The effects of acclimation to reversed seasonal temperatures on the swimming performance of adult brown trout Salmo trutta

The impacts of diel thermal variability on growth, development and performance of wild Atlantic salmon (Salmo salar) from two thermally distinct rivers

Temperature in many natural aquatic environments follows a diel cycle, but to date, we know little on how diel thermal cycles affect fish biology. The current study investigates the growth, development and physiological performance of wild Atlantic salmon collected from the Miramichi and Restigouche rivers (NB, Canada). Fish were collected as parr and acclimated to either 16-21 or 19-24°C diel thermal cycles throughout the parr and smolt life stages. Both Miramichi and Restigouche Atlantic salmon parr grew at similar rates during 16-21 or 19-24°C acclimations. However, as smolts, the growth rates of the Miramichi (-8% body mass day-1) and Restigouche (-38% body mass day-1) fish were significantly slower at 19-24°C, and were in fact negative, indicating loss of mass in this group. Acclimation to 19-24°C also increased Atlantic salmon CTmax. Our findings suggest that both life stage and river origin impact Atlantic salmon growth and performance in the thermal range used herein. These findings provide evidence for local adaptation of Atlantic salmon, increased vulnerability to warming temperatures, and highlight the differential impacts of these ecologically relevant diel thermal cycles on the juvenile life stages in this species.

Climate change and anadromous fish: How does thermal acclimation affect the mechanics of the myotomal muscle of the Atlantic salmon, Salmo salar?

In response to accelerated temperature shifts due to climate change, the survival of many species will require forms of thermal acclimation to their changing environment. We were interested in how climate change will impact a commercially and recreationally important species of fish, Atlantic salmon (Salmo salar). As climate change alters the thermal environment of their natal streams, we asked how their muscle function will be altered by extended exposure to both warm and cold temperatures. We performed a thermal acclimation study of S. salar muscle mechanics of both fast-twitch, or white, and slow-twitch, or red, myotomal muscle bundles to investigate how temperature acclimated Atlantic salmon would respond across a range of different temperatures. Isometric contraction properties, maximum shortening velocity, and oscillatory power output were measured and compared amongst three groups of salmon-warm acclimated (20°C), cold-acclimated (2°C), and those at their rearing temperature (12°C). The Atlantic salmon showed limited thermal acclimation in their contraction kinetics, and some of the shifts in contractile properties that were observed would not be predicted to mitigate the impact of a warming environment. For instance, the maximum shortening velocity at a common test temperature was higher in the warm acclimated group and lower in the cold-acclimated group. In addition, critical swimming speed did not vary with temperature of acclimation when tested at a common temperature (12°C). Our results suggest that Atlantic salmon populations will continue to struggle in response to a warming environment.

Mismatched light and temperature cues disrupt locomotion and energetics via thyroid-dependent mechanisms

Animals integrate information from different environmental cues to maintain performance across environmental gradients. Increasing average temperature and variability induced by climate change can lead to mismatches between seasonal cues. We used mosquitofish (Gambusia holbrooki) to test the hypotheses that mismatches between seasonal temperature and light regimes (short days and warm temperature and vice versa) decrease swimming performance, metabolic rates and mitochondrial efficiency and that the responses to light and temperature are mediated by thyroid hormone. We show that day length influenced thermal acclimation of swimming performance through thyroid-dependent mechanisms. Oxygen consumption rates were influenced by acclimation temperature and thyroid hormone. Mitochondrial substrate oxidation rates (state three rates) were modified by the interaction between temperature and day length, and mitochondrial efficiency (P/O ratios) increased with warm acclimation. Using P/O ratios to calibrate metabolic (oxygen consumption) scope showed that oxygen consumption did not predict adenosine triphosphate (ATP) production. Unlike oxygen consumption, ATP production was influenced by day length in a thyroid-dependent manner. Our data indicate that oxygen consumption alone should not be used as a predictor of ATP production. Overall, the effects of thyroid hormone on locomotion and energetics were reversed by mismatches such as warm temperatures on short days. We predict that mid to high latitudes in North America and Asia will be particularly affected by mismatches as a result of high seasonality and predicted warming over the next 50 years.

