450 dependent activities (EROD and BFCOD), carboxylesterase (CE), glutathione S-transferase (GST), glutathione reductase (GR), glutathione peroxidase (GPX) and catalase (CAT). All markers are considered adaptive defence mechanism to face stress. Sensitivity to a model pesticide: dichlorvos was also contrasted in vitro in muscular acetylcholinesterase (AChE) and hepatic CE to reveal species sensitivity to neurotoxic chemicals. Enzymatic activities related to protective mechanisms such as butyrylcholinesterase (BuChE), CE and CAT were higher in chub whereas the antioxidant defences GR and GPX were higher in barbel. Aerobic CS was also higher in barbel while anaerobic LDH was so in chub. EROD activity did not differ between the two species but BFCOD activity was higher in barbel. Levels of PFAS were higher in barbel likely due to its benthic habitat. The in vitro tests revealed higher sensitivity to dichlorvos of muscular AChE in chub (lower IC50) which was probably compensated by a higher catalytic efficiency of CE. All these former biochemical particularities are discussed in terms of fish ecological performance in front of anthropogenic stressors.

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 (U_crit) and oxygen consumption rates (MO₂) were determined at different temperatures (13.2, 18.4, and 22.5 °C). The U_crit and MO₂ of different body mass (109.44, 175.74, and 249.42 g) fish were also obtained at 13.4 °C. The U_crit first increased as the temperature increased from 13.2 to 15.2 °C, which was calculated to be the optimal temperature for the U_crit, and then decreased with increasing temperature. The optimal swimming speed (U_opt) showed a similar trend to the U_crit. 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 U_crit and U_opt 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.

How do exercise training variables stimulate processes related to mitochondrial biogenesis in slow and fast trout muscle fibres?

NEW FINDINGS

What is the central question of this study? Exercise is known to promote mitochondrial biogenesis in skeletal muscle, but what are the most relevant training protocols to stimulate it? What is the main finding and its importance? As in mammals, training in rainbow trout affects slow and fast muscle fibres differently. Exercise intensity, relative to volume, duration and frequency, is the most relevant training variable to stimulate the processes related to mitochondrial biogenesis in both red and white muscles. This study offers new insights into muscle fibre type-specific transcription and expression of genes involved in mitochondrial adaptations following training.

ABSTRACT

Exercise is known to be a powerful way to improve health through the stimulation of mitochondrial biogenesis in skeletal muscle, which undergoes cellular and molecular adaptations. One of the current challenges in human is to define the optimal training stimulus to improve muscle performance. Fish are relevant models for exercise training physiology studies mainly because of their distinct slow and fast muscle fibres. Using rainbow trout, we investigated the effects of six different training protocols defined by manipulating specific training variables (such as exercise intensity, volume, duration and frequency), on mRNAs and some proteins related to four subsystems (AMP-activated protein kinase-peroxisome proliferator-activated receptor γ coactivator-1α signalling pathway, mitochondrial function, antioxidant defences and lactate dehydrogenase (LDH) metabolism) in both red and white muscles (RM and WM, respectively). In both muscles, high-intensity exercise stimulated more mRNA types and enzymatic activities related to mitochondrial biogenesis than moderate-intensity exercise. For volume, duration and frequency variables, we demonstrated fibre type-specific responses. Indeed, for high-intensity interval training, RM transcript levels are increased by a low training volume, but WM transcript responses are stimulated by a high training volume. Moreover, transcripts and enzymatic activities related to mitochondria and LDH show that WM tends to develop aerobic metabolism with a high training volume. For transcript stimulation, WM requires a greater duration and frequency of exercise than RM, whereas protein adaptations are efficient with a long training duration and a high frequency in both muscles.

