The Relationship Among Swimming Performance, Courtship Behavior, and Carotenoid Pigmentation of Guppies in Four Rivers of Trinidad

In the laboratory, courtship behavior and carotenoid pigmentation of male guppies are condition-dependent traits, since their expression is affected by physical vigor and environmental factors such as water velocity and diet. Whether these relationships exist in guppies under field conditions is yet to be determined. We compared the swimming performance, courtship behavior, and carotenoid pigmentation of guppies from headwater and downstream localities in four rivers of Trinidad. Swimming performance and courtship behavior of males differed among rivers and between headwater and downstream sites. Guppies from headwater sites swam significantly faster and had higher display rates than those from downstream sites. Mean swimming performance across sites was positively correlated with mean water velocity, but was correlated with the number of orange color spots (carotenoid pigment) in only one river. These results indicate that the courtship behavior of Trinidadian guppies is condition-dependent because the amount of display behavior is positively correlated to swimming performance, a measure of physical endurance. The proximal cause for this condition-dependence may be predator induced variation in microhabitat use by guppies in headwater and downstream locations.     

Effects of capture and transmitter attachments on the swimming speed of large juvenile lemon sharks in the wild

The swimming speed of seven large juvenile lemon sharks Negaprion brevirostris following attachment of an external speed-sensing ultrasonic transmitter was significantly higher during the first 18 h after release compared to the average swimming speed obtained >48 h after release. The external speed-sensing transmitter can be used to monitor the voluntary swimming speed of large fishes in the field, but data during the first 24 h period should be excluded from analysis of natural speeds, at least from species similar in behaviour to N. brevirostris .     

Predation intensity does not cause microevolutionary change in maximum speed or aerobic capacity in trinidadian guppies (Poecilia reticulata Peters)

We measured maximal oxygen consumption (VO(2max)) and burst speed in populations of Trinidadian guppies (Poecilia reticulata) from contrasting high- and low-predation habitats but reared in "common garden" conditions. We tested two hypothesis: first, that predation, which causes rapid life-history evolution in guppies, also impacts locomotor physiology, and second, that trade-offs would occur between burst and aerobic performance. VO(2max) was higher than predicted from allometry, and resting VO(2) was lower than predicted. There were small interdrainage differences in male VO(2max), but predation did not affect VO(2max) in either sex. Maximum burst speed was correlated with size; absolute burst speed was higher in females, but size-adjusted speed was greater in males. For both sexes, burst speed conformed to allometric predictions. There were differences in burst speed between drainages in females, but predation regime did not affect burst speed in either sex. We did not find a significant correlation between burst speed and VO(2max), suggesting no trade-off between these traits. These results indicate that predation-mediated evolution of guppy life history does not produce concomitant evolution in aerobic capacity and maximum burst speed. However, other aspects of swimming performance (response latencies or acceleration) might show adaptive divergence in contrasting predation regimes.     

Shoaling in juvenile guppies: the effects of body size and shoal size

While factors affecting shoal mate choice have been examined extensively in adult guppies (Poecilia reticulata), few studies have focused on the shoaling behavior of juveniles. In this study, juvenile guppies were tested for their ability to shoal as well as their response to shoal mates of different body size and to shoals with different numbers of individuals. In dichotomous choice tests, 10-day-old guppies (mean body length=8.83 mm), 30-day-old guppies (13.17 mm) and 50-day-old guppies (18.6mm) were given the opportunity to swim near shoals of five fish or an empty chamber. In most cases, the juvenile fish demonstrated shoaling behavior, swimming near a group of fish rather than an empty chamber, regardless of the age of the stimulus shoal. When presented with two shoals, one of similar age and body size and one of dissimilar age and body size, only the 50-day-old guppies showed a significant preference for the age-matched shoal. Similarly, when choosing between a large shoal and a small shoal, only the 50-day-old guppies spent significantly more time near the larger shoal. Thus, while juveniles at each age shoaled, only 50-day-old fish demonstrated the shoal mate discrimination seen in adult fish.     

