Condition, prolonged swimming performance and muscle metabolic capacities of cod Gadus morhua

Feeding frequency does not interact with BPA exposure to influence metabolism or behaviour in zebrafish (Danio rerio)

Resource limitation can constrain energy (ATP) production, and thereby affect locomotion and behaviour such as exploration of novel environments and boldness. Consequently, ecological processes such as dispersal and interactions within and between species may be influenced by food availability. Energy metabolism, and behaviour are regulated by endocrine signalling, and may therefore be impacted by endocrine disrupting compounds (EDCs) including bisphenol A (BPA) derived from plastic manufacture and pollution. It is important to determine the impacts of these novel environmental contexts to understand how human activity alters individual physiology and behaviour and thereby populations. Our aim was to determine whether BPA exposure interacts with feeding frequency to alter metabolism and behaviour. In a fully factorial experiment, we show that low feeding frequency reduced zebrafish (Danio rerio) mass, condition, resting metabolic rates, total distance moved and speed in a novel arena, as well as anxiety indicated by the number of times fish returned to a dark shelter. However, feeding frequency did not significantly affect maximal metabolic rates, aerobic scope, swimming performance, latency to leave a shelter, or metabolic enzyme activities (citrate synthase and lactate dehydrogenase). Natural or anthropogenic fluctuation in food resources can therefore impact energetics and movement of animals with repercussions for ecological processes such as dispersal. BPA exposure reduced LDH activity and body mass, but did not interact with feeding frequency. Hence, behaviour of adult fish is relatively insensitive to disruption by BPA. However, alteration of LDH activity by BPA could disrupt lactate metabolism and signalling and together with reduction in body mass could affect size-dependent reproductive output. BPA released by plastic manufacture and pollution can thereby impact conservation and management of natural resources.

Fish shrinking, energy balance and climate change

A decline in size is increasingly recognised as a major response by ectothermic species to global warming. Mechanisms underlying this phenomenon are poorly understood but could include changes in energy balance of consumers, driven by declines in prey size coupled with increased energy demands due to warming. The sardine Sardina pilchardus is a prime example of animal shrinking, European populations of this planktivorous fish are undergoing profound decreases in body condition and adult size. This is apparently a bottom-up effect coincident with a shift towards increased reliance on smaller planktonic prey. We investigated the hypothesis that foraging on smaller prey would lead to increased rates of energy expenditure by sardines, and that such expenditures would be exacerbated by warming temperature. Using group respirometry we measured rates of energy expenditure indirectly, as oxygen uptake, by captive adult sardines offered food of two different sizes (0.2 or 1.2 mm items) when acclimated to two temperatures (16 °C or 21 °C). Energy expenditure during feeding on small items was tripled at 16 °C and doubled at 21 °C compared to large items, linked to a change in foraging mode between filter feeding on small or direct capture of large. This caused daily energy expenditure to increase by ~10 % at 16 °C and ~40 % at 21 °C on small items, compared to large items at 16 °C. These results support that declines in prey size coupled with warming could influence energy allocation towards life-history traits in wild populations. This bottom-up effect could partially explain the shrinking and declining condition of many small pelagic fish populations and may be contributing to the shrinking of other fish species throughout the marine food web. Understanding how declines in prey size can couple with warming to affect consumers is a crucial element of projecting the consequences for marine fauna of ongoing anthropogenic global change.

Tissue Distribution of mtDNA Copy Number And Expression Pattern of An mtDNA-Related Gene in Three Teleost Fish Species

Teleosts are the most speciose vertebrates and have diverse swimming performance. Based on swimming duration and speed, teleosts are broadly divided into sustained, prolonged, and burst swimming fish. Teleosts with different swimming performance have different energy requirements. In addition, energy requirement also varies among different tissues. As mitochondrial DNA (mtDNA) copy number is correlated with ATP production, we speculated that mtDNA copy number varies among fish with different swimming performance, as well as among different tissues. In other species, mtDNA copy number is regulated by tfam (mitochondrial transcription factor A) through mtDNA compaction and mito-genome replication initiation. In order to clarify the tissue distribution of mtDNA copy number and expression pattern of tfam in teleosts with disparate swimming performance, we selected representative fish with sustained swimming (Pseudocaranx dentex), prolonged swimming (Takifugu rubripes), and burst swimming (Paralichthys olivaceus). We measured mtDNA copy number and tfam gene expression in 10 tissues of these three fish. The results showed the mtDNA content pattern of various tissues was broadly consistent among three fish, and high-energy demanding tissues contain higher mtDNA copy number. Slow-twitch muscles with higher oxidative metabolism possess a greater content of mtDNA than fast-twitch muscles. In addition, relatively higher mtDNA content in fast-twitch muscle of P. olivaceus compared to the other two fish could be an adaptation to their frequent burst swimming demands. And the higher mtDNA copy number in heart of P. dentex could meet their oxygen transport demands of long-distance swimming. However, tfam expression was not significantly correlated with mtDNA copy number in these teleosts, suggesting tfam may be not the only factor regulating mtDNA content among various tissues. This study can lay a foundation for studying the role of mtDNA in the adaptive evolution of various swimming ability in teleost fish.

Bioenergetics modelling of growth processes in parasitized Eastern Baltic cod (Gadus morhua L.)

Changes in physiological processes can reveal how individuals respond to environmental stressors. It can be difficult to link physiological responses to changes in vital rates such as growth, reproduction and survival. Here, bioenergetics modelling can aid in understanding non-intuitive outcomes from stressor combinations. Building on an established bioenergetics model, we examine the potential effects of parasite infection on growth rate and body condition. Parasites represent an overlooked biotic factor, despite their known effects on the physiology of the host organism. As a case study, we use the host-parasite system of Eastern Baltic cod (Gadus morhua) infected with the parasitic nematode Contraceacum osculatum. Eastern Baltic cod have during the past decade experienced increasing infection loads with C. osculatum that have been shown to lead to physiological changes. We hypothesized that infection with parasites affects cod growth negatively as previous studies reveal that the infections lead to reduced energy turnover, severe liver disease and reduced nutritional condition. To test this, we implemented new variables into the bioenergetics model representing the physiological changes in infected fish and parameterized these based on previous experimental data. We found that growth rate and body condition decreased with increased infection load. Highly infected cod reach a point of no return where their energy intake cannot maintain a surplus energy balance, which may eventually lead to induced mortality. In conclusion, parasite infections cannot be ignored when assessing drivers of fish stock dynamics.

Exploring the impacts of different fasting and refeeding regimes on Nile tilapia (Oreochromis niloticus L.): growth performance, histopathological study, and expression levels of some muscle growth-related genes

The current study investigated how different fasting and refeeding regimes would impact Nile tilapia growth performance, histopathological examination, and gene expression of myostatin, myogenin, GH, IGF-1, and NPYa. Nile tilapia fish (n = 120) were randomly allocated into four groups, including the control group fed on a basal diet for 6 weeks (F6), group A starved for 1 week and then refed for 5 weeks (S1F5), group B starved for 2 weeks and then refed for 4 weeks (S2F4), while group C starved for 4 weeks and then refed for 2 weeks (S4F2). Fasting provoked a decrease in body weight coincided with more extended starvation periods. Also, it induced muscle and liver histological alterations; the severity was correlated with the length of fasting periods. Gene expression levels of GH, MSTN, MYOG, and NPYa were significantly increased, while IGF1 was markedly depressed in fasted fish compared to the control group. Interestingly, refeeding after well-planned short fasting period (S1F5) modulated the histopathological alterations. To some extent, these changes were restored after refeeding. Restored IGF-I and opposing fasting expression profiles of the genes mentioned above thus recovered weights almost like the control group and achieved satisfactory growth compensation. Conversely, refeeding following more extended fasting periods failed to restore body weight. In conclusion, refeeding after fasting can induce a compensatory response. Still, the restoration capacity is dependent on the length of fasting and refeeding periods through exhibiting differential morphological structure and expressions pattern for muscle and growth-related genes.

