The thermal dependence of fast-start performance in fish

Many fish species use fast-starts to escape predators and capture prey. There is evidence for changes in fast-start behaviour with temperature, over acute, seasonal, developmental and evolutionary time scales. Maximum velocity often increases with acute temperature changes. Thermal acclimation can improve fast-start performance, although responses appear to be reduced in more eurythermal species. Changes in performance with thermal acclimation are often reflected at the molecular, biochemical and cellular levels of organisation. There appears to be little compensation in fast-start performance in Antarctic fish compared to warmer water species.     

Thermal sensitivity does not determine acclimation capacity for a tropical reef fish

1. Short-term measures of metabolic responses to warmer environments are expected to indicate the sensitivity of species to regional warming. However, given time, species may be able to acclimate to increasing temperature. Thus, it is useful to determine if short-term responses provide a good predictor for long-term acclimation ability. 2. The tropical reef fish Acanthochromis polyacanthus was used to test whether the ability for developmental thermal acclimation of two populations was indicated by their short-term metabolic response to temperature. 3. While both populations exhibited similar short-term responses of resting metabolic rate (RMR) to temperature, fish from the higher-latitude population were able to fully acclimate RMR, while the lower-latitude population could only partially compensate RMR at the warmest temperature. These differences in acclimation ability are most likely due to genetic differences between the populations rather than differences in thermal regimes. 4. This research indicates that acclimation ability may vary greatly between populations and that understanding such variation will be critical for predicting the impacts of warming environmental temperatures. Moreover, the thermal metabolic reaction norm does not appear to be a good predictor of long-term acclimation ability.     

Temperature mediated processes in teleost immunity: differential abilities of channel catfish T and B lymphocytes to cap membrane antigen

1. The effect of both in vivo acclimation temperature and in vitro assay temperatures on channel catfish T and B lymphocyte membrane antigen (mAg) capping were investigated to determine if capping might be the temperature sensitive step involved in the low temperature immunosuppression of channel catfish T cell responses. 2. Flow cytometry was used to monitor the kinetics of capping induced by a mouse monoclonal antibody (mAb 11G3) specific for a common antigenic determinant present on channel catfish T and B cells. Results indicated that the kinetics of mAg capping were dependent on in vitro assay and in vivo acclimation temperatures and the length of time of in vivo acclimation. 3. T cells from fish appropriately acclimated to 27 degrees C cap mAg more efficiently at low assay temperatures than do B cells. 4. Activation energies were 32 and 47 kcal/mol for B and T cells, respectively, from fish acclimated to 17 degrees C for 3 weeks, but were significantly lower (14 and 22 kcal/mol, respectively) after acclimation for 5 weeks. 5. In summary, it appears that after appropriate in vivo acclimation, channel catfish T cells are better able to cap mAg at low assay temperatures than are B cells. These results suggest that mAg capping is not the low temperature sensitive step involved in T cell immunosuppression in channel catfish.     

温度驯化对尖头鳉热耐受特征的影响

为了研究不同驯化温度对尖头鰂(Rhynchocypris oxycephalus)热耐受特征的影响, 本研究设置4组水温(14℃、19℃、24℃和29℃), 对尖头鰂驯化两周, 采用临界温度法观察尖头鰂的耐受温度。结果显示: 尖头鰂的热耐受性受到温度驯化的影响, 表现为高温驯化可以升高最大临界温度(CT_max), 4个驯化组的平均CT_max分别为32.29℃、33.23℃、33.40℃和35.71℃; 低温驯化可以降低最小临界温度(CT_min), 平均CT_min分别为0.00、0.10℃、2.10℃和5.27℃; 在适中的温度(19℃)驯化条件下具有最高的温度耐受范围(33.13℃)。在高温条件下的温度驯化具有较高的驯化反应率, 最大值出现在24—29℃内(0.46); 低温驯化反应率最大值出现在29—24℃内, 为0.63。尖头鰂在本研究的驯化区间(14—29℃)内的热耐受区域面积为478.98℃2, 与温水性鱼类的温度耐受性相当, 说明尖头鰂具有较强的温度适应能力。     

Temperature selection and avoidance in the sand goby,Pomatoschistus minutus (Pallas), collected at different seasons

