Individual and group behavioral responses to nutritional state and context in a social fish.

Understanding how animal collectives and societies form and function is a fundamental goal in animal biology. To date, research examining fish shoaling behavior has focused mostly on the general principles and ecological relevance of the phenomeon, while the ways in which physiological state (e.g., nutrition) affects collective behavior remain overlooked. Here, we investigated the shoaling behavior of common minnows (Phoxinus phoxinus) with three different nutritional states (control treatment: fasting for 24 h, fasting treatment: fasting for 7 days, and digestion treatment: 1 h after satiation feeding) across two ecological contexts (i.e., without and with food). No effects of either nutritional state or context were found on swimming speed, but the acceleration was greater in the digestion group than in the control group, with that in the fasting group being intermediate. Similar to change tendency in group length and group width of shoals, both interindividual distance and nearest neighbor distance were also greater in the fasting group than in the digestion group, suggesting that fasting and digestion may exert opposite driving forces on group cohesion. However, neither nutritional state nor context influenced the group area, group speed, group percent time moving, or group polarization. Both the foraging efficiency and the percentage of food items consumed by the fish shoals were greater in the fasting and control groups than in the digestion group. Our study suggested that one week of hunger and the energetically demanding stage of food digestion tend to have opposite influences on group shape, while the social foraging context does not influence the individual and group behavior of fish.

Effects of external cues and group mate body size on the collective behavior of shoaling crucian carp.

Chemical alarm cues (CACs) play a key role in the predatorprey relationship in fish. Chemical cues in the aquatic environment have an impact on the individual and group behavior of fish, and differences in these behavioral responses might be related to the body size of group members. Here, we used juvenile crucian carp (Carassius carassius) as an animal model to examine the effects of different cues and group mate body sizes on the individual and group behavior of shoaling fish. Three group mate body size (small, large, and mixed size) and three pheromone (rearing tank water, food, and CACs) treatments were combined in our study, with each treatment having 16 groups of five fish. We found that the individual swimming speed of the mixed group increased after injecting rearing water and food cues in the tank. After injecting CACs, the individual swimming speed of both the small and mixed groups increased, while that of the large group did not change. After the injection of CACs, the group speed of the small group was higher than that of the large and mixed groups. After the food cues were added to the tank, the synchronization of speed of the small group was higher than that of the mixed and large groups. Both the interindividual distance and nearest-neighbor distance of the mixed group remained unchanged after injecting CACs. Our study indicated that the impact of external cues on the individual and collective behavior of fish is related to the difference in body size of group mates.

Social isolation does not alter the relationship between flexibility in metabolic rate and growth in grass carp (Ctenopharyngodon idella) under changing food availability.

Growth and energy metabolism are highly flexible in fish species in response to food availability, and these two traits depend to some extent on the social rearing environment (e.g., isolated vs. group rearing). Currently, how social rearing environments influence flexibility in metabolic rate of fish and their ecological consequences (e.g., somatic growth) remain largely unknown. Here, we investigated how social isolation (i.e., group-reared vs. isolation-reared) and food availability (i.e., high vs. low) affect metabolic rates, growth and their correlations in a group-living fish, grass carp (Ctenopharyngodon idella), which were subjected to a 4-week growth experiment. The metabolic rates (e.g., standard metabolic rate, SMR; maximum metabolic rate, MMR; aerobic scope, AS = MMR-SMR) and morphology (e.g., body mass and length) of the fish in four treatments were measured at the beginning and end of the growth experiment, and then the growth parameters (e.g., food intake, FI; feeding efficiency, FE; and specific growth rate, SGR) were also obtained. We found that social isolation did impair growth of fish with individuals showing a lower SGR compared to those group-reared fish irrespective of food availability. However, the growth advantage of group-reared fish under two food availabilities did not result from their FIs or FEs. Metabolic rates (i.e., SMR) seemed to decrease in response to social isolation, but increased greater when fish were reared at high food ration. These shifts in metabolic rates were positively linked with individual differences in somatic growth; individuals who increased metabolic rates more grew faster, while those who increased their metabolic rates less or even reduced had a lower growth, but these links were independent on both social isolation and food ration. These results suggested that social isolation can inhibit the growth of individual fish, but not the AS. Flexibility in metabolic rates could confer a growth advantage under changing food availability, but the links between variation in energy metabolism and growth were not altered by social deprivation. Our study demonstrates the importance of metabolic plasticity accounting for inter-individual difference in growth performance under the challenges of changing food resource.