Thermal acclimation of rainbow trout myotomal muscle, can trout acclimate to a warming environment?

Climate change is a looming threat to the planet. Cold-water aquatic species will face significant physiological challenges due to elevated summer temperatures. Salmonids, such as rainbow trout (Oncorhynchus mykiss) maintain fidelity to native streams, limiting their ability to mitigate the impact of climate change through migration. We examined how rainbow trout swimming performance and muscle function were shaped by the thermal environment. We hypothesized that trout would show slower muscle contractile properties and slower swimming performance with long-term exposure to warmer water. For fish held at either 10 °C or 20 °C, maximum steady swimming speed (U_crit) was determined, and contractile properties of both fast-twitch (white) and slow-twitch (red) myotomal muscle were examined. In addition, immunohistochemistry and quantitative PCR were used to assess changes in myosin content of the myotomal muscle in response to holding temperature. Rainbow trout exposed to warm water for six weeks displayed relatively limited thermal acclimation response. When tested at a common temperature (10 °C), 20 °C acclimated fish had modestly slower muscle performance compared to 10 °C acclimated fish. Significant differences in swimming performance and muscle contractile properties were primarily at colder test temperatures (e.g. 2 °C for muscle mechanics). Shifts in myosin heavy chain protein composition and myosin heavy chain gene expression in the swimming muscle were observed in white but not red muscle. Our results suggest that rainbow trout will have a limited ability to mitigate elevated environmental temperature through thermal acclimation of their myotomal or swimming muscle.

Red muscle function and thermal acclimation to cold in rainbow smelt, Osmerus mordax, and rainbow trout, Oncorhynchus mykiss

Climate change affects the thermal environment of aquatic organisms. Changes in the thermal environment may affect muscle function in the eurythermal rainbow smelt, Osmerus mordax, and relatively more stenothermal rainbow trout, Oncorhynchus mykiss. Literature suggests that the trout will be more sensitive to changes in environmental temperature, as they experience a more limited range of environmental temperatures. To examine the effects of thermal environment on red muscle function, both the smelt and trout were thermally acclimated to either a warm (12-15°C) or cold (4-5°C) temperature, after which studies of swimming performance and muscle mechanics were performed. The data on swimming performance and maximum muscle shortening velocity in rainbow smelt were previously published. In both species, cold-acclimated (CA) fish swam with a significantly faster maximum aerobic swimming speed than warm-acclimated fish, when tested at a common temperature of 10°C. Similarly, CA smelt and trout had faster red muscle contraction kinetics. However, smelt displayed a greater shift in contractile properties, such as having a significant shift in maximum muscle shortening velocity that was not observed in trout. The smelt red muscle outperformed trout, with twitch and tetanic times of relaxation being significantly faster for CA smelt compared with CA trout, especially when contraction kinetics were tested at 2°C. The smelt shows a greater thermal acclimation response compared with trout, with more robust increases in maximum swimming speed and faster muscle contractile properties. These differences in acclimation response may contribute to understanding how smelt and trout cope with climate change.

The effect of thermal acclimation on aerobic scope and critical swimming speed in Atlantic salmon, Salmo salar

The Atlantic salmon is extensively studied owing to conservation concerns and its economic importance in aquaculture. However, a thorough report of their aerobic capacity throughout their entire thermal niche has not been described. In this study, Atlantic salmon (∼450 g) were acclimated for 4 weeks at 3, 8, 13, 18 or 23°C, and then tested in a large Brett-type swimming respirometer in groups of 10 per trial. Both standard metabolic rate and active metabolic rate continued to increase with temperature, which resulted in an aerobic scope that also increased with temperature, but was statistically similar between 13, 18 and 23°C. The critical swimming speed peaked at 18°C (93.1±1.2 cm s^-1), and decreased significantly at the extreme temperatures to 74.8±0.5 and 84.8±1.6 cm s^-1 at 3 and 23°C, respectively. At 23°C, the accumulated mortality reached 20% over 4 weeks, while no fish died during acclimation at colder temperatures. Furthermore, fish at 23°C had poor appetite and lower condition factor despite still having a high aerobic scope, suggesting that oxygen uptake was not the limiting factor in the upper thermal niche boundary. In conclusion, Atlantic salmon were able to maintain a high aerobic capacity and good swimming capabilities throughout the entire thermal interval tested, thus demonstrating a high level of flexibility in respiratory capacity towards different temperature exposures.