Synopsis The sand goby from the Oslofjord, Norway, is extremely eurythermal. In spring and autumn it avoids temperatures lower than about 4° C, in summer 6° C. Acclimation did not influence the lower avoidance temperature, but the critical thermal maximum, the upper avoidance temperature and the temperature where the whole fish darkened (the darkening temperature) varied with acclimation and season. The darkening temperature is suggested to be the upper temperature limit with the greatest ecological significance. The fish, collected at different seasons darkened at between 19.5 and 22° C. In the field the fish is not found at 20° C and higher.The preference temperature varied with season and with acclimation temperature, generally with low precision. In May, the preference temperature was 13.5° C, that is higher than the ambient temperature of 10° C. In summer, the temperature in sampling locality and preference temperature was the same, 17 and 16.5° C respectively. In October, temperature preference was 7.5° C as compared to 9° C in the field. The variation is explained as a behavioural thermoregulation to direct the fish towards optimal conditions at any time.The seasonal variation in preference temperature can not be ascribed only to seasonal variation in temperature, that is an acclimation phenomenon, but other factors are operative as well, factors which will modify the temperature tolerance in the fish.     

Dynamic Phosphoproteome Profiling of Zebrafish Embryonic Fibroblasts during Cold Acclimation

Temperature affects almost all aspects of the fish life. To cope with low temperature, fish have evolved the ability of cold acclimation for survival. However, intracellular signaling events underlying cold acclimation in fish remain largely unknown. Here, the formation of cold acclimation in zebrafish embryonic fibroblasts (ZF4) is monitored and the phosphorylation events during the process are investigated through a large‐scale quantitative phosphoproteomic approach. In total, 11 474 phosphorylation sites are identified on 4066 proteins and quantified 5772 phosphosites on 2519 proteins. Serine, threonine, and tyrosine (Ser/Thr/Tyr) phosphorylation accounted for 85.5%, 13.3%, and 1.2% of total phosphosites, respectively. Among all phosphosites, 702 phosphosites on 510 proteins show differential regulation during cold acclimation of ZF4 cells. These phosphosites are divided into six clusters according to their dynamic changes during cold exposure. Kinase–substrate prediction reveals that mitogen‐activated protein kinase (MAPK) among the kinase groups is predominantly responsible for phosphorylation of these phosphosites. The differentially regulated phosphoproteins are functionally associated with various cellular processes such as regulation of actin cytoskeleton and MAPK signaling pathway. These data enrich the database of protein phosphorylation sites in zebrafish and provide key clues for the elucidation of intracellular signaling networks during cold acclimation of fish.     

TEMPERATURE ACCLIMATION AND THE NERVOUS SYSTEM

1. The conduction velocity of the compound action potential of peripheral nerves shows compensatory acclimation to temperature in a fish, a snail, a crab, and probably also in the frog. The heat and cold tolerances of peripheral conduction are probably both increased by cold acclimation in the frog. 2. The properties of compound action potentials are not suitable for temperature acclimation studies, since different neuronal populations in the same nerve have been found to exhibit different temperature characteristics. 3. Single but septate giant nerve fibres of earthworms show compensatory temperature acclimation of the conduction properties, the form of the action potential and of the axonal cable properties, especially below 13–19 °C. 4. The fatty acids and the plasmalogen aldehydes of the phospholipids of the goldfish brain are more unsaturated at lower acclimation temperatures. 5. The Na⁺-K⁺ ATPase activity of the earthworm nerve cord shows compensatory acclimation at low temperatures. 6. The spontaneous activity of the central nervous system of insects is altered in a compensatory manner by temperature acclimation. In fish, the cold tolerance of simple and complex reflexes and of conditioning is adaptively altered by temperature acclimation. The role of the central nervous system, especially of the thermoregulatory centre, in the temperature acclimation of homeotherms is established. 7. There are adaptive isoenzymes of acetylcholinesterase in the brain of the rainbow trout. These isoenzymes differ from each other in respect of the temperature dependence of their enzyme-substrate affinity. The synthesis of acetylcholine receptor molecules may also be affected by temperature acclimation. 8. The metabolism of putative synaptic neurotransmitters (5-hydroxytryptamine, adrenaline, noradrenaline) is altered in the frog and mouse brains during the early phases of temperature acclimation. These changes may initiate the physiological processes connected with temperature acclimation. 9. The neuromuscular transmission in the frog shows after acclimation to cold, increased resistance to it and some indications of temperature compensation. 10. Changes in neurosecretion seem to be involved in temperature acclimation both in poikilotherms and homeotherms. The fast axonal transport of proteins shows compensatory acclimation to cold in the frog.     