Estimation of fish activity costs using underwater video cameras

Swimming speed and activity costs of dace ( Phoxinus eos × P. neogaeus ) were estimated in the field using underwater video cameras. Activity costs were estimated by converting swimming speeds and the number of movements into swimming costs. Average swimming speed ranged from 6.7 to 12.2 cm.s⁻¹ across 2 h periods and varied significantly among dates and time of day. The time spent swimming by dace ranged from 616 to 17 640 s 2 h⁻¹. Activity costs per 2h period ranged from 2.1 to 4O.2J 2h⁻¹ and were strongly correlated to the time spent swimming. Daily activity cost estimated using the cameras averaged 128.9J day⁻¹ and was equivalent to 1.7 times the standard metabolic rate. Activity cost predicted using a bioenergetic model in conjunction with independent estimates of consumption and growth rates averaged 138.8J day⁻¹. This study indicated that swimming characteristics and activity costs of dace varied significantly both within and among days. These analyses also indicated that equally valid activity costs for fish in the field can be estimated using video cameras and the difference between Consumption and growth rates.     

Evaluating the time limit at maximum aerobic speed in elite swimmers. Training implications

The aim of the present study was to make use of the concepts of maximum aerobic speed (MAS) and time limit (tlim) in order to determine the relationship between these two elements, and this in an attempt to significantly improve both speed and swimming performance during a training season. To this same end, an intermittent training model was used, which was adapted to the value obtained for the time limit at maximum aerobic speed. During a 12 week training period, the maximum aerobic speed for a group of 9 top-ranking varsity swimmers was measured on two occasions, as was the tlim. The values generated indicated that: 1) there was an inverse relationship between MAS and the time this speed could be maintained, thus confirming the studies by Billat et al. (1994b); 2) a significant increase in MAS occurred over the 12 week period, although no such evolution was seen for the tlim; 3) there was an improvement in results; 4) the time limit could be used in designing a training program based on intermittent exercises. In addition, results of the present study should allow swimming coaches to draw up individualized training programs for a given swimmer by taking into consideration maximum aerobic speed, time limit and propelling efficiency.     

Maximum sustainable swimming speeds of late-stage larvae of nine species of reef fishes

We examined the maximum sustainable swimming speed of late-stage larvae of nine species of tropical reef fishes from around Lizard Island, Great Barrier Reef, Australia. Larvae were captured in light traps and were swum in flumes at different experimental swimming speeds (of 5 cm s⁻¹ intervals) continuously for 24 h. Logistic regression was used to determine the speed at which 90% of larvae were able to maintain swimming, and this was used to indicate the maximum sustainable swimming speed for each species. Maximum sustainable swimming speeds varied among the species examined, with the lethrinid maintaining the fastest sustainable swimming speed (24 cm s⁻¹), followed by the Pomacentridae (10-20 cm s⁻¹) and the Apogonidae (8-12 cm s⁻¹). U-crit (maximum speed) explained 64% of the variation in sustainable speed among species, whereas total length only explained 33% of the variation in sustained swimming. A regression fitted across species suggests that 50% U-crit is a good approximation of the speed able to be maintained by these larvae for 24 h. A model based on a cubic relationship between sustained swimming time and speed was found to be more successful than either length or U-crit as a method of estimating sustainable swimming speed for most of the species examined. Overall, we found that swimming speed is an important factor when considering the potential for active swimming behaviour to influence dispersal patterns, recruitment success and levels of self-recruitment in reef fish larvae and needs to be carefully considered in models of larval dispersal.     

The effect of submergence on heart rate and oxygen consumption of swimming seals and sea lions

Respiratory, metabolic, and cardiovascular responses to swimming were examined in two species of pinniped, the harbor seal (Phoca vitulina) and the California sea lion (Zalophus californianus). 1. Harbor seals remained submerged for 82-92% of the time at swimming speeds below 1.2 m.s-1. At higher speeds, including simulated speeds above 1.4 m.s-1, the percentage of time spent submerged decreased, and was inversely related to body weight. In contrast, the percentage of time spent submerged did not change with speed for sea lions swimming from 0.5 m.s-1 to 4.0 m.s-1. 2. During swimming, harbor seals showed a distinct breathhold bradycardia and ventilatory tachycardia that were independent of swimming speed. Average heart rate was 137 beats.min-1 when swimming on the water surface and 50 beats.min-1 when submerged. A bimodal pattern of heart rate also occurred in sea lions, but was not as pronounced as in the seals. 3. The weighted average heart rate (WAHR), calculated from measured heart rate and the percentage time spent on the water surface or submerged, increased linearly with swimming speed for both species. The graded increase in heart rate with exercise load is similar to the response observed for terrestrial mammals. 4. The rate of oxygen consumption increased exponentially with swimming speed in both seals and sea lions. The minimum cost of transport calculated from these rates ranged from 2.3 to 3.6 J.m-1.kg-1, and was 2.5-4.0 times the level predicted for similarly-sized salmonids. Despite different modes of propulsion and physiological responses to swimming, these pinnipeds demonstrate similar transport costs.     