Improved aerobic and anaerobic swimming performance after exercise training and detraining in Schizothorax wangchiachii: Implications for fisheries releases

Swimming performance (aerobic and anaerobic) is often used to predict the ability of fish to adapt and survive. Fish raised in captivity are typically poor swimmers and have lower survival rates than wild conspecifics when released into the natural environment. We investigated the potential for exercise training to enhance the swimming performance of Schizothorax wangchiachii held in captivity. Juvenile fish (mean body mass 1.40 ± 0.13 g, mean body length 4.36 ± 0.24 cm) were trained under five different regimes [3 cm·s^-1 control group (C), 10 cm·s^-1 for 6 (L6) and 12 h (L12) per day and 20 cm·s^-1 for 6 (H6) and 12 h (H12) per day] for 30 days and then detrained for 20 days (i.e. no training). Aerobic (i.e. critical swimming speed, U_crit), anaerobic swimming performance (i.e. endurance time at 1.2 or 1.5 U_crit), and morphological parameters were measured at the beginning (T₀), after 30 days of exercise training (T₃₀) and after 20 days of detraining (DT₂₀). Aerobic exercise training significantly improved the U_crit, endurance time at 1.2 and 1.5 U_crit of juvenile S. wangchiachii (P < .05). After 20 days of detraining, both the aerobic and anaerobic swimming performance of the H6 and H12 groups declined and no longer differed from the control group indicating a failure to maintain improved swimming performance, whereas improved swimming performance was maintained in L6 and L12 groups. No significant difference in swimming performance was found between 6 and 12 hours training at 10 cm·s^-1. Thus, exercise at close to 10 cm·s^-1 for 6 h per day for 30 days or a longer time periods prior to release appears to be a suitable regime for swimming performance enhancement, potentially increasing survivability of released S. wangchiachii in wild.

Sustained exercise-trained juvenile black carp (Mylopharyngodon piceus) at a moderate water velocity exhibit improved aerobic swimming performance and increased postprandial metabolic responses

The objectives of this study were to examine whether sustained exercise training at four water velocities, i.e. nearly still water (control), 1 body length (BL) s-1, 2 BL s-1 and 4 BL s-1, has effects on swimming performance and digestive metabolism in juvenile black carp (Mylopharyngodon piceus). The results demonstrated that fish subjected to sustained training at 2 and 4 BL s-1 showed significantly higher critical swimming speed (Ucrit) and maximum metabolic rate (MMR) over the control group. Fish subjected to sustained training at 1 and 2 BL s-1 showed a significantly (30 and 54%) prolonged duration, 14 and 17% higher postprandial ṀO2 increment (i.e. ṀO2peak), and 62 and 92% more energy expended on specific dynamic action (SDA), respectively, after consuming a similar meal over fish kept in nearly still water. These results suggest that (1) sustained exercise training at a higher speed (2 or 4 BL s-1) had a positive influence on the aerobic swimming performance of juvenile M. piceus, which may be associated with improved aerobic metabolism; and (2) sustained exercise training at a lower speed (1 or 2 BL s-1) resulted in elevated postprandial metabolic responses in juvenile M. piceus.

A comparison of constant acceleration swimming speeds when acceleration rates are different with critical swimming speeds in Chinese bream under two oxygen tensions

To investigate the effect of acceleration rates on the constant acceleration test speed (U cat) and to compare U cat with the critical swimming speed (U crit) in Chinese bream (Parabramis pekinensis), the U cat test at acceleration rates of 0.05, 0.1, 0.2, 0.4 and 0.8 cm s(-2) and the U crit test in juvenile fish at 20 °C in either normoxia (>90 % saturation oxygen tension) or hypoxia (30 % saturation) were compared. The lactate concentration ([lactate]) of white muscle, liver and plasma and the glycogen concentration ([glycogen]) of white muscle and liver were also measured to identify whether tissue substrate depletion or tissue lactate accumulation correlated with exhaustion. The U cat decreased with the acceleration rate, and there was no significant difference between U crit and U cat at lower acceleration rates. Hypoxia resulted in lower U cat and U crit, and the difference increased with decreased acceleration rates of the U cat test, possibly due to the increased contribution of aerobic components in U crit or U cat at low acceleration rates. Hypoxia elicited a significant decrease in muscle [glycogen] and an increase in muscle and liver [lactate] in resting fish. All post-exercise fish had similar muscle [lactate], suggesting that tissue lactate accumulation may correlate with exercise exhaustion. Unlike hypoxia, exercise induced an increase in muscle [lactate] and a significant increase in plasma [lactate], which were worthy of further investigation. The similar swimming speed and biochemical indicators after exercise in the U crit and U cat groups at low acceleration rates suggested that U cat can be an alternative for the more frequently adopted protocols in U crit in Chinese bream and possibly in other cyprinid fish species.