The effect of thermal acclimation on the activity of arylhydrocarbon hydroxylase in rainbow trout (Oncorhynchus mykiss)

1. The possibility that temperature acclimation (to 10 or 18 degrees C for 28 days) would alter the cytochromes P-450 of rainbow trout was addressed. 2. The specific content of LM4b (P-450 IA1), the trout isozyme responsible for activation of polynuclear aromatic hydrocarbons, was lower in 18 degrees C fish than it was in 10 degrees C fish. 3. Kinetic analysis of aryl hydrocarbon hydroxylase indicated that, while thermal acclimation caused no change in Vmax, it lowered the apparent Km of this enzyme for benzo[a]pyrene when assayed at acutely shifted temperatures. 4. Thermal acclimation of fish may have significance when feral populations are subjected to acute temperature shifts.     

Acclimation to temperature and death at changing lethal temperatures in the freshwater fish Chalcalburnues chalcoides

1. 1.|In the freshwater fish Chalcalburnus chalcoides, an increase in the body (standard) size caused decreases in the upper LT-50 from 36.6° to 36.0°C and lower LT-50 from 6.3° to 5.3°C

2. 2.|The fish acclimated to constant temperatures between 10°C and 30°C showed reasonable heat acclimation and also reasonable cold acclimation. Thus, an increase in the acclimation temperature from 10°C to 30°C caused increases in the upper LT-50 from 34° to 36.2°C and the lower LT-50 from 1.25 to 6.5°C.

3. 3|The mean survival time — temperature curves of 10°, 20° and 30°C acclimated fish at various constant temperatures showed decreased in the survival tim ewith increasing lethal temperatures. Furthermore, an increase in the acclimation temperature causes a shift in the survival duration-temperature curve to the right, i.e., the fish become more heat resistant. Thus, the mean survival duration of 10°, 20° and 30°C acclimated fish at 35°C were 7.5, 79.6 and 530 minutes, respectively.

4. 4.|The effect of the thermal experience to changing lethal temperatures depends on the first lethal temperature to which the fish were exposed as well as the sequence of temperature changes. In the experiments in which the first lethal temperatures were between 32° and 34°C and the temperature was varied in an ascending order, their thermal resistance was increased and the fish required 114 to 174% of the expected lethal doses to die while in the experiments in which the starting temperature were between 38° and 40°C and the temperature varied in descending order, the fish become more sensitive to the upper lethal temperature and they died after receiving only 62 to 81% of the expected lethal doses. Thus, with a gradual increase in the lethal temperature, the fish show additional acclimation in the zone of resistance which in turn causes an increase in the thermal resistance. This may have ecological significance in nature.

Thermal acclimation is not necessary to maintain a wide thermal breadth of aerobic scope in the common killifish (Fundulus heteroclitus)

Loss of aerobic scope at high and low temperatures is a physiological mechanism proposed to limit the thermal performance and tolerance of organisms, a theory known as oxygen- and capacity-limited thermal tolerance (OCLTT). Eurythermal organisms maintain aerobic scope over wide ranges of temperatures, but it is unknown whether acclimation is necessary to maintain this breadth. The objective of this study was to examine changes in aerobic scope in Fundulus heteroclitus, a eurythermal fish, after acclimation and acute exposure to temperatures from 5° to 33°C. The range of temperatures over which aerobic scope was nonzero was similar in acclimated and acutely exposed fish, suggesting that acclimation has modest effects on the thermal breadth of aerobic scope. However, in acclimated fish, there was a clear optimum temperature range for aerobic scope between 25° and 30°C, whereas aerobic scope was relatively constant across the entire temperature range with acute temperature exposure. Therefore, the primary effect of acclimation was to increase aerobic scope between 25° and 30°C, which paradoxically resulted in a narrower temperature range of optimal performance in acclimated fish compared to acutely exposed fish. There was only weak evidence for correlations between the thermal optimum of aerobic scope and the thermal optimum of measures of performance (specific growth rate and gonadosomatic index), and indicators of anaerobic metabolism (lactate accumulation and lactate dehydrogenase activity) only increased at high temperatures. Together these data fit many, but not all, of the predictions made by OCLTT.     