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 (U_crit) and sustained (4 hours at 80% U_crit) 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 U_crit 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 (ṀO₂), indicating strictly aerobic swimming efforts. At low swimming speeds ṀO₂ 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 ṀO₂ became similar to fed fish showing that maximum metabolic rates were maintained. The changes in ṀO₂ 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 ṀO₂ 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.

Investigating food limitations in wild fisheries: Estuarine fish form dynamic aggregations around a supplementary feeding station and increase localised secondary productivity

Whether wild fish populations are food limited in some inshore and estuarine marine ecosystems is an area of increasing research and focus. To investigate this phenomenon, the abundance and behaviours of fish in a temperate South Pacific estuary were observed in response to the provision of supplementary feed. Observations were conducted over 120-weeks, involving a 60-week period over which fish were actively fed followed by a 60 week without feeding. During active feeding, estuarine associated fish (primarily yellow-eyed mullet Aldrichetta forsteri) showed a highly predictable pattern of fish abundance, biomass and behavioural formation coinciding with the almost daily feeder operation. Tidal current velocities and turbidity appeared to have little influence on the attendance and formations of fish over this period, although season did influence some variables. Peaking at close to 9000 individual fish and 880 kg biomass, fish attendance during the operation of the feeding station was markedly higher than during the period when the feed station was no longer active. Whereby only 0-100 individuals were typically present, and fish no longer showed collective behavioural formations. A direct result of the large number of fish aggregating on this feeding station was an increase in the secondary productivity of the observable zone around the feeding station. Whereby secondary productivity increased by a factor of ∼30 above that observed when the feed station was not operating. Supplementary feeding effectively transformed the study site - a highly modified intertidal location - from an area of very low productivity to one comparable with highly productive temperate estuary environments described elsewhere. The behavioural drivers and ecological relevance of these observations are discussed.

Growth, body condition and contest performance after early-life food restriction in a long-lived tropical fish

Adverse conditions during early life can cause lasting body size deficits with effects on social and sexual competition, while an accelerated growth response can allow animals to catch up in body size but can be physiologically costly as well. How animals balance growth deficits and growth compensation is predicted to depend on the effects of each on lifetime fitness. We investigated the effects of experimental early-life food restriction on growth, body condition, and adult contest competition in a cichlid fish (Tropheus sp.). Their longevity and aseasonal breeding suggest that, with view on lifetime reproductive success, temporarily growth-restricted Tropheus should rather invest extra time in reaching competitive body size than risk the potential costs of accelerated growth. However, size-selective predation pressure by gape size-limited piscivores may have favored the evolution of an accelerated growth response to early-life delays. Experimentally food-restricted fish temporarily reduced their growth rate compared to a control group, but maintained their body condition factor at the control level throughout the 80-week study period. There was no evidence for an accelerated growth response following the treatment, as the food-restricted fish never exceeded the size-specific growth rates that were measured in the control group. Food-restricted fish caught up with the body size of the control group several months after the end of the treatment period and were as likely as control fish to win size-matched contests over territories. Regardless of feeding regime, there were sex-specific differences in growth rates and in the trajectories of condition factors over time. Females grew more slowly than males but maintained their condition factors at a high level throughout the study period, whereas the males' condition factors declined over time. These differences may reflect sex-specific contributions of condition and body size to adult fitness that are associated with female mouthbrooding and male competition for breeding territories.

Is starvation a cause of overmortality of the Mediterranean sardine?

Animal mortality is difficult to observe in marine systems, preventing a mechanistic understanding of major drivers of fish population dynamics. In particular, starvation is known to be a major cause of mortality at larval stages, but adult mortality is often unknown. In this study, we used a laboratory food-deprivation experiment, on wild caught sardine Sardina pilchardus from the Gulf of Lions. This population is interesting because mean individual phenotype shifted around 2008, becoming dominated by small, young individuals in poor body condition, a phenomenon that may result from declines in energy availability. Continuous monitoring of body mass loss and metabolic rate in 78 captive food-deprived individuals revealed that sardines could survive for up to 57 days on body reserves. Sardines submitted to long-term caloric restriction prior to food-deprivation displayed adaptive phenotypic plasticity, reducing metabolic energy expenditure and enduring starvation for longer than sardines that had not been calorie-restricted. Overall, entry into critical fasting phase 3 occurred at a body condition of 0.72. Such a degree of leanness has rarely been observed over 34 years of wild population monitoring. Still, the proportion of sardines below this threshold has doubled since 2008 and is maximal in January and February (the peak of the reproductive season), now reaching almost 10 % of the population at that time. These results indicate that the demographic changes observed in the wild may result in part from starvation-related adult mortality at the end of the winter reproductive period, despite adaptive plastic responses.

Artificial light at night interacts with predatory threat to alter reef fish metabolite profiles

Light cycles and predatory threat define activity patterns (e.g. feeding/sleeping, activity/rest) in most diurnal fish species. Artificial light at night (ALAN) may disrupt natural cycles and biochemical processes, a mismatch which can eventually reduce condition and fitness. We evaluate the separate and joint effects of ALAN and predator threat on metabolism within brain, liver and muscle tissue of a common, wild caught damselfish, blue green chromis (Chromis viridis). The effects of ALAN varied according to tissue type and predator exposure. In all tissues we observed changes in metabolic pathways associated with increased activity under continuous light (despite provision of shelter), specifically those associated with energy metabolism, cell signalling, responses to oxidative stress and markers of cellular damage. In both the brain and liver tissues, predator threat served to moderate the influence of ALAN on metabolic change, likely due to increased sheltering behaviour. However, no interaction of predator threat with ALAN was observed in metabolism of the muscle tissue. Our results highlight complex sub-acute effects of ALAN exposure on tissue specific and whole organism energy metabolism. Collectively these effects indicate that ALAN has significant scope to reduce fitness of coastal fishes and potentially threaten ecosystem services, but that these changes are highly complex and may be altered by biotic drivers of activity.