Previous experience alters individual vulnerability to angling of crucian carp (Carassius auratus).

In recreational fisheries, fish often undergo catch-and-release angling, which can lead to an indirect selection response of the behavioral traits of the fish. As individuals experience high-intensity angling activities, individuals learn to avoid being selected for artificial bait again, resulting in a change in the vulnerability to angling of fish, which is partly dependent on the cognitive learning ability of the fish. Here, we examined the relationship between vulnerability to angling and learning in juvenile crucian carp (Carassius auratus) under laboratory conditions. Our study had six angling treatments with each containing different group mates (i.e., the angling stress group, all fish that only experienced repeated angling stress practice for a period of three days; the learning group, all fish that only observed individual in the angling stress group to be angled; the control group, all fish that did not undergo any angling or learning; the mixed Group 1, fish are from the control and learning groups; the mixed Group 2, fish are from the control and angling stress groups; the mixed Group 3, fish are from the learning and angling stress groups), each of which consisted of five replicates). All fish were tested for boldness before and after the previous experiences (i.e., angling stress or learning) test. Our results showed that for the stress group, the total angling time, mean individual angling time and total number of bait touches all increased from Day 1 to Day 3, and the total angling rate decreased during the three days of the angling stress practice. After encountering the previous experiences, fish in the control, stress and learning groups all had increased boldness, as assessed by a shortened percent latency to emerge from the refuge. The change in the percent latency of boldness was higher in the stress group than in the learning group, with the control group being intermediate. Furthermore, no differences in the total angling time and total number of bait touches were detected among the six angling treatments, but the stress group exhibited the longest mean individual angling time and lowest angling rate compared with the other five angling treatments, indicating that angling-stressed individuals greatly decreased their vulnerability to angling after the previous angling stress. Our results show that changes in the vulnerability of crucian carp to angling were related to previous individual angling experience but not to visual social learning.

Predator stress decreases standard metabolic rate and growth in juvenile crucian carp under changing food availability.

Animals adapt to the challenges of fluctuations in predator risk and food availability in their natural habitats. Phenotypic plasticity allows animals to handle environmental changes. However, the patterns of flexibility in metabolic rates and its ecological consequences under different predator stress and food availability conditions are poorly understood. Here, we used crucial carp (Carassius auratus) as a prey species and northern snakehead (Channa argus) as a predator to test whether predator stress influences metabolism and growth, and alters the link between flexibility in metabolic rate and its ecological consequences (e.g., growth) in crucial carp. The experiment was carried out under the conditions of predator stress (with or without a predator) and three food availabilities (satiation feeding 1 time per day, low food availability; 2 times per day, intermediate food availability; and 3 times per day, high food availability) for 3 weeks. After 21 days of feeding, the final body mass and body length in the two treatments increased compared to the initial values in all three food availabilities. The feeding intake (FI) and specific growth rate (SGR) of the two treatments increased with increasing food availability. The control treatment had a higher FI and SGR than the predator stress treatment in all three food availabilities. The feeding efficiency (FE) of the two treatments was higher at the high and intermediate food availabilities than at the low food availability. However, no effect of predator stress on FE was detected. The final values of original or standardized SMR were higher in the control treatment than the predator stress treatment at the intermediate and high food availabilities. The changes in SMR (ΔSMR) were higher in the control treatment than in the predator stress treatment. The positive correlation between the ΔSMR and SGR was found in the intermediate food availability in the predator stress treatment, suggesting that individuals with a higher flexibility in SMR had a larger growth rate and vice versa, but this relationship was dependent on food availability. Our results suggest that predator stress decreased maintenance metabolism, feeding and growth of juvenile crucial carp irrespective of food availability. Predator stress does not alter the growth advantages conferred by the metabolic plasticity of the fish under changing food availability.