Effect of temperature on osmotic and ionic regulation in goldfish,Carassius auratus L.

Summary Urine flow increased with acute temperature increases and showed temperature acclimation. When measured at 20 °C the urine flow of 10 °C acclimated fish was 3.2 times greater than the urine flow of 30 °C acclimated fish. In fish acclimated to 24 °C renal reabsorption of Na and Cl was independent of temperature over an intermediate range of temperatures (14–24 °C) but near the lower lethal temperature (6.5 °C) renal Na and Cl reabsorption was inhibited. Water permeability of the renal tubules was not affected by acute temperature change between 6.5 and 24 °C. Urine osmolality and urine Na, K and Cl concentrations showed nearly perfect temperature compensation in fish acclimated to 10 °C and 30 °C. The rate of renal excretion of Na and Cl showed temperature acclimation in that Na and Cl ecxretion measured at 20 °C was 7 to 8 times greater in 10 °C acclimated fish than in 30 °C acclimated fish. The rate of excretion of Na and Cl measured at 30 °C in 30 °C acclimated fish was approximately 1.7 times the rate of excretion measured at 10 °C in 10 °C acclimated fish.The branchial uptake of Na, measured in tap water, of fish acclimated to 10, 20 and 30 °C in demineralized water increased with acute increases in temperature. When the three acclimation groups were compared at an intermediate temperature (20 °C), the 10 °C acclimated group showed the highest rate of net uptake, and the 30 °C group the lowest rate of uptake. This apparent temperature acclimation of Na uptake was correlated with differences in the plasma Na concentration of the three acclimation groups. Plasma Cl concentrations were also correlated with acclimation temperature in fish acclimated in demineralized water, but the rate of net Cl uptake was considerably less than that for Na. Sodium and Cl uptake in fish which had been acclimated in tap water was very variable and was not clearly affected by acute changes in temperature. Uptake of Na and Cl by fish held in tap water did not show temperature acclimation. The difference between uptake and excretion of fish acclimated in tap water was not significantly different from zero, indicating that the fish were in salt balance.The study was supported by National Institutes of Health Grant GM 16932-02 to Dr. Bodil Schmidt-Nielsen. I am grateful to Dr. Schmidt-Nielsen for many useful discussions during the course of this work.     

Reproductive Acclimation to Increased Water Temperature in a Tropical Reef Fish

Understanding the capacity of organisms to cope with projected global warming through acclimation and adaptation is critical to predicting their likely future persistence. While recent research has shown that developmental acclimation of metabolic attributes to ocean warming is possible, our understanding of the plasticity of key fitness-associated traits, such as reproductive performance, is lacking. We show that while the reproductive ability of a tropical reef fish is highly sensitive to increases in water temperature, reproductive capacity at +1.5°C above present-day was improved to match fish maintained at present-day temperatures when fish complete their development at the higher temperature. However, reproductive acclimation was not observed in fish reared at +3.0°C warmer than present-day, suggesting limitations to the acclimation possible within one generation. Surprisingly, the improvements seen in reproduction were not predicted by the oxygen- and capacity-limited thermal tolerance hypothesis. Specifically, pairs reared at +1.5°C, which showed the greatest capacity for reproductive acclimation, exhibited no acclimation of metabolic attributes. Conversely, pairs reared at +3.0°C, which exhibited acclimation in resting metabolic rate, demonstrated little capacity for reproductive acclimation. Our study suggests that understanding the acclimation capacity of reproductive performance will be critically important to predicting the impacts of climate change on biological systems.     

Heat Resistance and Thermal Acclimation Rate in Tropical Tetra <Emphasis Type="Italic">Astyanax bimaculatus</Emphasis> of Venezuela

Venezuelan river tetra, Astyanax bimaculatus juveniles of 34.1–36.7mm standard length and 0.83–1.0g wet weight were acclimated for four weeks to 24–33°C, which are approximate average minimum and maximum river temperatures throughout the year. The fish acclimated to 24, 27, 30, and 33°C were exposed for 10000 minutes at 35, 36, 37, 38, and 39°C to determine individual heat resistance times. To determine acclimation rates, the juveniles acclimated to 24 and 30°C were tested for individual heat resistance times at 39°C by changing acclimation temperatures. The individual heat resistance times were increased in accordance with an increase in acclimation temperature and a decrease in test temperature, indicating that acclimation level has a great influence on thermal resistance of the fish tested. As the fish were transferred from 24 to 30°C (upward acclimation), they completed their acclimation level in a few days, while those transferred from 30 to 24°C (downward acclimation) required about 14 days. It has reaffirmed the following general behavior: the rate of gain in thermal resistance is fast and the loss in heat tolerance is very slow. This physiological phenomenon is very important for tropical fish, which acclimates rapidly in rising temperature during the hot day and does not lose this level in decreasing temperature during the cool night. Consequently, a tropical fish can maintain its maximum resistance level, adapt well in thermally fluctuating tropical waters, and survive in lethally high temperatures caused by a sudden increase in temperature during hot day.     