Limits on performance and survival of juvenile sockeye salmon (Oncorhynchus nerka) during food deprivation: a laboratory-based study

Long-distance migrations can be energetically demanding and can represent phases of high mortality. Understanding relationships between body condition and migratory performance can help illuminate the challenges and vulnerabilities of migratory species. Juvenile anadromous sockeye salmon (Oncorhynchus nerka) may migrate over 1000 km from their freshwater nursery habitats to estuary and ocean feeding grounds. During the period corresponding to the seaward migration of sockeye salmon, we held smolts in the laboratory to ask the following: (i) Does non-feeding migration duration influence prolonged swim performance and survival? (ii) What are the relationships between individual body condition and swim performance and survival? Wild sockeye salmon were intercepted during their migration and held without food for up to 61 days to represent the non-feeding freshwater migration and the extremes of poor estuary habitat. We conducted 40 sets of prolonged swim trials on 319 fish from 3 treatment groups that represented entrance to the marine environment on (i) an average,(ii) a delayed and (iii) a severely delayed migration schedule. Experimentally controlled freshwater migration duration did not impact swim performance or survival. Swim performance decreased concomitant with condition factor, where smolts with a Fulton's condition factor of <0.69 were less likely (<50% probability) to complete the swim test (90 min swim test, at ~0.50 m/s). Survival of salmon smolts in the laboratory was less likely at energy densities of less than 3.47 MJ/kg. Swim performance decreased much sooner than survival, suggesting that swim performance, and therefore condition factor, may be a good indicator of survival of migratory smolts, as fish with reduced swim performance will likely be predated. These two relationships, one more ecologically relevant and one more clinical, help reveal the limits of long-distance migration for juvenile salmon and can be used to determine population-specific starvation risk associated with various freshwater and marine habitat conditions.

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 (U_crit) 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 U_crit 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.

Bisphenols alter thermal responses and performance in zebrafish (Danio rerio)

Plastic pollutants are novel environmental stressors that are now persistent components of natural ecosystems. Endocrine disrupting chemicals such as bisphenols that leach out of plastics can modify physiological responses of animals by interfering with hormone signalling. Here, we tested whether three commonly produced bisphenols, bisphenol A (BPA), bisphenol F (BPF) and bisphenol S (BPS), impair thermal acclimation of swimming performance and metabolic enzyme [citrate synthase (CS) and lactate dehydrogenase (LDH)] activities in adult zebrafish (Danio rerio). We found that exposure to 30-μg l-1 BPF and BPS, but not BPA, reduced swimming performance, and no interactions between bisphenol exposure and acclimation (3 weeks to 18°C and 28°C) or acute test (18°C and 28°C) temperatures were found. BPA interacted with acclimation and acute test temperatures to determine CS activity, an indicator of mitochondrial density and aerobic metabolic capacity. BPS reduced CS activity and an interaction (at a one-tailed significance) between acclimation temperature and BPF exposure determined CS activity. LDH activity reflects anaerobic ATP production capacity, and BPA and BPF altered the effects of thermal acclimation and acute test temperatures on LDH activity. Our data show that all bisphenols we tested at ecologically relevant concentrations can disrupt the thermal responses of fish. BPS and BPF are used as environmentally safer alternatives to BPA, but our data show that these bisphenols are also of concern, particularly in thermally variable environments.

Physiological condition of Eastern Baltic cod, Gadus morhua, infected with the parasitic nematode Contracaecum osculatum

Establishing relationships between parasite infection and physiological condition of the host can be difficult and therefore are often neglected when describing factors causing population declines. Using the parasite-host system between the parasitic nematode Contracaecum osculatum and the Eastern Baltic cod Gadus morhua, we here shed new light on how parasite load may relate to the physiological condition of a transport host. The Eastern Baltic cod is in distress, with declining nutritional conditions, disappearance of the larger fish, high natural mortality and no signs of recovery of the population. During the latest decade, high infection levels with C. osculatum have been observed in fish in the central and southern parts of the Baltic Sea. We investigated the aerobic performance, nutritional condition, organ masses, and plasma and proximate body composition of wild naturally infected G. morhua in relation to infection density with C. osculatum. Fish with high infection densities of C. osculatum had (i) decreased nutritional condition, (ii) depressed energy turnover as evidenced by reduced standard metabolic rate, (iii) reduction in the digestive organ masses, and alongside (iv) changes in the plasma, body and liver composition, and fish energy source. The significantly reduced albumin to globulin ratio in highly infected G. morhua suggests that the fish suffer from a chronic liver disease. Furthermore, fish with high infection loads had the lowest Fulton's condition factor. Yet, it remains unknown whether our results steam from a direct effect of C. osculatum, or because G. morhua in an already compromised nutritional state are more susceptible towards the parasite. Nevertheless, impairment of the physiological condition can lead to reduced swimming performance, compromising foraging success while augmenting the risk of predation, potentially leading to an increase in the natural mortality of the host. We hence argue that fish-parasite interactions must not be neglected when implementing and refining strategies to rebuild deteriorating populations.

Prolonged fasting followed by refeeding modifies proteome profile and parvalbumin expression in the fast-twitch muscle of pacu (Piaractus mesopotamicus)

Here, we analyzed the fast-twitch muscle of juvenile Piaractus mesopotamicus (pacu) submitted to prolonged fasting (30d) and refeeding (6h, 24h, 48h and 30d). We measured the relative rate of weight and length increase (RRI_length and RRI_weight), performed shotgun proteomic analysis and did Western blotting for PVALB after 30d of fasting and 30d of refeeding. We assessed the gene expression of igf-1, mafbx and pvalb after 30d of fasting and after 6h, 24h, 48h and 30d of refeeding. We performed a bioinformatic analysis to predict miRNAs that possibly control parvalbumin expression. After fasting, RRI_length, RRI_weight and igf-1 expression decreased, while the mafbx expression increased, which suggest that prolonged fasting caused muscle atrophy. After 6h and 24h of refeeding, mafbx was not changed and igf-1 was downregulated, while after 48h of refeeding mafbx was downregulated and igf-1 was not changed. After 30d of refeeding, RRI_length and RRI_weight were increased and igf-1 and mafbx expression were not changed. Proteomic analysis identified 99 proteins after 30d of fasting and 71 proteins after 30d of refeeding, of which 23 and 17, respectively, were differentially expressed. Most of these differentially expressed proteins were related to cytoskeleton, muscle contraction, and metabolism. Among these, parvalbumin (PVALB) was selected for further validation. The analysis showed that pvalb mRNA was downregulated after 6h and 24h of refeeding, but was not changed after 30d of fasting or 48h and 30d of refeeding. The Western blotting confirmed that PVALB protein was downregulated after 30d of fasting and 30d of refeeding. The downregulation of the protein and the unchanged expression of the mRNA after 30d of fasting and 30d of refeeding suggest a post-transcriptional regulation of PVALB. Our miRNA analysis predicted 444 unique miRNAs that may target pvalb. In conclusion, muscle atrophy and partial compensatory growth caused by prolonged fasting followed by refeeding affected the muscle proteome and PVALB expression.

Effects of freezing on length and mass measurements of Atlantic cod Gadus morhua in the Baltic Sea

An aggregated sample of 925 Atlantic cod Gadus morhua collected by four countries in different regions of the Baltic Sea during different seasons were measured (total length, L_T = 161-890 mm and weighed (mass, M = 45-6900 g) both before freezing and after defrosting. The cod were found to decrease significantly in both L_T and M following death and frozen storage. There was an average (±SD) change in L_T of -2.91% (±0.05%) following freezing, independent of starting L_T . Total M changed by -2.65% (±0.14%), independent of starting mass. Shrinkage of L_T and M did not differ significantly between 1 and 4 months frozen storage, though L_T shrinkage was significantly greater after 1 or 4 months in the freezer compared with after 5 days. There was significant variation in L_T and M shrinkage between regions of capture. A significant negative relationship between condition of cod and L_T or M change was also observed. Equations to back-calculate fresh L_T and M from thawed L_T , M and standard length (L_S ), gutted L_T , gutted L_S and gutted M are provided.