The effects of temperature and food availability on growth, flexibility in metabolic rates and their relationships in juvenile common carp.

Flexibility in phenotypic traits can allow organisms to handle environmental changes. However, the ecological consequences of flexibility in metabolic rates are poorly understood. Here, we investigated whether the links between growth and flexibility in metabolic rates vary between two temperatures. Common carp Cyprinus carpio were raised in three temperature treatments [the 18°C, 28°C and 28°C-food control (28°C-FC)] and fed to satiation of receiving food either once or twice daily for 4weeks. The morphology and metabolic rates (standard metabolic rate, SMR; maximum metabolic rate, MMR) were measured at the beginning and end of the experiment. The mean total food ingested by fish in the 28°C-FC treatment was the same as that by fish in the 18°C treatment at each food availability. The final SMR (not MMR and aerobic scope, AS=MMR-SMR) increased more in the 28°C and 28°C-FC treatments with twice-daily feedings than once-daily feedings. Fish in the 28°C treatment had a higher specific growth rate (SGR) than fish in the 28°C-FC and 18°C treatments at both food availabilities. However, no differences in feeding efficiency (FE) were found among the three treatments in fish fed twice daily. The flexibility in SMR was related to individual differences in SGR, not with food intake and FE; individuals who increased their SMR more had a smaller growth performance with twice-daily feedings at 28°C, but it did not exist at 18°C. Flexibility in SMR provides a growth advantage in juvenile common carp experiencing changes in food availability and this link is temperature-dependent.

Does aerobic capacity predict the spatial position of individuals within schools in juvenile qingbo (Spinibarbus sinensis)?

Schooling behavior is an adaptive trait of important biological and ecological significance in fish species. However, the question of how aerobic capacity and environmental factors (i.e., food and water velocity) affect the spatial positioning within fish schools has received little attention. Our study measured the aerobic capacity-as indicated by standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS)-and swimming performance of juvenile qingbo (Spinibarbus sinensis) and filmed their schooling behavior in a swim tunnel under both a control treatment and food stimulus treatment at three water velocities (20, 30 and 40cms-1). Neither aerobic capacity nor swimming performance was related to spatial position within schools. Food stimulation did not trigger any change in the characteristics of spatial position at three water velocities. However, an intra-school positional preference was found between water velocities under the control treatment and food stimulus treatment. Individuals who preferred the rear of the school had smaller coefficients of variation in position under the two treatments, but this behavior was not correlated with any parameters for metabolic rates. Inter-school social interaction level, as indicated by total chase times, was not affected by either water velocity or food appearance. Although aerobic capacity and food stimulus did not influence the spatial position of individuals within schools, individual qingbo had spatial positional preferences within schools between different water speeds.

Standard metabolic rate predicts growth trajectory of juvenile Chinese crucian carp (Carassius auratus) under changing food availability.

Phenotypic traits vary greatly within populations and can have a significant influence on aspects of performance. The present study aimed to investigate the effects of individual variation in standard metabolic rate (SMR) on growth rate and tolerance to food deprivation in juvenile Chinese crucian carp (Carassius auratus) under varying levels of food availability. To address this issue, 19 high and 16 low SMR individuals were randomly assigned to a satiation diet for 3 weeks, whereas another 20 high and 16 low SMR individuals were assigned to a restricted diet (approximately 50% of satiation) for the same period. Then, all fish were completely food-deprived for another 3 weeks. High SMR individuals showed a higher growth rate when fed to satiation, but this advantage of SMR did not exist in food-restricted fish. This result was related to improved feeding efficiency with decreased food intake in low SMR individuals, due to their low food processing capacity and maintenance costs. High SMR individuals experienced more mass loss during food deprivation as compared to low SMR individuals. Our results here illustrate context-dependent costs and benefits of intraspecific variation in SMR whereby high SMR individuals show increased growth performance under high food availability but had a cost under stressful environments (i.e. food shortage).

The relationship between growth performance and metabolic rate flexibility varies with food availability in juvenile qingbo (Spinibarbus sinensis).