Quantification of the Role of Acclimation Temperature in Temperature Tolerance of Fishes

The relative effect of acclimation temperature on temperature tolerance was estimated from a geometrical partitioning of the temperature tolerance polygon of a fish species into three distinct zones relative to four key tolerance temperatures. This approach yields a middle tolerance zone which is independent of acclimation temperature bounded by upper and lower acclimation dependent zones. Acclimation dependent and independent temperature tolerance zones can be quantified by either areal or linear methods. Both methods were applied to quantify the effect of acclimation temperature in 21 species of temperate fishes for which temperature tolerance polygons were available. Temperature tolerance polygon areas of these 21 species ranged from 468 to 1380°C² and are linearly related (r ²=0.93, p<0.001) to ultimate incipient upper lethal temperatures. Although areal and linear partitioning methods yielded similar acclimation independent and dependent tolerances, estimates from the areal method incorporates additional information concerning the shape of the temperature tolerance polygon, in particular lower and upper lethal temperature plateaus. Mean combined acclimation dependent and independent tolerance areas of these 21 species were not different, indicating that acclimation effectively doubles the temperature tolerance polygon. Mean lower acclimation dependent area was nearly three times greater than mean upper acclimation dependent area, suggesting that acclimation plays a larger role in tolerance of low rather than high temperatures. Among these 21 species, temperature tolerance of brook charr and sheepshead minnow were the least and most affected by acclimation temperature, respectively.     

Effects of acclimation and incubation temperature on the glutathione antioxidant system in killifish and RTH-149 cells

Glutathione (GSH) is an important antioxidant that is involved in a multitude of cellular processes. However, in fish, GSH levels, turnover, and activity of associated enzymes are low when compared to those of mammals. To determine whether temperature influences the GSH antioxidant system in fish, and can explain the differences in GSH between fish and mammals, we examined the effects of acclimation temperature on total GSH (tGSH) levels and apparent half-life (as an estimate of turnover) in a rainbow trout hepatoma cell line (RTH-149), and GSH levels, and glutathione peroxidase (GPx) and reductase (GR) activity in the eurythermal killifish. Increasing incubation temperature decreased half-life and transiently increased levels of tGSH in RTH-149 cells. In killifish, increased acclimation temperature increased tGSH levels in the liver, brain and muscle, and increased hepatic GPx and GR activities. When the relationships between temperature and GSH half-life, levels and enzyme activity were extrapolated to 37 degrees C, temperature could only partially accounted for differences in the GSH antioxidant system in fish compared to mammals. The differences in the GSH antioxidant system between fish and mammals may not be solely due to temperature effects, but also to the increased metabolic cost of endothermy in mammals.     

Rate of acclimation of the tropical salt-marsh fish Cyprinodon dearborni to temperature changes

The acclimation rates of temperature changes in Cyprinodon dearborni, collected from Laguna Los Patos, Cumana, Venezuela, were determined by the critical thermal maximum method. At an increase in temperature (from 24 to 31°C) fish started to gain acclimation level after 3 hours and took 3 days to fully get up to a higher level of resistance to heat death; however, at a decrease in temperature (from 3 t to 24°C) fish began to lose its acclimation level after 12 days and required 39 days to reach a lower level of resistance to thermal death.     