Respiratory gas exchange,nitrogenous waste excretion,and fuel usage during aerobic swimming in juvenile rainbow trout

 The types of fuel burned by juvenile rainbow trout (17 g) during a 58-h period of aerobic sustained exercise were studied by respirometry. Attempts to measure fuel usage by depletion (the compositional approach) in these same fish were unsuccessful due to lack of detectable changes in proximate body composition. O₂ consumption, CO₂ excretion, and nitrogenous waste excretion (ammonia-N plus urea-N) were measured in individual fish swum continuously at 55% and 80% of maximum sustainable swimming speed and in non-swimming controls. O₂ consumption and CO₂ excretion increased with swimming speed, and decreased over time. Absolute rates of N excretion were independent of swimming speed and time. Instantaneous aerobic fuel use, as calculated from the respiratory quotients and nitrogen quotients, was approximately 47% lipid, 30% protein, and 23% carbohydrate in non-swimmers at the start of the experiment. With increased swimming speed there was no change in absolute rates of protein oxidation, while lipid and carbohydrate oxidation both increased. Therefore, the relative protein contribution decreased with increasing speed but increased with swimming duration as the oxidation of other fuels declined over time. However, lipid oxidation predominated at all speeds and at all times. The relative contribution of carbohydrate increased with swimming speed and decreased over time. These results suggest that swimming becomes more efficient over time and help resolve uncertainties in the literature. We conclude that lipid is the main fuel of aerobic exercise, that protein catabolism is kept at minimum levels necessary for maintenance, and that carbohydrate oxidation becomes more important with increased white muscle recruitment at higher speed. Accepted: 3 July 1996     

Courtship behavior,swimming performance,and microhabitat use of Trinidadian guppies

Synopsis We document differences in the use of microhabitats, male courtship behavior, and swimming performance of populations from headwater and downstream sites in two rivers of the Oropuche drainage in Trinidad. Guppies from headwater sites used microhabitats with higher water velocities, had a higher swimming performance, and were less patchily distributed than guppies from downstream sites. Although males from the headwater and downstream sites had similar display rates, males from headwater sites displayed in microhabitats with higher velocities (riffles) whereas males in downstream sites courted in still pools. Subtle effects of female choice maintain the honesty of male courtship behavior in various microhabitats. In downstream sites, where predators impose a survivorship cost on ornamental males, swimming performance was positively correlated with area of carotenoid ornamentation. In headwater sites, males frequently displayed in fast-flowing water, thus paid a higher metabolic cost of courtship. Interactions between characteristics of the physical habitat and predation pressure not only affect the distribution of guppies, but also have subtle effects on the types of condition-dependent traits favored by females.     

States of rest and activity in the Commerson's dolphin <Emphasis Type="Italic">Cephalorhynchus commersonii</Emphasis>

The unihemispheric slow-wave sleep, the ability to sleep during swimming with one open eye and the absence of paradoxical sleep in its form observed in all terrestrial mammals are unique features of sleep in cetaceans. Visual observation supplement electrophysiological studies and allow obtaining novel data about sleep of cetaceans. In the present study we examined behavior of 3 adult Commerson's dolphins Cephalorhynchus commersonii kept in the oceanarium Sea World (San Diego, CA, USA). The behavior of the dolphins can be subdivided into 5 swimming types: (1) active swimming marked by variable and irregular trajectory of movement (for 3 dolphins, on average, 35.1 ± 2.7% of the 24-h period) was the active wakefulness; (2) circular swimming was divided into the slow and fast swimming and occupied, on average, 44.4 ± 3.8 and 9.7 ± 0.8% of the 24-h period, respectively; during the circular swimming, dolphins performed from 1 to 6 circular swimming during one respiration pause; (3) quiet chaotic swimming (3.9 ± 1.2%) that occurred at the bottom and was not accompanied by signs of activity; (4) hanging, and (5) slow swimming at the surface (4.1 ± 0.5 and 2.8 ± 0.4%) respectively; the latter two swimming types were accompanied by frequent respiration (hyperventilation). We suggest that the sleep state in Commerson's dolphins occurs predominantly during the circular and quiet swimming. From time to time the dolphins decreased the speed, up to complete stop. Such episodes appeared to be the deepest sleep episodes. In all dolphins, muscle jerks as well erection in male are observed. Most jerks and erections occurred during the circular and quiet chaotic swimming. Thus, Commerson's dolphins, like other studied small cetaceans, are swimming for 24 h per day and they sleep during the swimming. Some muscle jerks that were observed in the dolphins in this study might have been brief episodes of paradoxical sleep.     