Influence of a dynamic rearing environment on development of metabolic phenotypes in age-0 Lake Sturgeon, Acipenser fulvescens

Environment-phenotype interactions are the most pronounced during early life stages and can strongly influence metabolism and ultimately ecological fitness. In the present study, we examined the effect of temperature [ambient river temperature (ART) vs ART+2°C], dissolved oxygen (DO; 100% vs 80%) and substrate (presence vs absence) on standard metabolic rate, forced maximum metabolic rate and metabolic scope with Fulton's condition factor (K), energy density (ED) and critical thermal maximum (CTmax) in age-0 Lake Sturgeon, Acipenser fulvescens, before and after a simulated overwintering event. We found that all the environmental variables strongly influenced survival, K, ED and CTmax. Fish reared in elevated temperature showed higher mortality and reduced K pre-winter at 127 days post-hatch (dph). Interestingly, we did not find any significant difference in terms of metabolic rate between treatments at both sampling points of pre- and post-winter. Long-term exposure to 80% DO reduced ED in Lake Sturgeon post-winter at 272 dph. Our data suggest that substrate should be removed at the onset of exogenous feeding to enhance the survival rate of age-0 Lake Sturgeon in the first year of life. Effects of early rearing environment during larval development on survival over winter are discussed with respect to successful recruitment of stock enhanced Lake Sturgeon, a species that is at risk throughout its natural range.

Thermal biology and swimming performance of Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus)

Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) are two commercially important marine fishes impacted by both overfishing and climate change. Increasing ocean temperatures are affecting the physiology of these species and causing changes in distribution, growth, and maturity. While the physiology of cod has been well investigated, that of haddock has received very little attention. Here, we measured the metabolic response to increasing temperatures, as well as the critical thermal maximum (CT_max), of cod acclimated to 8 and 12 °C and haddock acclimated to 12 °C. We also compared the swimming performance (critical swimming speed, U_crit) of cod and haddock at 12 °C, as well as the U_crit of 12 °C-acclimated cod acutely exposed to a higher-than-optimal temperature (16 °C). The CT_max for cod was 21.4 and 23.0 °C for 8- and 12 °C-acclimated fish, respectively, whereas that for the 12 °C-acclimated haddock was 23.9 °C. These values were all significantly different and show that haddock are more tolerant of high temperatures. The aerobic maximum metabolic rate (MMR) of swimming cod remained high at 16 °C, suggesting that maximum oxygen transport capacity was not limited at a temperature above optimal in this species. However, signs of impaired swimming (struggling) were becoming evident at 16 °C. Haddock were found to reach a higher U_crit than cod at 12 °C (3.02 vs. 2.62 body lengths s⁻¹, respectively), and at a lower MMR. Taken together, these results suggest that haddock perform better than cod in warmer conditions, and that haddock are the superior swimmer amongst the two species.

Habitat Partitioning and its Possible Genetic Background Between Two Sympatrically Distributed Eel Species in Taiwan

The geographical distributions of the Japanese eel (Anguilla japonica) and Giant-mottled eel (A. marmorata) overlap in many regions in East Asia and therefore suffer from interspecific competition in the same rivers. After a long period of adaptation, the Japanese eel and Giant-mottled eel may exhibit habitat partitioning in the rivers to diminish the interspecific competition between them. In this study, we conducted a field investigation in the Fengshan River in Taiwan to survey the habitat distributions of the Japanese eel and Giant-mottled eel throughout a river. Moreover, we investigated whether their habitat distributions are related to their swimming and upstream migration. Thus, the mRNA expression levels of several candidate genes that may be associated with the swimming and upstream migration of eel were examined in the glass eels of the Japanese eel and Giant-mottled eel. Field investigation indicated that the Japanese eel mainly inhabited the lower and middle reaches of the Fengshan River, but the Giant- mottled eel was distributed over the middle to upper reaches. The mRNA expression levels of fMYH, dio2, gria3, and neurod1 were higher in the Giant-mottled eel than in the Japanese eel, implying that Giant- mottled eels might have better swimming bursts and more active upstream migration than Japanese eels. These results suggest that there is a habitat partition at which these two eel species coexist in a river, and their habitat distributions may be linked to their swimming bursts and upstream migration. Determining the habitat distributions of freshwater eels is important for developing applicable plans for eel conservation and resource management.

Ocean warming combined with lower omega-3 nutritional availability impairs the cardio-respiratory function of a marine fish

Highly unsaturated fatty acids of the omega-3 series (HUFA) are major constituents of cell membranes, yet are poorly synthesised de novo by consumers. Their production, mainly supported by aquatic microalgae, has been decreasing with global change. The consequences of such reductions may be profound for ectotherm consumers, as temperature tightly regulates the HUFA content in cell membranes, maintaining their functionality. Integrating individual, tissue and molecular approaches, we examined the consequences of the combined effects of temperature and HUFA depletion on the key cardio-respiratory functions of the golden grey mullet, an ectotherm grazer of high ecological importance. For 4 months, fish were exposed to two contrasting HUFA diets [4.8% eicosapentaenoic acid (EPA)+docosahexaenoic acid (DHA) on dry matter (DM) versus 0.2% EPA+DHA on DM] at 12 and 20°C. Ventricular force development coupled with gene expression profiles measured on cardiac muscle suggest that combining HUFA depletion with warmer temperatures leads to: (1) a proliferation of sarcolemmal and sarcoplasmic reticulum Ca²⁺ channels and (2) a higher force-generating ability by increasing extracellular Ca²⁺ influx via sarcolemmal channels when the heart has to sustain excessive effort due to stress and/or exercise. At the individual scale, these responses were associated with a greater aerobic scope, maximum metabolic rate and net cost of locomotion, suggesting the higher energy cost of this strategy. This impaired cardiac performance could have wider consequences for other physiological performance such as growth, reproduction or migration, all of which greatly depend on heart function.

Reduced Swimming Performance Repeatedly Evolves on Loss of Migration in Landlocked Populations of Alewife

Whole-organism performance tasks are accomplished by the integration of morphological traits and physiological functions. Understanding how evolutionary change in morphology and physiology influences whole-organism performance will yield insight into the factors that shape its own evolution. We demonstrate that nonmigratory populations of alewife (Alosa pseudoharengus) have evolved reduced swimming performance in parallel, compared with their migratory ancestor. In contrast to theoretically and empirically based predictions, poor swimming among nonmigratory populations is unrelated to the evolution of osmoregulation and occurs despite the fact that nonmigratory alewives have a more fusiform (torpedo-like) body shape than their ancestor. Our results suggest that elimination of long-distance migration from the life cycle has shaped performance more than changes in body shape and physiological regulatory capacity.