Adaptation and acclimation of aerobic exercise physiology in Lake Whitefish ecotypes (Coregonus clupeaformis)

The physiological mechanisms underlying local adaptation in natural populations of animals, and whether the same mechanisms contribute to adaptation and acclimation, are largely unknown. Therefore, we tested for evolutionary divergence in aerobic exercise physiology in laboratory bred, size-matched crosses of ancestral, benthic, normal Lake Whitefish (Coregonus clupeaformis) and derived, limnetic, more actively swimming "dwarf" ecotypes. We acclimated fish to constant swimming (emulating limnetic foraging) and control conditions (emulating normal activity levels) to simultaneously study phenotypic plasticity. We found extensive divergence between ecotypes: dwarf fish generally had constitutively higher values of traits related to oxygen transport (ventricle size) and use by skeletal muscle (percent oxidative muscle, mitochondrial content), and also evolved differential plasticity of mitochondrial function (Complex I activity and flux through Complexes I-IV and IV). The effects of swim training were less pronounced than differences among ecotypes and the traits which had a significant training effect (ventricle protein content, ventricle malate dehydrogenase activity, and muscle Complex V activity) did not differ among ecotypes. Only one trait, ventricle mass, varied in a similar manner with acclimation and adaptation and followed a pattern consistent with genetic accommodation. Overall, the physiological and biochemical mechanisms underlying acclimation and adaptation to swimming activity in Lake Whitefish differ.

Depletion of Essential Fatty Acids in the Food Source Affects Aerobic Capacities of the Golden Grey Mullet Liza aurata in a Warming Seawater Context

The objective of this study was to evaluate the combined effects of thermal acclimation and n-3 highly unsaturated fatty acids (n-3 HUFA) content of the food source on the aerobic capacities of fish in a thermal changing environment. The model used was the golden grey mullet Liza aurata, a species of high ecological importance in temperate coastal areas. For four months, fish were exposed to two food sources with contrasting n-3 HUFA contents (4.8% ecosapentaenoic acid EPA + docosahexaenoic acid DHA on the dry matter DM basis vs. 0.2% EPA+DHA on DM) combined with two acclimation temperatures (12°C vs. 20°C). The four experimental conditions were LH12, LH20, HH12 and HH20. Each group was then submitted to a thermal challenge consisting of successive exposures to five temperatures (9°C, 12°C, 16°C, 20°C, 24°C). At each temperature, the maximal and minimal metabolic rates, metabolic scope, and the maximum swimming speed were measured. Results showed that the cost of maintenance of basal metabolic activities was particularly higher when n-3 HUFA food content was low. Moreover, fish exposed to high acclimation temperature combined with a low n-3 HUFA dietary level (LH20) exhibited a higher aerobic scope, as well as a greater expenditure of energy to reach the same maximum swimming speed as other groups. This suggested a reduction of the amount of energy available to perform other physiological functions. This study is the first to show that the impact of lowering n-3 HUFA food content is exacerbated for fish previously acclimated to a warmer environment. It raises the question of the consequences of longer and warmer summers that have already been recorded and are still expected in temperate areas, as well as the pertinence of the lowering n-3 HUFA availability in the food web expected with global change, as a factor affecting marine organisms and communities.