Phenotypic flexibility in traits can allow organisms to cope with environmental challenges. However, the ecological consequences (e.g., growth) of SMR flexibility in fish are poorly understood. Juvenile qingbo (Spinibarbus sinensis) were reared individually with two levels of food resources (satiation or limited) with either continuous feeding (CF) or starvation-refeeding (SR). In the CF experiment, SMR increased when individuals were fed either the satiation or limited diets, but no difference was found in average specific growth rate somatic growth (SGR) between the two food availabilities. The relationship between flexibility in SMR and SGR, feeding efficiency (FE) and food intake (FI) was positive in the satiation group but not in the limited food group. In the SR experiment, the initial SMR of individuals was negatively correlated with the SGR during starvation. During refeeding, the starved individuals increased both body mass and SMR under both food availabilities. Individuals with a greater increase in SMR were fed more and also had greater SGR and FE under the satiation diet, but these results were not observed under the limited diet. The average FE under the limited diet was greater than that under the satiation diet, causing there to be no significant difference in final body mass between the diet treatments at the end of refeeding. Our study suggested that SMR flexibility can allow individuals to maximize their potential growth performance in an environment with changing food availability, and the benefits from greater flexibility in SMR could be offset by their maintenance metabolism under environmental stress.

[Effects of dexmedetomidine on microcirculatory perfusion in rabbits with renal ischemia/reperfusion injury: quantitative evaluation with contrast-enhanced ultrasound].

OBJECTIVE: To investigate the effects of dexmedetomidine on renal microcirculatory perfusion in rabbits with renal ischemia/reperfusion (I/R) injury rabbit by quantitative analysis of contrast-enhanced ultrasound (CEUS). METHODS: Twenty- four New Zealand rabbits were randomly divided into 3 groups (8 in each), including a control group, renal I/R injury group and dexmedetomidine group. In the latter two groups, the right kidney of the rabbits was resected and I/R injury was induced in the left kidney. In dexmedetomidine group, the rabbits received an intraperitoneal dose of 10 µg/kg dexmedetomidine 30 min before renal ischemia, and 24 h after reperfusion, the renal size and renal artery resistance (RI) were measured, and renal cortex perfusion was observed by CEUS. The time-to-peak intensity (TTP), peak signal intensity (PSI), gradient between start frame to peak frame (Grad) and area under the curve (AUC) were quantitatively analyzed using the time-intensity curves. Pathological changes of the kidney were also observed. RESULTS: Compared with the control group, the rabbits in I/R and dexmedetomidine groups showed distinct changes of the renal size with obvious renal pathologies. RI, PPT and AUC all increased, and PSI and Grad decreased significantly in I/R and dexmedetomidine groups (P<0.05). Compared with I/R group, obvious improvement of the renal size and renal pathologies were observed in dexmedetomidine group, which showed significantly decreased RI, PPT and AUC and increased PSI and Grad (P<0.05). CONCLUSION: CEUS combined with the time-intensity curve parameters allows quantitative and dynamic analysis of the protective effects of dexmedetomidine on microcirculatory perfusion in rabbits with renal I/R injury.

Physiological and morphological responses to the first bout of refeeding in southern catfish (Silurus meridionalis).

Many animals experience fasting because of the high temporal and spatial sporadicity of food availability. Once food is available, animals use external energy to restore their depressed functional performance. In the present study, the physiological and morphological responses to the first bout of refeeding in juvenile southern catfish (Silurus meridionalis) were characterized. Fish that had undergone long-term fasting (fasted for 32 days, the S32 group) exhibited a lower resting metabolic rate (MO(2rest) decreased by 49%), lower peak metabolic rate (MO(2peak) decreased by 24%), greater energy expenditure (increased by 15%) during specific dynamic action (SDA) and longer duration SDA response (increased by 41%) than those of a control group (S0 group, fasted for 0 days). The S32 group showed a significantly reduced peak gastric evacuation rate (0.131 g meal h(-1)) compared with the S0 group (0.315 g meal h(-1)). The S0 group also had a shorter gastric evacuation time (36 h) than either of the two fasting groups (both 64 h). The S32 group displayed a higher minimum gastric pH (3.1) than the S0 and S16 groups (2.6). Refeeding did not trigger an increase in the wet mass of the gastrointestinal tract, whereas the liver wet mass of the S0 and the two fasting groups increased significantly with refeeding. The trypsin and lipase of the S0 group showed higher mass-specific activities and organ capacities than either of the two fasting groups at certain specific time points. A similar result was found for aminopeptidase activity. Multiple loach meals equaling 6% of the body weight of the fed fish completely restored the liver morphology within the S16 but not the S32 group. Our results suggest that the regulation of the digestive performance of the gastrointestinal tract in S. meridionalis that are finishing their first small meal after fasting is delayed compared with that of nonfasting fish and that it is similar to the characteristics (lower MO(2peak), greater SDA and a longer duration of the SDA response) of the refeeding SDA.