Effects of acute temperature and salinity changes, body length and starvation on the critical swimming speed of juvenile tiger puffer, Takifugu rubripes

The critical swimming speed (U _crit, cm s^-1) of juvenile tiger puffer Takifugu rubripes was determined under different temperatures (15, 21, 25 and 30 °C), salinities (5, 10, 20, 32 and 40), body lengths (3.32, 4.08, 5.06 and 5.74 cm) and starvation days (1, 3, 6 and 9 days). Acute temperature change, body length and starvation significantly influenced the U _crit of tiger puffers, whereas acute salinity change had no significant effect. The U _crit increased as the temperature increased from 15 to 30 °C. The U _crit increased as the body length increased from 3.32 to 5.74 cm, whereas relative critical swimming speed (U _crit', body length s^-1) decreased. The relationship between the body length (l, cm) and U _crit or U _crit' can be described by the quadratic model as U _crit = - 1.4088 l ² + 16.976 l - 11.64, R ² = 0.9698 (P < 0.01) or U _crit' = - 0.1937 l ² + 0.9504 l + 7.7666, R ² = 0.9493 (P < 0.01). The U _crit decreased as starvation days increased from 1 to 9 days. Low temperature and starvation can reduce the swimming ability of juvenile tiger puffers. Results can be of value in evaluating the swimming ability of juvenile tiger puffers, understanding ecological processes and improving the population enhancement of tiger puffers.

Short-term feed and light deprivation reduces voluntary activity but improves swimming performance in rainbow trout Oncorhynchus mykiss

Rainbow trout Oncorhynchus mykiss (~ 180 g, 16 °C and < 5 kg m^-3) that were feed deprived and kept in total darkness showed a significant increase in critical swimming speed (U _crit) between 1 and 12 days of deprivation (from 3.35 to 4.46 body length (BL) s^-1) with no increase in maximum metabolic rate (MMR). They also showed a significant decrease in the estimated metabolic rate at 0 BL s^-1 over 12 days which leads to a higher factorial aerobic metabolic scope at day 12 (9.38) compared to day 1 (6.54). Routine metabolic rates were also measured in ~ 90 g rainbow trout that were swimming freely in large circular respirometers at 16 °C. These showed decreasing consumption oxygen rates and reductions in the amount of oxygen consumed above standard metabolic rate (a proxy for spontaneous activity) over 12 days, though this happened significantly faster when they were kept in total darkness when compared to a 12:12-h light-dark (LD) photoperiod. Weight loss during this period was also significantly reduced in total darkness (3.33% compared to 4.98% total body weight over 12 days). Immunological assays did not reveal any consistent up- or downregulation of antipathogenic and antioxidant enzymes in the serum or skin mucus of rainbow trout between 1 and 12 days of feed and light deprivation. Overall, short periods of deprivation do not appear to significantly affect the performance of rainbow trout which appear to employ a behavioural energy-sparing strategy, albeit more so in darkness than under a 12:12-h LD regime.

Measuring Ucrit and endurance: equipment choice influences estimates of fish swimming performance

This study compared the critical swimming speed (U_crit ) and endurance performance of three Australian freshwater fish species in different swim-test apparatus. Estimates of U_crit measured in a large recirculating flume were greater for all species compared with estimates from a smaller model of the same recirculating flume. Large differences were also observed for estimates of endurance swimming performance between these recirculating flumes and a free-surface swim tunnel. Differences in estimates of performance may be attributable to variation in flow conditions within different types of swim chambers. Variation in estimates of swimming performance between different types of flumes complicates the application of laboratory-based measures to the design of fish passage infrastructure.

Functional modularity in lake-dwelling characin fishes of Mexico

Modular evolution promotes evolutionary change, allowing independent variation across morphological units. Recent studies have shown that under contrasting ecological pressures, patterns of modularity could be related to divergent evolution. The main goal of the present study was to evaluate the presence of modular evolution in two sister lacustrine species, Astyanax aeneus and A. caballeroi, which are differentiated by their trophic habits. Two different datasets were analyzed: (1) skull X-rays from 73 specimens (35 A. aeneus and 38 A. caballeroi) to characterize skull variation patterns, considering both species and sex effects. For this dataset, three different modularity hypotheses were tested, previously supported in other lacustrine divergent species; (2) a complete body shape dataset was also tested for four modularity hypotheses, which included a total of 196 individuals (110 Astyanax aeneus and 86 A. caballeroi). Skull shape showed significant differences among species and sex (P < 0.001), where Astyanax caballeroi species showed an upwardly projected mandible and larger preorbital region. For the skull dataset, the modularity hypothesis ranked first included three partitioning modules. While for the complete body dataset the best ranked hypothesis included two modules (head vs the rest of the body), being significant only for A. caballeroi.

Intraspecific differences in endurance swim performance and cardiac size in sockeye salmon (Oncorhynchus nerka) parr tested at three temperatures

Pacific salmon encounter widely varying environmental conditions across populations. Performance traits and environmental tolerance limits are predicted to be related to the typical abiotic and biotic conditions encountered by each population. Endurance swim performance at three different temperatures (8, 12, 22 °C) was compared across nine populations of sockeye salmon (Oncorhynchus nerka (Walbaum, 1792)) parr from British Columbia, Canada, reared in a common laboratory environment. In addition, relative ventricular mass (RVM) was compared between good and poor performers from each population. Populations significantly differed in endurance swim performance and these differences were related to the natal lake environment. Specifically, parr populations that reside in warm, shallow lakes (Okanagan, Scotch, and Stellako) had superior swim performance at 12 °C compared with 8 °C. All other populations from deeper, cooler lakes had equivalent swim performance at 8 and 12 °C. Individual variability in swim performance within a population was not due to differences in cardiac size. Similarly, RVM did not vary across parr populations, suggesting that population differences in swim performance were not associated with cardiac size. This study provides further support that sockeye salmon parr are locally adapted to their environmental conditions.

Regional asymmetry of metabolic and antioxidant profile in the sciaenid fish shi drum (Umbrina cirrosa) white muscle. Response to starvation and refeeding

The objective of the present study is to characterize the metabolic and antioxidant profile of white muscle of shi drum in two sites of the body, anterior dorsal (AM) and posterior dorsal (PM) portions. In addition, it will be analyzed the possible effect of starvation and a subsequent refeeding, with two different protocols, pair feeding and ad libitum. Activities of key enzymes of intermediary metabolism and of antioxidant enzymes, as well as lipid peroxidation, as an index of oxidative stress, were evaluated. The results indicate the existence of a regional asymmetry of the metabolic capacities of the white muscle of shi drum, which is likely related to the different contribution to swimming of the body regions examined. Starvation induces a metabolic depression that is more marked in those activities that support burst swimming in PM, while those activities supporting maintenance requirements are conserved. The greatest energy demands during starvation appear to lie in AM, which showed the highest oxidative metabolism rate. The increased use of fatty acids as energy source for AM leads to oxidative stress. A period of more than four weeks of refeeding for full restoration of metabolic capacities in AM is needed, probably related to the higher muscle mass located in this region. On the contrary, all enzyme activities in PM returned to control levels in both refeeding protocols, but pair feeding seems to be advantageous since compensatory growth has been taking place without signs of oxidative stress. This work was addressed to gain knowledge on the physiology of a promising fish species in aquaculture like shi drum. The results displayed here show how the starving and further re-feeding events could generate oxidative stress situations characterized by high lipid peroxidation levels which may influence negatively on the quality of the edible part of the fish. This study opens an interesting field on this fish species which deserves being investigated in the future.