Temperature-mediated processes in teleost immunity: the effects of temperature on membrane immunoglobulin capping on channel catfish B lymphocytes

1. In order to better understand ligand-induced redistribution of membrane receptors and lymphocyte activation in ectothermic vertebrates, flow cytometry was used to monitor the effects of both in vivo acclimation temperature and in vitro assay temperatures on the kinetics of monoclonal antibody-induced membrane immunoglobulin (mIg) capping on channel catfish lymphocytes. 2. It was observed that the kinetics of mIg capping were dependent on in vitro assay temperatures, in vivo acclimation temperatures, and the length of time of in vivo acclimation. In the latter situation in vivo acclimation of fish to 27, 22 and 17 degrees C was considered complete after 3 weeks, while acclimation to 12 degrees C required a minimum of 5 weeks. 3. The energies of activation required for mIg capping ranged from 33 to 24 kcal/mol; lower energies of activation were observed with lower temperature acclimation. 4. It was also noted that the lower energies of activation were associated with concomitant decreases in cellular phospholipid saturated/unsaturated fatty acid ratios. 5. It appears that channel catfish B cell mIg capping, presumably a requisite for immune function, can be significantly affected by environmental temperatures; most likely such effects are attributable to changes in plasma membrane viscosities.     

Tolerance and resistance to thermal stress in juvenile Atlantic salmon, Salmo salar

SUMMARY. 1. The chief objective was to construct a thermal tolerance polygon for juvenile Atlantic salmon, Salmo salar L., using fish from four groups and two populations: two age groups from one population (0+, 1+ parr from River Leven), two size groups from the other population (slow and Fast growing 1+ parr from River Lune). 2. Fish were acclimated to constant temperatures of 5, 10, 15, 20, 25 and 27°C; then the temperature was raised or lowered at 1°C h^?1 to determine the upper and lower limits for feeding and survival over 10 min, 100 min, 1000 min and 7 days. As they were not significantly different between the four groups of fish, values at each acclimation temperature were pooled to provide arithmetic means (with SE) for the thermal tolerance polygon. 3. Incipient lethal levels (survival over 7 days) defined a tolerance zone within which salmon lived for a considerable time; upper mean incipient values increased with increasing acclimation temperature to reach a maximum of 27.8±0.2°C, lower mean incipient values were below 0°C and were therefore undetermined at acclimation temperatures <20°C but increased at higher acclimation temperatures to 2.2±0.4°C. Resistance to thermal stress outside the tolerance zone was a function of time; the ultimate lethal level (survival for 10 min) increased with acclimation temperature to a maximum of 33°C whilst the minimum value remained close to 0°C. Temperature limits for feeding increased slightly with acclimation temperature to upper and lower mean values of 22.5±0.3°C and 7.0±0.3°C. 4. In spite of different methodologies, values in the present investigation are similar to those obtained in previous, less comprehensive studies in the laboratory. They also agree with field observations on the temperature limits for feeding and survival. Thermal tolerance polygons are now available for eight species of salmonids and show that the highest temperature limits for feeding and survival are those recorded for juvenile Atlantic salmon.     

Thermal acclimation effects differ between voluntary, maximum, and critical swimming velocities in two cyprinid fishes

Temperature acclimation may be a critical component of the locomotor physiology and ecology of ectothermic animals, particularly those living in eurythermal environments. Several studies of fish report striking acclimation of biochemical and kinetic properties in isolated muscle. However, the relatively few studies of whole-animal performance report variable acclimation responses. We test the hypothesis that different types of whole-animal locomotion will respond differently to temperature acclimation, probably due to divergent physiological bases of locomotion. We studied two cyprinid fishes, tinfoil barbs (Puntius schwanenfeldii) and river barbels (Barbus barbus). Study fish were acclimated to either cold or warm temperatures for at least 6 wk and then assayed at four test temperatures for three types of swimming performance. We measured voluntary swimming velocity to estimate routine locomotor behavior, maximum fast start velocity to estimate anaerobic capacity, and critical swimming velocity to estimate primarily aerobic capacity. All three performance measures showed some acute thermal dependence, generally a positive correlation between swimming speed and test temperature. However, each performance measure responded quite differently to acclimation. Critical speeds acclimated strongly, maximum speeds not at all, and voluntary speeds uniquely in each species. Thus we conclude that long-term temperature exposure can have very different consequences for different types of locomotion, consistent with our hypothesis. The data also address previous hypotheses that predict that polyploid and eurythermal fish will have greater acclimation abilities than other fish, due to increased genetic flexibility and ecological selection, respectively. Our results conflict with these predictions. River barbels are eurythermal polyploids and tinfoil barbs stenothermal diploids, yet voluntary swimming acclimated strongly in tinfoil barbs and minimally in river barbels, and acclimation was otherwise comparable.