Cost of transport and optimal swimming speed in farmed and wild European silver eels (Anguilla anguilla)

A swimming speed of 0.4 meters per second (m s(-1)) is the minimal speed for European female silver eels to reach the spawning sites in the Sargasso Sea in time. As silver eels cease feeding when they start their oceanic migration, the cost of transport (COT) should be minimised and the swimming speed optimised to attain the highest energetic efficiency. In this study, we have investigated the optimal swimming speed (U(opt)) of silver eels since U(opt) may be higher than the minimal swimming speed and is more likely to resemble the actual cruise speed. A variety of swimming tests were performed to compare endurance swimming between farmed eels and wild eels, both in freshwater and in seawater. The swimming tests were run with 101 silver female eels (60-96 cm, 400-1500 g) in 22 Blazka-type swim tunnels in a climatised room at 18 degrees C with running freshwater or seawater. Tests were run at 0.5-1.0 m s(-1) with increments of 0.1 m s(-1), and either 2 h or 12 h intervals. Remarkably, both tests revealed no changes in oxygen consumption (M O2) and COT over time. U(opt) values ranged between 0.61 and 0.68 m s(-1) (0.74-1.02 BL s(-1)) for the different groups and were thus 53-70% higher than the minimal speed. At U(opt), the COT was 37-50 mg O2 kg(-1) km(-1). These relatively very low values confirm our earlier observations. COT values in seawater were about 20% higher than in freshwater. Assuming that migrating female silver eels cruise at their U(opt), they will be able to cover the distance to the Sargasso Sea in 3-4 months, leaving ample time for final maturation and finding mates.     

流速对细鳞裂腹鱼游泳行为及能量消耗影响的研究

通过自制密封的鱼类游泳实验装置, 研究了流速对细鳞裂腹鱼游泳行为和能量消耗的影响。结果显示,细鳞裂腹鱼的摆尾频率随游泳速度的变化有明显的变化规律, 摆尾频率随着流速的增加而显著性的增加,而摆尾幅度有减小趋势, 差异性不显著。结果还表明, (26±1) ℃时, (10.60±0.54) cm 细鳞裂腹鱼的相对临界游泳速度为(11.5±0.5) BL/s, 绝对临界游泳速度为(110.28±2.02) cm/s。测定的相对临界流速较其他的鲤科鱼大,是对生存水流环境(流速0.5—1.5m/s)适应性的表现。这一结果表明鱼类的游泳能力是能够训练的。运动代谢率与相对流速的关系为, AMR = 93.08e(0.307v) + 314.33, R2= 0.994; 单位距离能耗与流速的指数关系为COT =28e (-1.03V) +6.05, R2= 0.998。流速达到8 BL/s 时, 裂腹鱼耗氧率开始下降, 从流速7 BL/s 时, (1245.57±90.97 )mg O2/(kg·h)最大, 下降到(978.78±189.38) mg O2/(kg·h)。1—7 BL/s 流速范围内, 裂腹鱼单位时间内的耗氧率随着游泳速度的增加而增加, 而且随着游泳速度的增加, 单位距离能耗(COT)逐渐减少, 最小能耗在6 倍体长流速, 0.68 m/s 时, 为(6.00±1.57) J/(kg·m), 其能量利用效率最大。       

Swimming behaviour in Monoporeia affinis (Crustacea: Amphipoda) - dependence on temperature and population density

Swimming speed and swimming activity of the nocturnally active benthic amphipod Monoporeia affinis were measured in water temperatures from 3 to 18 degrees C and different population densities in the laboratory. Swimming speed increased with increasing temperature. Increasing water temperature reduced the percentage of active animals in the population, as measured by a "freeze frame" technique. At 7 and 10 degrees C a higher percentage of the population was active in higher animal densities. In all tested conditions swimming activity was highest at about 1 h after light-off and lowest shortly before the predicted time of light-on. The consequences of the documented behavioural responses to environmental stimuli are discussed in relation to population dynamics.     