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.

Intraspecific individual variation of temperature tolerance associated with oxygen demand in the European sea bass (Dicentrarchus labrax)

The European sea bass (Dicentrarchus labrax) is an economically important fish native to the Mediterranean and Northern Atlantic. Its complex life cycle involves many migrations through temperature gradients that affect the energetic demands of swimming. Previous studies have shown large intraspecific variation in swimming performance and temperature tolerance, which could include deleterious and advantageous traits under the evolutionary pressure of climate change. However, little is known of the underlying determinants of this individual variation. We investigated individual variation in temperature tolerance in 30 sea bass by exposing them to a warm temperature challenge test. The eight most temperature-tolerant and eight most temperature-sensitive fish were then studied further to determine maximal swimming speed (U CAT), aerobic scope and post-exercise oxygen consumption. Finally, ventricular contractility in each group was determined using isometric muscle preparations. The temperature-tolerant fish showed lower resting oxygen consumption rates, possessed larger hearts and initially recovered from exhaustive exercise faster than the temperature-sensitive fish. Thus, whole-animal temperature tolerance was associated with important performance traits. However, the temperature-tolerant fish also demonstrated poorer maximal swimming capacity (i.e. lower U CAT) than their temperature-sensitive counterparts, which may indicate a trade-off between temperature tolerance and swimming performance. Interestingly, the larger relative ventricular mass of the temperature-tolerant fish did not equate to greater ventricular contractility, suggesting that larger stroke volumes, rather than greater contractile strength, may be associated with thermal tolerance in this species.

Variations in temperature acclimation effects on glycogen storage, hypoxia tolerance and swimming performance with seasonal acclimatization in juvenile Chinese crucian carp

The aim of this study was to test whether temperature acclimation (10 vs 20 °C) effects on tissue glycogen content, hypoxia tolerance, and swimming performance of Chinese crucian carp (Carassius auratus) varied with seasonal acclimatization (winter vs spring) and potential combined interactions. Both the routine metabolic rate (MO(2rout)) and critical oxygen tension (P(crit)) of the MO(2rout) increased significantly with temperature, whereas the seasonal acclimatization showed no significant effect. Only the high temperature group that acclimatized in spring showed a significantly higher aquatic surface respiration (ASR(crit)) value compared with the other three groups. Fish in spring tended to show ASR behavior at higher oxygen tension compared with those in winter, which might have been caused by a more active lifestyle. Time to show LOE prolonged by 25-34% under low temperature. Spring fish showed 20% shorter LOE duration at 10 °C, whereas the difference tended to vanish at 20 °C. Glycogen contents in both liver and muscle were higher in winter than spring. The liver and muscle glycogen content decreased by 5-42% after exposure to anoxic conditions, whereas the magnitude was much smaller in spring. When fish swam in normoxic conditions, fish in higher temperatures showed higher critical swimming speed (Ucrit) than low temperature (5.49 vs 3.74 BL s(-1) in winter and 4.27 vs 3.21 BL s(-1) in spring), whereas fish in winter also showed higher U(crit) than fish in spring for each temperature. However, when fish swam in hypoxic waters, fish in higher temperatures showed a more profound decrease (52-61%) in U(crit) compared to those in lower temperature (25-27%). Fish in lower temperatures that had acclimatized in winter showed the highest U(crit), which might have been caused by higher glycogen storage. The present study suggested that both glycogen storage and alterations in lifestyle had profound effects on hypoxia tolerance and swimming performance, which resulted in a profound difference between seasons and acclimation temperatures.