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Research on the metabolism of a new fish species with potential aquaculture practices is depicted.

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Starving and refeeding promote different metabolic alterations depending on body region of white muscle.

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Fasting and refeeding may influence the quality of the edible part of the fish.

An approach to incorporate individual personality in modeling fish dispersal across in-stream barriers

Animal personalities are an important factor that affects the dispersal of animals. In the context of aquatic species, dispersal modeling needs to consider that most freshwater ecosystems are highly fragmented by barriers reducing longitudinal connectivity. Previous research has incorporated such barriers into dispersal models under the neutral assumption that all migrating animals attempt to ascend at all times. Modeling dispersal of animals that do not perform trophic or reproductive migrations will be more realistic if it includes assumptions of which individuals attempt to overcome a barrier. We aimed to introduce personality into predictive modeling of whether a nonmigratory invasive freshwater fish (the round goby, Neogobius melanostomus) will disperse across an in‐stream barrier. To that end, we experimentally assayed the personalities of 259 individuals from invasion fronts and established round goby populations. Based on the population differences in boldness, asociability, and activity, we defined a priori thresholds with bolder, more asocial, and more active individuals having a higher likelihood of ascent. We then combined the personality thresholds with swimming speed data from the literature and in situ measurements of flow velocities in the barrier. The resulting binary logistic regression model revealed probabilities of crossing a barrier which depended not only on water flow and fish swimming speed but also on animal personalities. We conclude that risk assessment through predictive dispersal modeling across fragmented landscapes can be advanced by including personality traits as parameters. The inclusion of behavior into modeling the spread of invasive species can help to improve the accuracy of risk assessments.

Effect of sustained training on glycolysis and fatty acids oxidation in swimming muscles and liver in juvenile tinfoil barb Barbonymus schwanenfeldii (Bleeker, 1854)

The present study examines the effect of sustained exercise on glycolysis and fatty acids oxidation in the swimming muscles and liver in juvenile tinfoil barb (Barbonymus schwanenfeldii). The subjects were divided into one control group (water current speed of 0.0 bl s^-1, body length per second) and two training groups (1.0 and 2.0 bl s^-1), respectively. Results showed that the glycolysis was stimulated by high-speed training in the white muscle, accompanied by significantly increased activities of hexokinase, pyruvate kinase, and reduction in glycogen contents in training groups (P < 0.05). On the contrary, the extreme fatty acids oxidation was observed in the red muscle in high-speed training group, showed significant reduction in crude lipid content with a significant increase in the activities of hormone-sensitive lipase, β-hydroxyacyl-CoA dehydrogenase, and cytochrome C oxidase in 2.0 bl s^-1 group (P < 0.05). In addition, the saturated fatty acids in the red muscle and monounsaturated fatty acids in the white muscle were used preferentially during sustained training, respectively. Furthermore, the glycogen content within the liver was also significantly reduced with increasing training intensities (P < 0.05). These results suggested that glycogen and fatty acids were all used as a fuel to support sustained swimming in two functional muscles in B. schwanenfeldii, but higher glycolysis and fatty acids oxidation were seen in white and red muscles during high-speed swimming, respectively. Furthermore, the hepatic glycogen played an important role in the supply of energy in sustained training periods in B. schwanenfeldii.

Silvering and swimming effects on aerobic metabolism and reactive oxygen species in the European eel

Silvering, the last metamorphosis in the eel life cycle induces morphological and physiological modifications in yellow eels (sedentary stage). It pre-adapts them to cope with the extreme conditions they will encounter during their 6000-km spawning migration. A previous study showed that silver eels are able to cope with reactive oxygen species (ROS) over-production linked to an increase in aerobic metabolism during sustained swimming, but the question remains as to whether this mechanism is associated with silvering. A sustained swimming session decreased red muscle in vitro mitochondrial oxygen consumption (MO₂) but increased ROS production in both eel stages. The swimming exercise used here was perhaps too intense to induce a stimulation of mitochondrial function or biogenesis even when antioxidant enzyme activities were unchanged. Pro-oxidant/antioxidant imbalance by lipid peroxidation increased in yellow but significantly decreased in silver eels. The silvering process therefore appears to allow a pre-adaptation of red muscle radical metabolism to the demands of spawning migration.

The effects of starvation and re-feeding on growth and swimming performance of juvenile black carp (Mylopharyngodon piceus)

We investigated the effects of starvation and re-feeding on growth and swimming performance and their relationship in juvenile black carp (Mylopharyngodon piceus). We measured the specific growth rate (SGR), resting metabolic rate (RMR) and constant acceleration test speed (U CAT, the maximum swimming speed at exhaustion by constant acceleration test with 0.1667 cm s(-2) rate) in a treatment group (21 days of starvation then 21 days of re-feeding) and control group (routine feeding) (n = 20). Starvation resulted in a 17 % decrease in body mass of black carp (P < 0.05). After 21 days of re-feeding, body mass was greater than that of pre-starvation but still less than that of the control group at 42 days. During the re-feeding phase, the SGR of the treatment group was higher than that of the control group (P < 0.05). Starvation resulted in a significant decrease in the RMR and U CAT. After 21 days of re-feeding, both the RMR and U CAT recovered to the pre-starvation levels. In the control group, individual juvenile black carp displayed strong repeatability of the RMR and U CAT across the measurement periods (P ≤ 0.002). In the treatment group, RMR showed significant repeatability between pre-starvation and re-feeding (P = 0.007), but not between pre-starvation and starvation or between starvation and re-feeding. U CAT showed significant repeatability between pre-starvation and starvation (P = 0.006) and between pre-starvation and re-feeding (P = 0.001), but not between starvation and re-feeding. No correlation or only a weak correlation was found between any two variables of RMR, U CAT and SGR, whereas the increment of the U CAT (ΔU CAT) was negatively correlated with that of SGR during the starvation phase (r = -0.581, n = 20, P = 0.007) and re-feeding phase (r = -0.568, n = 20, P = 0.009). This suggested that within individual black carp, there is a trade-off between growth and maintenance (or development) of swimming performance under food-limited conditions.

The effects of starvation on fast-start escape and constant acceleration swimming performance in rose bitterling (Rhodeus ocellatus) at two acclimation temperatures

To investigate the effects of starvation and acclimation temperature on the escape ability of juvenile rose bitterling (Rhodeus ocellatus), we measured the fast-start escape and constant acceleration swimming performance of fish fasted for 0 (control), 1 and 2 weeks and half-lethal periods (6 or 4 weeks) at two temperatures (15 and 25 °C). Fish acclimated at a high temperature exhibited shorter response latency (R), higher maximum linear velocity (V max) and longer escape distance during escape movement (D 120ms) than those at the low temperature. Starvation resulted in a significant decrease in V max and D 120ms at either low or high temperature and a significant increase in R at only the high temperature in the half-lethal period groups (P < 0.05). The relationship between V max (Y, m s(-1)) and starvation time (X, week) was Y 15 = -0.062X + 1.568 (r = -0.665, n = 36, P < 0.001) at low temperature and Y 25 = -0.091X + 1.755 (r = -0.391, n = 40, P = 0.013) at high temperature. The relationship between U cat (Y, cm s(-1)) and starvation time (X, week) was Y 15 = -1.649X + 55.418 (r = -0.398, n = 34, P = 0.020) at low temperature and Y 25 = -4.917X + 62.916 (r = -0.793, n = 33, P < 0.001) at high temperature. The slopes of equations showed a significant difference between low and high temperature (F 1,63 = 9.688, P = 0.003), which may be due to the different energy substrate utilization when faced with food deprivation at different temperatures.