Establishing zebrafish as a novel exercise model: swimming economy, swimming-enhanced growth and muscle growth marker gene expression

Background

Zebrafish has been largely accepted as a vertebrate multidisciplinary model but its usefulness as a model for exercise physiology has been hampered by the scarce knowledge on its swimming economy, optimal swimming speeds and cost of transport. Therefore, we have performed individual and group-wise swimming experiments to quantify swimming economy and to demonstrate the exercise effects on growth in adult zebrafish.

Methodology/Principal Findings

Individual zebrafish (n = 10) were able to swim at a critical swimming speed (U_crit) of 0.548±0.007 m s⁻¹ or 18.0 standard body lengths (BL) s⁻¹. The optimal swimming speed (U_opt) at which energetic efficiency is highest was 0.396±0.019 m s⁻¹ (13.0 BL s⁻¹) corresponding to 72.26±0.29% of U_crit. The cost of transport at optimal swimming speed (COT_opt) was 25.23±4.03 µmol g⁻¹ m⁻¹. A group-wise experiment was conducted with zebrafish (n = 83) swimming at U_opt for 6 h day⁻¹ for 5 days week⁻¹ for 4 weeks vs. zebrafish (n = 84) that rested during this period. Swimming zebrafish increased their total body length by 5.6% and body weight by 41.1% as compared to resting fish. For the first time, a highly significant exercise-induced growth is demonstrated in adult zebrafish. Expression analysis of a set of muscle growth marker genes revealed clear regulatory roles in relation to swimming-enhanced growth for genes such as growth hormone receptor b (ghrb), insulin-like growth factor 1 receptor a (igf1ra), troponin C (stnnc), slow myosin heavy chain 1 (smyhc1), troponin I2 (tnni2), myosin heavy polypeptide 2 (myhz2) and myostatin (mstnb).

Conclusions/Significance

From the results of our study we can conclude that zebrafish can be used as an exercise model for enhanced growth, with implications in basic, biomedical and applied sciences, such as aquaculture.     

Effects of feeding on medicinal leech swimming performance

The locomotor system of sanguivorous leeches is presented with a unique challenge: how to maintain mobility while coping with a >500% increase in body mass during feeding. A meal of this size is likely to disrupt the function of the muscular hydrostat during swimming, reducing speed and increasing predation risks. We quantified the effects of feeding to satiety on swimming kinematics, and the time course of recovery of swimming performance post-feeding in the medicinal leech Hirudo verbana . There was a 5.07 ± 0.04-fold increase in mass during feeding (mean ± sem , n =7). Despite this, leeches were able to swim immediately after feeding, reaching 27% of their pre-feeding speed. Reduced speed was a consequence of a reduction in both swimming cycle frequency and stride length to 69 and 42% of the pre-feeding values, respectively. Recovery of swimming ability was rapid, despite a prolonged increase in body mass. Fifty per cent restoration of swimming speed was achieved in c . 1 h while body mass was still 4.2-fold greater than before feeding. Rapid mass and volume reduction immediately post-feeding, and the properties of the obliquely striated swimming muscles appear to aid recovery of swimming performance. Such features that aid post-feeding recovery of mobility may have been important in the evolution of leech sanguivory.     

The influence of water velocity on the display behavior of male guppies, Poecilia reticulata

The objective of this experiment was to determine if differentwater velocities during ontogeny affect male physical condition,male signal intensity, and female mating preferences in theguppy (Poecilia reticulata). Guppies were raised in aquariain either high or low water velocities and fed in excess. Analysisof 72 males from four replicates indicated that high velocitymales had longer mean displays and spent more total time displayingthan low velocity males. These males also had significantlyfaster swimming speeds, wider caudal peduncles, and were moreattractive to females than low velocity males. There were nodifferences in display rates, body widths, standard lengths,or copulation attempts between high and low velocity males.These results indicate that water velocity conditions duringontogeny act as a proximal factor that influences the displaybehavior of guppies. Water velocity caused an indirect increasein the power of the male display to produce a female sexualresponse. The morpho-metric measurements suggest that the proximalmechanism behind the increased display intensity was the increasedmuscle development of males raised in high water velocities,which resulted in longer prolonged swimming speeds and moreintense displays. Therefore, display behavior of guppies maybe a general indicator of overall male physical condition.[BehavEcol07: 272–278 (1996)]     