Physiological, cellular and biochemical thermal stress response of intertidal shrimps with different vertical distributions: Palaemon elegans and Palaemon serratus

The ability to cope with high temperature variations is a critical factor in intertidal communities. Two species of intertidal rocky shore shrimps (Palaemon sp.) with different vertical distributions were collected from the Portuguese coast in order to test if they were differentially sensitive to thermal stress. Three distinct levels of biological organization (organismal, biochemical, and cellular) were surveyed. The shrimp were exposed to a constant rate of temperature increase of 1°C x h(-1), starting at 20°C until reaching the CTMax (critical thermal maximum). During heat stress, two biomarkers of protein damage were quantified in the muscle via enzyme-linked immunosorbent assays: heat shock proteins HSP70 (hsp70/hsc70) and total ubiquitin. Muscle histopathological alterations caused by temperature were also evaluated. CTMax values were not significantly different between the congeners (P. elegans 33.4 ± 0.5 °C; P. serratus 33.0 ± 0.5 °C). Biomarker levels did not increase along the temperature trial, but P. elegans (higher intertidal) showed higher amounts of HSP70 and total ubiquitin than P. serratus (lower intertidal). HSP70 and total ubiquitin levels showed a positive significant correlation in both species, suggesting that their association is important in thermal tolerance. Histopathological observations of muscle tissue in P. serratus showed no gross alterations due to temperature but did show localized atrophy of muscle fibers at CTMax. In P. elegans, alterations occurred at a larger scale, showing multiple foci of atrophic muscular fascicles caused by necrotic or autolytic processes. In conclusion, Palaemon congeners displayed different responses to stress at a cellular level, with P. elegans having greater biomarker levels and histopathological alterations.

Isopods failed to acclimate their thermal sensitivity of locomotor performance during predictable or stochastic cooling

Most organisms experience environments that vary continuously over time, yet researchers generally study phenotypic responses to abrupt and sustained changes in environmental conditions. Gradual environmental changes, whether predictable or stochastic, might affect organisms differently than do abrupt changes. To explore this possibility, we exposed terrestrial isopods (Porcellio scaber) collected from a highly seasonal environment to four thermal treatments: (1) a constant 20°C; (2) a constant 10°C; (3) a steady decline from 20° to 10°C; and (4) a stochastic decline from 20° to 10°C that mimicked natural conditions during autumn. After 45 days, we measured thermal sensitivities of running speed and thermal tolerances (critical thermal maximum and chill-coma recovery time). Contrary to our expectation, thermal treatments did not affect the thermal sensitivity of locomotion; isopods from all treatments ran fastest at 33° to 34°C and achieved more than 80% of their maximal speed over a range of 10° to 11°C. Isopods exposed to a stochastic decline in temperature tolerated cold the best, and isopods exposed to a constant temperature of 20°C tolerated cold the worst. No significant variation in heat tolerance was observed among groups. Therefore, thermal sensitivity and heat tolerance failed to acclimate to any type of thermal change, whereas cold tolerance acclimated more during stochastic change than it did during abrupt change.

Zebrafish take their cue from temperature but not photoperiod for the seasonal plasticity of thermal performance

Organisms adjust to seasonal variability in the environment by responding to cues that indicate environmental change. As most studies of seasonal phenotypic plasticity test only the effect of a single environmental cue, how animals may integrate information from multiple cues to fine-tune plastic responses remains largely unknown. We examined the interaction between correlated (seasonally matching) and conflicting (seasonally opposite) temperature and photoperiod cues on the acclimation of performance traits in male zebrafish, Danio rerio. We acclimated fish for 8 weeks and then tested the change in thermal dependence of maximum burst swimming and feeding rate between 8 and 38°C. We predicted that correlated environmental cues should induce a greater acclimation response than uncorrelated cues. However, we found that only temperature was important for the seasonal acclimation of performance traits in zebrafish. Thermal acclimation shifted the thermal performance curve of both traits. For maximum burst swimming, performance increased for each group near the acclimation temperature and reduced in environments that were far from their acclimation temperature. The feeding rate of cold-acclimated zebrafish was reduced across the test temperature range compared with that of warm-acclimated fish. Our study is the first that has found no effect of the covariation between temperature and photoperiod acclimation cues on locomotor performance in fishes. Our results support the intuitive idea that photoperiod may be a less important seasonal cue for animals living at lower latitudes.