Effects of Loma morhua (Microsporidia) infection on the cardiorespiratory performance of Atlantic cod Gadus morhua (L)

The microsporidian Loma morhua infects Atlantic cod (Gadus morhua) in the wild and in culture and results in the formation of xenomas within the gill filaments, heart and spleen. Given the importance of the two former organs to metabolic capacity and thermal tolerance, the cardiorespiratory performance of cod with a naturally acquired infection of Loma was measured during an acute temperature increase (2 °C h(-1)) from 10 °C to the fish's critical thermal maximum (CT(Max)). In addition, oxygen consumption and swimming performance were measured during two successive critical swimming speed (U(crit)) tests at 10 °C. While Loma infection had a negative impact on cod cardiac function at warm temperatures, and on metabolic capacity in both the CT(Max) and U(crit) tests (i.e. a reduction of 30-40%), it appears that the Atlantic cod can largely compensate for these Loma-induced cardiorespiratory limitations. For example, (i) CT(Max) (21.0 ± 0.3 °C) and U(crit) (~1.75 BL s(-1)) were very comparable to those reported in previous studies using uninfected fish from the same founder population; and (ii) our data suggest that tissue oxygen extraction, and potentially the capacity for anaerobic metabolism, is enhanced in fish infected with this microsporidian.

Short-term exposure to municipal wastewater influences energy, growth, and swimming performance in juvenile Empire Gudgeons (Hypseleotris compressa)

Effectively treating domestic wastewater is paramount for preserving the health of aquatic ecosystems. Various technologies exist for wastewater treatment, ranging from simple pond-based systems to advanced filtration, and it is important to evaluate the potential for these different options to produce water that is acceptable for discharge. Sub-lethal responses were therefore assessed in juvenile Empire Gudgeons (Hypseleotris compressa) exposed for a period of two weeks to control, 12.5, 25, 50, and 100% wastewater treated through a multi-stage constructed wetland (CW) treatment system. Effects on basic energy reserves (i.e., lipids and protein), growth and condition, and swimming performance were quantified following exposure. A significant increase in weight and condition was observed in fish exposed to 50 and 100% wastewater dilutions, whereas whole-body lipid content was significantly reduced in these treatments. Maximum swimming velocity increased in a dose-dependent manner amongst treatment groups (although not significantly), whereas angular velocity was significantly reduced in the 50 and 100% dilutions. Results demonstrate that treated domestic wastewater can influence the growth and swimming performance of fish, and that such effects may be related to alterations to primary energy stores. However, studies assessing complex wastewaters present difficulties when it comes to interpreting responses, as many possible factors can contribute towards the observed effects. Future research should address these uncertainties by exploring interaction between nutrients, basic water quality characteristics and relevant contaminant mixtures, for influencing the energetics, growth, and functional performance of aquatic animals.

The potential impacts of migratory difficulty, including warmer waters and altered flow conditions, on the reproductive success of salmonid fishes

Climate change and urbanisation of watercourses affect water temperatures and current flow velocities in river systems on a global scale. This represents a particularly critical issue for migratory fish species with complex life histories that use rivers to reproduce. Salmonids are migratory keystone species that provide substantial economical value to ecosystems and human societies. Consequently, a comprehensive understanding of the effects of environmental stressors on their reproductive success is critical in order to ensure their continued abundance during future climatic change. Salmonids are capital breeders, relying entirely on endogenous energy stores to fuel return migration to their natal spawning sites and reproduction upon arrival. Metabolic rates and cost of transport en-route increase with temperature and at extreme temperatures, swimming is increasingly fuelled anaerobically, resulting in an oxygen debt and reduced capacity to recover from exhaustive exercise. Thermally challenged salmonids also produce less viable gametes, which themselves are affected by water temperature after release. Passage through hydrological barriers and temperature changes both affect energy expenditure. As a result, important energetic tradeoffs emerge between extra energy used during migration and that available for other facets of the reproductive cycle, such as reproductive competition and gamete production. However, studies identifying these tradeoffs are extremely sparse. This review focuses on the specific locomotor responses of salmonids to thermal and hydrological challenges, identifying gaps in our knowledge and highlighting the potential implications for key aspects of their reproduction.

Climbing experience in glass eels: A cognitive task or a matter of physical capacities?

The European eel is a panmictic species, whose decline has been recorded since the last 30 years. Among human-induced environmental factors of decline, the impact of water dams during species migration is questioned. Indeed, water impoundments can be a severe obstacle for young eels trying to reach the upstream freshwater zones, even if they are equipped with fish-friendly passes. The passage by such devices could be an important event shaping the outcome of the future life and life history traits of eels. We studied what phenotypic traits were associated with the event of experience of passage by water obstacles. We analyzed specific enzyme activities and/or gene transcription levels in the muscle and brain to test whether the obstacle passage is rather a physical or cognitive task. We found that after a long period of maintenance under homogenous conditions, transcription levels of several genes linked to synaptic plasticity, neurogenesis and thyroid activity differed among the field-experience groups. In contrast, muscle gene transcription levels or enzymatic activities did not show any differences among fish groups. We suggest that cognitive processes such as learning and memory acquisition rather than swimming-related metabolic capacities are involved in passage of water obstacles by young eels.

Effects of fasting and feeding on the fast-start swimming performance of southern catfish Silurus meridionalis

This study investigated the effects of fasting and feeding on the fast-start escape swimming performance of juvenile southern catfish Silurus meridionalis, a sit-and-wait forager that encounters extreme fasting and famine frequently during its lifespan. Ten to 30 days of fasting resulted in no significant change in most of the variables measured in the fast-start response except a 20-30% decrease in the escape distance during the first 120 ms (D_120ms ) relative to the control group (48 h after feeding). The ratio of the single-bend (SB) response (lower energetic expenditure) to the double-bend (DB) response increased significantly from 0% in the control group to 75 and 82·5% in the 20 and 30 day fasting groups, respectively. Satiated feeding (25% of body mass) resulted in a significantly lower (36·6%) maximum linear velocity (V_max ) and a significantly lower (43·3%) D_120ms than in non-fed fish (control group, 48 h after feeding). Half-satiated feeding (12·5% of body mass), however, showed no significant effects on any of the measured variables of the fast-start response relative to control fish. It is suggested that the increase in the ratio of SB:DB responses with fasting in S. meridionalis may reflect a trade-off between energy conservation and maintaining high V_max , while variables of fast-start performance were more sensitive to feeding than fasting might be an adaptive strategy to their foraging mode and food availability in their habitat.

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.