KINEMATIC VARIABLES AND BLOOD ACID-BASE STATUS IN THE ANALYSIS OF COLLEGIATE SWIMMERS’ ANAEROBIC CAPACITY

Short duration repeated maximal efforts are often used in swimming training to improve lactate tolerance, which gives swimmers the ability to maintain a high work rate for a longer period of time. The aim of the study was to examine the kinematics of swimming and its relation to the changes in blood acid-base status and potassium level. Seven collegiate swimmers, with at least 6 years of training experience, volunteered to participate in the study. The test consisted of 8 x 25 m front crawl performed with maximum effort. The rest period between repetitions was set to five seconds. Blood samples were taken from the fingertip at rest, after warm-up and in the 3rd minute after completion of the test. The swimming was recorded with a video recorder, for later analysis of time, velocity and technique (stroke index). Based on the swimming velocity results, the obtained curve can be divided into rapid decrease of velocity and relatively stable velocities. The breaking point of repetition in swimming velocity was assumed as the swimming velocity threshold and it was highly correlated with the decrease of the blood acid-base status (pH r=0.82, BE r=0.87, HCO₃ ^- r=0.76; p<0.05 in all cases). There was no correlation between stroke index or fatigue index and blood acid-base status. Analysis of the swimming speed in the 8 x 25 m test seems to be helpful in evaluation of lactate tolerance (anaerobic capacity) in collegiate swimmers.     

Constraints on adaptive evolution: the functional trade-off between reproduction and fast-start swimming performance in the Trinidadian guppy (Poecilia reticulata)

The empirical study of natural selection reveals that adaptations often involve trade-offs between competing functions. Because natural selection acts on whole organisms rather than isolated traits, adaptive evolution may be constrained by the interaction between traits that are functionally integrated. Yet, few attempts have been made to characterize how and when such constraints are manifested or whether they limit the adaptive divergence of populations. Here we examine the consequences of adaptive life-history evolution on locomotor performance in the live-bearing guppy. In response to increased predation from piscivorous fish, Trinidadian guppies evolve an increased allocation of resources toward reproduction. These populations are also under strong selection for rapid fast-start swimming performance to evade predators. Because embryo development increases a female's wet mass as she approaches parturition, an increased investment in reproductive allocation should impede fast-start performance. We find evidence for adaptive but constrained evolution of fast-start swimming performance in laboratory trials conducted on second-generation lab-reared fish. Female guppies from high-predation localities attain a faster acceleration and velocity and travel a greater distance during fast-start swimming trials. However, velocity and distance traveled decline more rapidly over the course of pregnancy in these same females, thus reducing the magnitude of divergence in swimming performance between high- and low-predation populations. This functional trade-off between reproduction and swimming performance reveals how different aspects of the phenotype are integrated and highlights the complexity of adaptation at the whole-organism level.     

Exhaustive exercise does not affect the preferred temperature for recovery in juvenile rainbow trout (Oncorhynchus mykiss)

We tested the hypothesis that juvenile rainbow trout (Oncorhynchus mykiss) would select a temperature colder than their acclimation temperature (16 deg +/-1 deg C) to minimize postexhaustive exercise metabolic demands and enhance oxygen availability. After an initial 3-h exploratory period in a thermal gradient (6 degrees -25 degrees C), fish selected a temperature of approximately 14 degrees C and had a baseline exploratory swimming activity of approximately 60 cm min(-1). Subsequently, experimental (chased) fish were individually removed, exhaustively exercised for 1.5 min, and replaced. Both control (unchased) and experimental fish were allowed to explore the thermal gradient for another 2 h. Immediately after being chased, trout had a metabolic profile that was consistent with being exhausted; levels of plasma and muscle lactate were 4.38+/-0.25 mmol L(-1) and 28.0+/-2.0 mmol kg(-1), respectively, and levels of muscle glycogen, adenosine triphosphate, and phosphocreatine were 3.89+/-0.95, 4.23+/-0.62, and 3.07+/-0.73 mmol kg(-1), respectively. Although exploratory swimming activity of the chased fish was significantly lower (by 81%) as compared with control fish during the first 5 min postchase, differences in the mean, median, and mode values for selected temperatures during the next 2 h were neither large (<1 degrees C) nor significant (P>0.05). Contrary to our initial hypothesis, these findings suggest that juvenile rainbow trout do not select a colder temperature to decrease metabolic rate following exhaustive exercise. Instead, rainbow trout selected a temperature marginally cooler than their acclimation temperature (16 degrees C) regardless of whether they had been previously exhausted.