Effects of temperature, salinity, body length, and starvation on the critical swimming speed of whiteleg shrimp, Litopenaeus vannamei

The critical swimming speed (U(crit), cms⁻¹) of whiteleg shrimp, Litopenaeus vannamei, exposed to various temperatures (17, 20, 25, and 29 °C), salinities (20, 25, 30, 35, and 40), and starvation days (1, 4, and 8d), was determined in a flume tank. Body length (5.5, 6.6, 7.3, 9.4, and 10.0 cm) was also studied in relation to the U(crit). Temperature, salinity, body length and starvation significantly affected the U(crit) of whiteleg shrimp. The U(crit) increased as temperature increased from 17 to 29 °C. The relationship between temperature (t, °C) and U(crit) can be described by the linear model as U(crit)=1.5916t+0.8892, R²=0.9992 (P<0.01). The U(crit) increased and then decreased as salinity increased from 20 to 40. The optimum salinity and the corresponding maximum U(crit) are 36.17 and 42.87 cms⁻¹, respectively. The relationship between salinity (s) and U(crit) can be described by the quadratic model as U(crit)=-0.0171s²+1.2371s+20.497, R²=0.7667 (P=0.234). The U(crit) increased as body length increased from 5.5 to 10.0 cm, whereas relative critical swimming speed (U(crit)', BLs⁻¹) decreased. The relationship between body length (l, cm) and U(crit) or U(crit)' can be described by the quadratic model as U(crit)=-0.6233l²+12.302l-20.264, R²=0.9942 (P<0.01) or U(crit)'=-0.0514l²+0.5351l+3.8132, R²=0.9862 (P<0.05). The U(crit) decreased as starvation days increased from 1 to 8d. The relationship between starvation day (d, d) and U(crit) can be described by the quadratic model as U(crit)=-0.1262d²-0.0395d +40.979, R²=1. Low temperatures and salinity and starvation can reduce the swimming speed of whiteleg shrimp. Results can be of value in evaluating the locomotive ability, understanding ecological processes, and improving the capture and stock enhancement of whiteleg shrimp.

The effects of acute temperature change on cost of transport at maximal labriform speed in bluegill Lepomis macrochirus

The effects of acute temperature change on the cost of bluegill Lepomis macrochirus swimming were quantified. At 14 degrees C, maximum labriform swimming speed (U(lab,max)) was reduced relative to that at the acclimation temperature of 22 degrees C, but total cost of transport (T(TC)) remained unchanged. At 30 degrees C, U(lab,max) was the same as at 22 degrees C, but T(TC) was 66% greater.

Effect of temperature on swimming performance in juvenile southern catfish (Silurus meridionalis)

The critical swimming speed (U(crit), aerobic swimming performance) and endurance (anaerobic swimming performance) of juvenile southern catfish Silurus meridionalis Chen (9.8+/-0.1 cm body length and 8.09+/-0.17 g body mass, n=226) were investigated at 10, 15, 20, 25, and 30 degrees C. Both absolute U(crit) (cm s(-1)) and relative critical swimming speed (U(r), BL s(-1)) of juvenile southern catfish increased in the temperature zone from 10 to 25 degrees C (p<0.05) and plateaued between 25 and 30 degrees C. However, the relationship between endurance time (tested at 1.23, 1.59 and 1.79 U(r-max)) and temperature followed an approximate bell-shape curve as temperature rose (p<0.05). The optimum temperatures of maximal U(crit) (3.40 BL s(-1)) of juvenile southern catfish was 28.4 degrees C. But that of experimental fish's endurance which was tested at velocity of 1.59 and 1.79 U(r-max) was 23.2 degrees C. These results show that temperature has a significant effect on swimming performance in juvenile southern catfish.