The effect of aerobic exercise training on growth performance, digestive enzyme activities and postprandial metabolic response in juvenile qingbo (Spinibarbus sinensis).

Continual swimming exercise usually promotes growth in fish at a moderate water velocity. We hypothesized that the improvement in growth in exercise-trained fish may be accompanied by increases in digestive enzyme activity, respiratory capacity and, hence, postprandial metabolism. Juvenile qingbo fish (Spinibarbus sinensis) were subjected to aerobic training for 8weeks at a water velocity of control (3cms(-1)), 1, 2 and 4 body length (bl)s(-1) at a constant temperature of 25°C. The feed intake (FI), food conversion rate (FCR), specific growth rate (SGR), whole-body composition, trypsin and lipase activities, maximal oxygen consumption (M˙O2max) and postprandial M˙O2 response were measured at the end of the training period. Aerobic exercise training induced a significant increase in FI compared with the control group, while the FCR of the 4bls(-1) group was significantly lower than for the other three groups (P<0.05). The 1 and 2bls(-1) groups showed a significantly higher SGR over the control group (P<0.05). The whole-body fat and protein contents were significantly altered after aerobic exercise training (P<0.05). Furthermore, aerobic exercise training elevated the activity of both trypsin and lipase in the hepatopancreas and intestinal tract of juvenile S. sinensis. The M˙O2max of the 4bls(-1) training group was significantly higher than for the control group. The resting M˙O2 (M˙O2rest) and peak postprandial M˙O2 (M˙O2peak) in the three training groups were significantly higher than in the control group (P<0.05). Time to M˙O2peak was significantly shorter in the 1, 2 and 4bls(-1) training groups compared with the control group, while exercise training showed no effect on SDA (specific dynamic action) duration, factorial metabolic scope, energy expended on SDA and the SDA coefficient when compared to the control group. These data suggest that (1) the optimum water velocity for the growth of juvenile S. sinensis occurred at approximately 2.4bls(-1); (2) the improvement of growth may have been primarily due to an increase in the FI after long-term training; (3) and aerobic exercise training boosted the activity of digestive enzymes and maximum digestive metabolism, which could favor fast digestion and growth in juvenile S. sinensis.

Effect of feeding on the function and structure of the digestive system in juvenile southern catfish (Silurus meridionalis Chen).

Postprandial physiological and morphological responses to feeding were examined in juvenile southern catfish (Silurus meridionalis Chen) that had consumed a loach (Misgurnus anguillicaudatus Cantor) meal equivalent to 6 % of the body mass of the catfish. The gastric evacuation rate (GER) peaked at 4 h postfeeding, averaging 0.36 g food weight h(-1), at which time 14 % of the ingested meal had passed into the intestine. Less than 10 % of the ingested meal remained in the stomach at 24 h postfeeding. Pepsin activity peaked at 8 h postfeeding, reaching a level approximately twofold higher than the prefeeding level. Pancreatic trypsin activity peaked at 16 h postfeeding, reaching a level 4.5-fold higher than the prefeeding level. Peaks in lipase activity in both the proximal and middle intestinal segments occurred at 16 h, reaching 2.8- and 2.4-fold higher levels than the prefeeding level, respectively, while the activity in the distal intestine segment reached a level 2.9-fold higher than the prefeeding level at 24 h postfeeding. With respect to amylase activity, only the middle intestinal segment exhibited a change, first an increase and then a decrease, after feeding. Feeding also triggered an approximately 200 % increase in the metabolic rate and resulted in 44.6 kJ kg(-1) being expended on specific dynamic action, equivalent to 16.1 % of the meal's energy. In terms of organ size, the wet mass of the liver increased by 11 % at 24 h postfeeding, whereas the wet mass of the pancreas did not change. Except for a decrease in the thickness of the submucosa in the middle intestinal segment, the thickness of the intestinal fold, mucosa, submucosa, muscularis and serosa of each intestinal segment did not change significantly with feeding. These results suggest that the continuum of physiological responses observed with respect to metabolic increases, GER, regulation of pancreatic and intestinal digestive enzyme activities and liver wet mass to feeding corresponds to the changes in the demand on the digestive system in S. meridionalis. Moreover, species maintained stable gastrointestinal tract morphology during the short interval of repeated feeding.