Physiological plasticity to water flow habitat in the damselfish, Acanthochromis polyacanthus: linking phenotype to performance

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

Making Olympic lizards: the effects of specialised exercise training on performance

Exercise training is well known to affect a suite of physiological and performance traits in mammals, but effects of training in other vertebrate tetrapod groups have been inconsistent. We examined performance and physiological differences among green anole lizards (Anolis carolinensis) that were trained for sprinting or endurance, using an increasingly rigorous training regimen over 8 weeks. Lizards trained for endurance had significantly higher post-training endurance capacity compared with the other treatment groups, but groups did not show post-training differences in sprint speed. Although acclimation to the laboratory environment and training explain some of our results, mechanistic explanations for these results correspond with the observed performance differences. After training, endurance-trained lizards had higher haematocrit and larger fast glycolytic muscle fibres. Despite no detectable change in maximal performance of sprint-trained lizards, we detected that they had significantly larger slow oxidative muscle fibre areas compared with the other treatments. Treatment groups did not differ in the proportion of number of fibre types, nor in the mass of most limb muscles or the heart. Our results offer some caveats for investigators conducting training research on non-model organisms and they reveal that muscle plasticity in response to training may be widespread phylogenetically.

The effects of salinity on swimming performance of two estuarine fishes, Fundulus heteroclitus and Fundulus majalis

Prolonged and high-speed swimming performance measurements were used to explore the swimming abilities of two species of estuarine fishes, the mummichog Fundulus heteroclitus and the striped killifish Fundulus majalis, under different salinities. Critical swimming performance was significantly higher for F. majalis in high salinity than in low salinity, but no difference was observed in brief constant acceleration swimming trials in this species; however, the swimming performance of F. heteroclitus was not significantly affected by salinity changes, indicating that this species is well adapted to regular estuarine salinity oscillations. Fundulus majalis displayed higher swimming speeds than F. heteroclitus in both high and low salinities, and while this cannot be explained by their respective salinity preferences, the specific habitat preferences of F. majalis for sandy subtidal habitats and F. heteroclitus for vegetated marshes could explain the better swimming performance of F. majalis.

The life history of whole-organism performance

For almost 40 years, studies of whole-organism performance have formed a cornerstone of evolutionary physiology. Although its utility as a heuristic guide is beyond question, and we have learned much about morphological evolution from its application, the ecomorphological paradigm has frequently been applied to performance evolution in ways that range from unsatisfactory to inappropriate. More importantly, the standard ecomorphological paradigm does not account for tradeoffs among performance and other traits, nor between performance traits that are mediated by resource allocation. A revised paradigm that includes such tradeoffs, and the possible ways that performance and fitness-enhancing traits might affect each other, could potentially revivify the study of phenotypic evolution and make important inroads into understanding the relationships between morphology and performance and between performance and Darwinian fitness. We describe such a paradigm, and discuss the various ways that performance and key life-history traits might interact with and affect each other. We emphasize both the proximate mechanisms potentially linking such traits, and the likely ultimate factors driving those linkages, as well as the evolutionary implications for the overall, multivariate phenotype. Finally, we highlight several research directions that will shed light on the evolution and ecology of whole-organism performance and related life-history traits.

Predator-driven intra-species variation in locomotion, metabolism and water velocity preference in pale chub (Zacco platypus) along a river

Fish inhabit environments that vary greatly in terms of predation intensity, and these predation regimes are generally expected to be a major driver of divergent natural selection. To test whether there is predator-driven intra-species variation in the locomotion, metabolism and water velocity preference of pale chub (Zacco platypus) along a river, we measured unsteady and steady swimming and water velocity preference among fish collected from both high- and low-predation habitats in the Wujiang River. We also measured the routine metabolic rate (RMR), maximum metabolic rate (MMR) and cost of transport (COT) and calculated the optimal swimming speed (Uopt). The fish from the high-predation populations showed a shorter response latency, elevated routine metabolism, lower swimming efficiency at low swimming speed and lower water velocity preference compared with those from the low-predation populations. Neither of the kinematic parameters fast-start and critical swimming speed (Ucrit) showed a significant difference between the high- and low-predation populations. The fish from the high-predation populations may improve their predator avoidance capacity primarily through an elevated routine metabolism and shorter response latency to achieve advanced warning and escape, rather than an improved fast-start swimming speed or acceleration. Thus, the cost of this strategy is an elevated RMR, and no trade-off between unsteady and steady swimming performance was observed in the pale chub population under various predation stresses. It was interesting to find that the high-predation fish showed an unexpected lower velocity preference, which might represent a compromise between predation avoidance, foraging and energy saving.