Complex physiological traits as biomarkers of the sub-lethal toxicological effects of pollutant exposure in fishes

Complex physiological traits, such as routine aerobic metabolic rate or exercise performance, are indicators of the functional integrity of fish that can reveal sub-lethal toxicological effects of aquatic pollutants. These traits have proved valuable in laboratory investigations of the sub-lethal effects of heavy metals, ammonia and various xenobiotics. It is not known, however, whether they can also function as biomarkers of the complex potential range of effects upon overall functional integrity caused by exposure to mixtures of chemicals in polluted natural environments. The current study used portable swimming respirometers to compare exercise performance and respiratory metabolism of fish exposed in cages for three weeks to either clean or polluted sites on three urban European river systems: the river Lambro, Milan, Italy; the rivers Blythe, Cole and Tame, Birmingham, UK; and the river Amstel, Amsterdam, The Netherlands. The UK and Italian rivers were variously polluted with high levels of both bioavailable heavy metals and organics, and the Amstel by mixtures of bioavailable organics at high concentrations. In both the UK and Italy, indigenous chub (Leuciscus cephalus) exposed to clean or polluted sites swam equally well in an initial performance test, but the chub from polluted sites could not repeat this performance after a brief recovery interval. These animals were unable to raise the metabolic rate and allocate oxygen towards exercise in the second trial, an effect confirmed in successive campaigns in Italy. Swimming performance was therefore a biomarker indicator of pollutant exposure in chub exposed at these sites. Exposure to polluted sites on the river Amstel did not affect the repeat swimming performance of cultured cloned carp (Cyprinus carpio), indicating either a species-specific tolerance or relative absence of heavy metals. However, measurements of oxygen uptake during swimming revealed increased rates of routine aerobic metabolism in both chub and carp at polluted sites in all of the rivers studied, indicating a sub-lethal metabolic loading effect. Therefore, the physiological traits of exercise performance and metabolic rate have potential as biomarkers of the overall sub-lethal toxic effects of exposure to complex mixtures of pollutants in rivers, and may also provide insight into why fish do not colonize some polluted environments.

Swimming performance and energetics as a function of temperature in killifish Fundulus heteroclitus

Populations of the common killifish Fundulus heteroclitus are found along a latitudinal temperature gradient in habitats with high thermal variability. The objectives of this study were to assess the effects of temperature and population of origin on killifish swimming performance (assessed as critical swimming speed, U(crit)). Acclimated fish from northern and southern killifish populations demonstrated a wide zone (from 7 degrees to 33 degrees C) over which U(crit) showed little change with temperature, with performance declining significantly only at lower temperatures. Although we observed significant differences in swimming performance between a northern and a southern population of killifish in one experiment, with northern fish having an approximately 1.5-fold-greater U(crit) than southern fish across all acclimation temperatures, we were unable to replicate this finding in other populations or collection years, and performance was consistently high across all populations and at both low (7 degrees C) and high (23 degrees C) acclimation temperatures. The poor swimming performance of southern killifish from a single collection year was correlated with low muscle [glycogen] rather than with other indicators of fuel stores or body condition. Killifish acclimated to 18 degrees C and acutely challenged at temperatures of 5 degrees , 18 degrees , 25 degrees , or 34 degrees C showed modest thermal sensitivity of U(crit) between 18 degrees and 34 degrees C, with performance declining substantially at 5 degrees C. Thus, much of the zone of relative thermal insensitivity of swimming performance is intrinsic in this species rather than acquired as a result of acclimation. These data suggest that killifish are broadly tolerant of changing temperatures, whether acute or chronic, and demonstrate little evidence of local adaptation in endurance swimming performance in populations from different thermal habitats.

Effects of temperature, swimming speed and body mass on standard and active metabolic rate in vendace (Coregonus albula)

This study gives an integrated analysis of the effects of temperature, swimming speed and body mass on standard metabolism and aerobic swimming performance in vendace (Coregonus albula (L.)). The metabolic rate was investigated at 4, 8 and 15 degrees C using one flow-through respirometer and two intermittent-flow swim tunnels. We found that the standard metabolic rate (SMR), which increased significantly with temperature, accounted for up to 2/3 of the total swimming costs at optimum speed (U (opt)), although mean U (opt) was high, ranging from 2.0 to 2.8 body lengths per second. Net swimming costs increased with swimming speed, but showed no clear trend with temperature. The influence of body mass on the metabolic rate varied with temperature and activity level resulting in scaling exponents (b) of 0.71-0.94. A multivariate regression analysis was performed to integrate the effects of temperature, speed and mass (AMR = 0.82M (0.93) exp(0.07T) + 0.43M (0.93) U (2.03)). The regression analysis showed that temperature affects standard but not net active metabolic costs in this species. Further, we conclude that a low speed exponent, high optimum speeds and high ratios of standard to activity costs suggest a remarkably efficient swimming performance in vendace.