The effects of starvation on digestive tract function and structure in juvenile southern catfish (Silurus meridionalis Chen).

The size and functional capacity of the gastrointestinal (GI) tract and associated organs vary in response to environmental cues. The GI tract and associated organs are also very metabolically active in animals. Hence, animals may reduce the size and function of their GI tract to conserve energy when deprived of food. The main aims of this study were to investigate how Silurus meridionalis regulates the function and structure of its GI tract and associated organs during starvation. Starvation induced a decrease in both maintenance metabolism (MO(2rest), decreased by approximately 50%) and respiratory frequency (indicated by double side gill activity and notated as f(R), decreased by 29%). Lipase, trypsin and aminopeptidase-A showed a similar reduction in mass-specific activities during starvation, but pepsin and α-amylase did not. The starvation of experimental fish resulted in a significant reduction in body weight, the wet mass of the liver and the digestive-somatic system, the hepato-somatic index and the condition factor whereas the wet masses of the GI tract, pancreas, gall bladder and the relative intestinal length did not vary significantly during starvation. The reduction in liver wet mass was the main reason for the decrease in the wet mass of digestive-somatic system in this species. Only the mucosal area of the PI was affected significantly by starvation, decreasing by 34% at the end of the experiment. S. meridionalis displayed a decreasing intestinal mucosal area towards the distal intestine, and this gradient was not affected by starvation. The morphology and structure of both the GI tract and the liver were greatly down-regulated, as indicated by decreases in liver cell size, the mucosal thickness of the stomach and intestine, the density of goblet cells and microvilli surface area (MVSA), implying that food deprivation greatly impaired the digestive and absorptive functions of the GI tract in S. meridionalis. When deprived of food, S. meridionalis can endure harsh periods of starvation and adaptively down-regulate the function and structure of the digestive tract with physiological and biochemical strategies.

Effect of temperature on excess post-exercise oxygen consumption in juvenile southern catfish (Silurus meridionalis Chen) following exhaustive exercise.

The effects of temperature on resting oxygen consumption rate (MO2rest) and excess post-exercise oxygen consumption (EPOC) after exhaustive exercise (chasing) were measured in juvenile southern catfish (Silurus meridionalis) (8.40±0.30 g, n=40) to test whether temperature has a significant influence on MO2rest, maximum post-exercise oxygen consumption rate (MO2peak) and EPOC and to investigate how metabolic scope (MS: MO2peak - MO2rest) varies with acclimation temperature. The MO2rest increased from 64.7 (10°C) to 160.3 mg O2 h(-1) kg(-1) (25°C) (P<0.05) and reached a plateau between 25 and 30°C. The post-exercise MO2 in all temperature groups increased immediately to the peak values and then decreased slowly to a steady state that was higher than the pre-exercise MO2. The MO2peak did not significantly differ among the 20, 25 and 30°C groups, though these values were much higher than those of the lower temperature groups (10 and 15°C) (P<0.05). The duration of EPOC varied from 32.9 min at 10°C to 345 min at 20°C, depending on the acclimation temperatures. The MS values of the lower temperature groups (10 and 15°C) were significantly smaller than those of the higher temperature groups (20, 25 and 30°C) (P<0.05). The magnitude of EPOC varied ninefold among all of the temperature groups and was the largest for the 20°C temperature group (about 422.4 mg O2 kg(-1)). These results suggested that (1) the acclimation temperature had a significant effect on maintenance metabolism (as indicated by MO2rest) and the post-exercise metabolic recovery process (as indicated by MO2peak, duration and magnitude of EPOC), and (2) the change of the MS as a function of acclimation temperature in juvenile southern catfish might be related to their high degree of physiological flexibility, which allows them to adapt to changes in environmental conditions in their habitat in the Yangtze River and the Jialing River.