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

To investigate the effect of prolonged exercise training on swimming performance and the underlying biochemical mechanisms in juvenile common carp (Cyprinus carpio), we measured the critical swimming speed (Ucrit), the excess post-exercise oxygen consumption (EPOC), the activity of red and white muscle enzymes [pyruvate kinase (PK), lactate dehydrogenase (LDH) and citrate synthase (CS)], the tissue substrates (glycogen and glucose content of muscle and liver) and metabolite (the lactate content of plasma and muscle) content of exercise-trained (60% Ucrit for 4 weeks) and non-trained fish. We also measured the biochemical indices of both trained and non-trained fish immediately after Ucrit, after exhaustive exercise and 1h after exhaustive exercise. The aerobic swimming performance, as indicated by Ucrit, increased significantly after exercise training, most likely because of the higher tissue metabolic capacity, as suggested by the higher CS activity in the red muscle tissue, and the higher energy store and more efficient substrate utilization, as suggested by higher liver and muscle glycogen contents at rest but lower tissue glycogen contents after Ucrit. The lower lactate content after Ucrit is most likely because of higher aerobic metabolic capacity, and (or) the clearance rate of lactate in trained fish may also contribute to improved aerobic swimming performance. Compared to Ucrit, exhaustive exercise elicited higher plasma and muscle lactate contents. The anaerobic metabolic performance is not affected by the exercise training, as suggested by the EPOC. However, trained fish did show higher lactate clearance rates, as suggested by lower muscle lactate content after a 1h recovery period following exhaustive exercise compared to non-trained fish. Furthermore, trained fish decreased their liver and muscle glycogen contents more profoundly after exhaustive exercise, suggesting that training can improve the substrate utilization during anaerobic exercise.

Short periods of fasting followed by refeeding change the expression of muscle growth-related genes in juvenile Nile tilapia (Oreochromis niloticus)

Muscle growth mechanisms are controlled by molecular pathways that can be affected by fasting and refeeding. In this study, we hypothesized that short period of fasting followed by refeeding would change the expression of muscle growth-related genes in juvenile Nile tilapia (Oreochromis niloticus). The aim of this study was to analyze the expression of MyoD, myogenin and myostatin and the muscle growth characteristics in the white muscle of juvenile Nile tilapia during short period of fasting followed by refeeding. Juvenile fish were divided into three groups: (FC) control, feeding continuously for 42 days, (F5) 5 days of fasting and 37 days of refeeding, and (F10) 10 days of fasting and 32 days of refeeding. At days 5 (D5), 10 (D10), 20 (D20) and 42 (D42), fish (n=14 per group) were anesthetized and euthanized for morphological, morphometric and gene expression analyses. During the refeeding, fasted fish gained weight continuously and, at the end of the experiment (D42), F5 showed total compensatory mass gain. After 5 and 10 days of fasting, a significant increase in the muscle fiber frequency (class 20) occurred in F5 and F10 compared to FC that showed a high muscle fiber frequency in class 40. At D42, the muscle fiber frequency in class 20 was higher in F5. After 5 days of fasting, MyoD and myogenin gene expressions were lower and myostatin expression levels were higher in F5 and F10 compared to FC; at D42, MyoD, myogenin and myostatin gene expression was similar among all groups. In conclusion, this study showed that short periods of fasting promoted muscle fiber atrophy in the juvenile Nile tilapia and the refeeding caused compensatory mass gain and changed the expression of muscle growth-related genes that promote muscle growth. These fasting and refeeding protocols have proven useful for understanding the effects of alternative warm fish feeding strategies on muscle growth-related genes.

The effects of hypoxia acclimation, exercise training and fasting on swimming performance in juvenile qingbo (Spinibarbus sinensis)

To investigate the effects of hypoxia acclimation, exercise training and fasting on the swimming performance of juvenile qingbo (Spinibarbus sinensis), we measured the critical swimming speed (U (crit)), resting and excess post-exercise oxygen consumption (EPOC) of control, hypoxia-acclimated, exercise-acclimated and fasting fish at 25°C. The muscle and plasma metabolites before and after a bout of exhaustive exercise (produced by chasing) were also measured. The fish were acclimated to hypoxia (48 h at 1.0 mg L(-1), 12.5% air saturation), exercise training (2 weeks at 60% of U (crit), 6 h daily) or fasting (2 weeks). All treatments resulted in significantly lower resting oxygen consumption ([Formula: see text]O(2rest)) but had no effect on the magnitude of EPOC. Hypoxia acclimation had no effect on U (crit) or peak post-exercise oxygen consumption ([Formula: see text]O(2peak)) but produced a higher depletion of muscle [glycogen] post-chasing (P < 0.05). Exercise training produced a significant increase in U (crit), higher liver [glycogen] pre-chasing and higher depletion of muscle [glycogen] post-chasing. Fasting resulted in a significant decrease in U (crit), [Formula: see text]O(2peak), muscle and liver [glycogen]. These results suggested that hypoxia acclimation had no effect on swimming performance in qingbo. Exercise training produced improved swimming performance by increasing the stored energy and the metabolic capacity of muscle. Fasting had a profound effect on swimming performance through both decreased respiratory capacity and a depleted energy store.

Variability in swimming performance and underlying physiology in rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta)

We investigated intra- and interspecific variation in swimming performance and related physiological parameters in two members of the salmonid family. For our comparisons, we sourced juvenile brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) from one hatchery and a second strain of rainbow trout from another. The hatcheries maintain genetic stocks obtained several decades ago from very different environments. We tested competing hypotheses: that there would be greater interspecific (across species) variation or that there would be greater intraspecific (within species) variation, owing to regional adaptations. To test these hypotheses, individual and small schools of five fish were taken to fatigue using the critical swimming speed test (U(crit)), and three post-exercise physiological metrics, packed red cell volume (hematocrit), citrate synthase and lactate dehydrogenase activity, were assessed. The majority of the results in swimming performance and hematocrit support that intraspecific variation was greater than interspecific variation, i.e. the location had a stronger effect than did genus. Variation in lactate dehydrogenase activity supported neither intra- nor interspecific variation as determining factors. In sum, our findings suggest that the performance of different species of salmonids from the same locale can be more similar than those of the same species from different areas.

Swimming performance trade-offs across a gradient in community composition in Trinidadian killifish (Rivulus hartii)

The impacts of predation and competition on life history, behavioral, and morphological traits are well established for many organisms, but effects on locomotor performance have received relatively little attention. We examined variation in sprint speed and critical swimming speed (U(crit), a measure of stamina) in the Trinidadian killifish (Rivulus hartii) across a gradient of ecological communities. R. hartii are located in (1) "high-predation" sites with large, piscine piscivores, (2) "Rivulus-guppy" sites with guppies, and (3) "Rivulus-only" sites with only R. hartii. R. hartii suffer higher mortality in high-predation sites. In Rivulus-guppy sites, population densities are reduced and growth rates increased compared with Rivulus-only sites, which likely represent indirect effects of guppy predation on young R. hartii. We show a significant negative relationship, suggesting a trade-off, between sprint speed and endurance; Rivulus from high-predation sites were faster sprinters but had reduced critical swimming speeds. This trade-off was also apparent in correlations of the nine population means. At the individual level, the correlation was weaker and only significantly negative when all nine populations (three from each site) were pooled and values were not corrected for body size. Sex had a significant effect on U(crit), with females having a lower U(crit), but sexes did not differ in sprint speed. Fish from high-predation sites also exhibited increased tail lengths and fineness ratios compared to sites without large predators. The two low-predation sites showed no statistical differences in locomotor performance or morphology.