Effect of temperature on maximum swimming speed and cost of transport in juvenile European sea bass (Dicentrarchus labrax)

This study is an attempt to gain an integrated understanding of the interactions between temperature, locomotion activity and metabolism in the European sea bass (Dicentrarchus labrax). To our knowledge this study is among the few that have investigated the influence of the seasonal changes in water temperature on swimming performance in fish. Using a Brett-type swim-tunnel respirometer the relationship between oxygen consumption and swimming speed was determined in fish acclimatised to 7, 11, 14, 18, 22, 26 and 30 degrees C. The corresponding maximum swimming speed (U(max)), optimal swimming speed (U(opt)), active (AMR) and standard (SMR) metabolic rates as well as aerobic metabolic scope (MS) were calculated. Using simple mathematical functions, these parameters were modelled as a function of water temperature and swimming speed. Both SMR and AMR were positively related to water temperature up to 24 degrees C. Above 24 degrees C SMR and AMR levelled off and MS tended to decrease. We found a tight relationship between AMR and U(max) and observed that raising the temperature increased AMR and increased swimming ability. However, although fish swam faster at high temperature, the net cost of transport (COT(net)) at a given speed was not influence by the elevation of the water temperature. Although U(opt) doubled between 7 degrees C and 30 degrees C (from 0.3 to 0.6 m s(-1)), metabolic rate at U(opt) represented a relatively constant fraction of the animal active metabolic rate (40-45%). A proposed model integrates the effects of water temperature on the interaction between metabolism and swimming performance. In particular the controlling effect of temperature on AMR is shown to be the key factor limiting maximal swimming speed of sea bass.

Temperature- and exercise-induced gene expression and metabolic enzyme changes in skeletal muscle of adult zebrafish (Danio rerio)

Both exercise training and cold acclimatization induce muscle remodelling in vertebrates, producing a more aerobic phenotype. In ectothermic species exercise training and cold-acclimatization represent distinct stimuli. It is currently unclear if these stimuli act through a common mechanism or if different mechanisms lead to a common phenotype. The goal of this study was to survey responses that represent potential mechanisms responsible for contraction- and temperature-induced muscle remodelling, using an ectothermic vertebrate. Separate groups of adult zebrafish (Danio rerio) were either swim trained or cold acclimatized for 4 weeks. We found that the mitochondrial marker enzyme citrate synthase (CS) was increased by 1.5x in cold and by 1.3x with exercise (P<0.05). Cytochrome c oxidase (COx) was increased by 1.2x following exercise training (P<0.05) and 1.2x (P=0.07) with cold acclimatization. However, only cold acclimatization increased beta-hydroxyacyl-CoA dehydrogenase (HOAD) compared to exercise-trained (by 1.3x) and pyruvate kinase (PK) relative to control zebrafish. We assessed the whole-animal performance outcomes of these treatments. Maximum absolute sustained swimming speed (Ucrit) was increased in the exercise trained group but not in the cold acclimatized group. Real-time PCR analysis indicated that increases in CS are primarily transcriptionally regulated with exercise but not with cold treatments. Both treatments showed increases in nuclear respiratory factor (NRF)-1 mRNA which was increased by 2.3x in cold-acclimatized and 4x in exercise-trained zebrafish above controls. In contrast, peroxisome proliferator-activated receptor (PPAR)-alpha mRNA levels were decreased in both experimental groups while PPAR-beta1 declined in exercise training only. Moreover, PPAR-gamma coactivator (PGC)-1alpha mRNA was not changed by either treatment. In zebrafish, both temperature and exercise produce a more aerobic phenotype, but there are stimulus-dependent responses (i.e. HOAD and PK activities). While similar changes in NRF-1 mRNA suggest that common responses might underlie aerobic muscle remodelling there are distinct changes (i.e. CS and PPAR-beta1 mRNA) that contribute to specific temperature- and exercise-induced phenotypes.