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.

The behavioural, digestive and metabolic characteristics of fishes with different foraging strategies.

To test the hypothesis that digestion has a more notable physiological effect on ambush foragers than on active foragers, we investigated the behavioural, digestive and metabolic characteristics, as well as the postprandial locomotory capacity, of four species of juvenile fish distributed along the Yangtze River, China, with distinct foraging strategies. The ambush foraging southern catfish (Silurus meridionlis) had the fewest movements per minute (MPM), lowest per cent time spent moving (PTM), slowest critical swimming speed (Ucrit), lowest maintenance metabolism (VO2rest) and lowest maximum locomotory metabolism (VO2max)). However, the southern catfish had the highest feeding level and maximum feeding metabolism (VO2peak) and the greatest decrease in Ucrit after consumption of a large meal. Thus, this fish is highly adapted to its ambush behavioural strategy and sedentary life style. In the herbivorous grass carp (Ctenopharyngodon idellus), a low digestive capacity led to little change in postprandial locomotory performance, which benefits its frequent grazing behaviour. In this species, the greater amount of energy spent on routine activity and avoiding predators versus Ucrit might be related to its herbivorous life style and high predation risk. The active foraging crucian carp (Carassius auratus) adopts a unique high energy cost strategy that allows for high capacity in both routine activity and digestion, and the great flexibility of its cardio-respiratory capacity (increased VO2max after feeding) guarantees a small decrease in Ucrit even after maximum feeding. Finally, the sluggish foraging darkbarbel catfish (Pelteobagrus vachelli) has low digestive and locomotory capacity, but its energy-efficient venomous defence strategy may be related to its abundance. These results show that the digestive, behavioural and metabolic strategies differ among these fish species. The locomotory capacity in the sedentary fishes decreased profoundly after feeding, whereas it decreased little or not at all in the active fishes. The maintenance of high locomotory capacity after eating in the active fishes is probably related to a large metabolic capacity, a lower digestive capacity or an improvement in cardio-respiratory capacity after feeding.

Effect of meal size on excess post-exercise oxygen consumption in fishes with different locomotive and digestive performance.

Effects of feeding on pre-exercise VO(2) and excess post-exercise oxygen consumption (EPOC) after exhaustive exercise were investigated in sedentary southern catfish, active herbivorous grass carp, omnivorous crucian carp, and sluggish omnivorous darkbarbel catfish to test whether feeding had different effects on EPOC and to compare EPOC in fishes with different ecological habits. For fasting fish, the pre-exercise and peak post-exercise VO(2) were higher and recovery rates were faster in crucian carp and grass carp compared to those of darkbarbel catfish and southern catfish. EPOC magnitudes of grass carp and southern catfish were significantly larger than those of crucian carp and darkbarbel catfish. Feeding had no significant effect on peak post-exercise VO(2), recovery rate, and EPOC magnitude in grass carp. Both the pre-exercise and peak post-exercise VO(2) increased with meal size, while the EPOC magnitude and duration decreased significantly in the larger meal size groups of crucian carp and southern catfish. In darkbarbel catfish, both the pre-exercise and peak post-exercise VO(2) increased with meal size, but the VO(2) increment elicited by exercise was larger in feeding groups compared with the fasting group. These results suggest that (1) the characteristics of the post-exercise VO(2) profile, such as peak post-exercise VO(2) and recovery rate, were closely related to the activity of fishes, whereas the EPOC magnitude was not and (2) the effects of feeding on EPOC were more closely related to the postprandial increase in VO(2).