Predation experience underlies the relationship between locomotion capability and survival.

The positive relationship between locomotion performance and survival under predation has long been suggested yet seldom demonstrated with direct evidence. We investigate the effects of predator exposure on locomotion capacity (both fast-start escape and critical swimming performance), survival under predation and the relationships between these factors in juvenile Chinese bream (Parabramis pekinensis). This study aims to test whether there is a positive relationship between the above factors and whether such relationships are context dependent (i.e., with or without 20 d of predator exposure). We found that predator-exposed Chinese bream showed higher rates of survival under predation and improved fast-start swimming performance compared with individuals not exposed to predation. At individual level, no relationship was found between survival and any locomotion performance component in the no-predator group, but mean fast-start swimming speed, maneuverability and responsiveness were all positively related to survival in the predator group after 20 d of exposure. This finding indicates that the recognition of and vigilance for predators achieved through predation experience can be crucial preconditions for prey to employ the fast-start escape response, especially to escape ambush predators. Furthermore, a tradeoff was observed between the critical and fast-start swimming performances in the predator group, but not in the no-predator group, which may have been due to the intensified competition throughout the entire locomotion-support system (e.g., energy, proportions of slow- and fast-twitch muscle fibers) between critical and fast-start swimming because the increased demand for fast-start escape capacity constrains (or compromises) critical swimming performance under the threat of predation.

Digesting or swimming? Integration of the postprandial metabolism, behavior and locomotion in a frequently foraging fish.

Fish that are active foragers usually perform routine activities while digesting their food; thus, their postprandial swimming capacity and related behavior adjustments might be ecologically important. To test whether digestion affect swimming performance and the relationships of digestion with metabolism and behavior in an active forager, we investigated the postprandial metabolic response, spontaneous swimming activities, critical swimming speed (Ucrit), and fast-start escape performance of both fasted and digesting (3h after feeding to satiation) juvenile rose bitterling (Rhodeus ocellatus). Feeding to satiation elicited a 50% increase in the oxygen consumption rate, which peaked at 3h after feeding and returned to the prefeeding state after another 3h. However, approximately 50% and 90% of individuals resumed feeding behavior at 2 and 3h postfeeding, respectively, although the meal size varied substantially. Digestion showed no effect on either steady swimming performance as suggested by the Ucrit or unsteady swimming performance indicated by the maximum linear velocity in fast-start escape movement. However, digesting fish showed more spontaneous activity as indicated by the longer total distance traveled, mainly through an increased percentage of time spent moving (PTM). A further analysis found that fasting individuals with high swimming speed were more inclined to increase their PTM during digestive processes. The present study suggests that as an active forager With a small meal size and hence limited postprandial physiological and morphological changes, the swimming performance of rose bitterling is maintained during digestion, which might be crucial for its active foraging mode and anti-predation strategy.

A comparison of constant acceleration swimming speeds when acceleration rates are different with critical swimming speeds in Chinese bream under two oxygen tensions.

To investigate the effect of acceleration rates on the constant acceleration test speed (U cat) and to compare U cat with the critical swimming speed (U crit) in Chinese bream (Parabramis pekinensis), the U cat test at acceleration rates of 0.05, 0.1, 0.2, 0.4 and 0.8 cm s(-2) and the U crit test in juvenile fish at 20 °C in either normoxia (>90 % saturation oxygen tension) or hypoxia (30 % saturation) were compared. The lactate concentration ([lactate]) of white muscle, liver and plasma and the glycogen concentration ([glycogen]) of white muscle and liver were also measured to identify whether tissue substrate depletion or tissue lactate accumulation correlated with exhaustion. The U cat decreased with the acceleration rate, and there was no significant difference between U crit and U cat at lower acceleration rates. Hypoxia resulted in lower U cat and U crit, and the difference increased with decreased acceleration rates of the U cat test, possibly due to the increased contribution of aerobic components in U crit or U cat at low acceleration rates. Hypoxia elicited a significant decrease in muscle [glycogen] and an increase in muscle and liver [lactate] in resting fish. All post-exercise fish had similar muscle [lactate], suggesting that tissue lactate accumulation may correlate with exercise exhaustion. Unlike hypoxia, exercise induced an increase in muscle [lactate] and a significant increase in plasma [lactate], which were worthy of further investigation. The similar swimming speed and biochemical indicators after exercise in the U crit and U cat groups at low acceleration rates suggested that U cat can be an alternative for the more frequently adopted protocols in U crit in Chinese bream and possibly in other cyprinid fish species.

Predator-driven intra-species variation in locomotion, metabolism and water velocity preference in pale chub (Zacco platypus) along a river.

Fish inhabit environments that vary greatly in terms of predation intensity, and these predation regimes are generally expected to be a major driver of divergent natural selection. To test whether there is predator-driven intra-species variation in the locomotion, metabolism and water velocity preference of pale chub (Zacco platypus) along a river, we measured unsteady and steady swimming and water velocity preference among fish collected from both high- and low-predation habitats in the Wujiang River. We also measured the routine metabolic rate (RMR), maximum metabolic rate (MMR) and cost of transport (COT) and calculated the optimal swimming speed (Uopt). The fish from the high-predation populations showed a shorter response latency, elevated routine metabolism, lower swimming efficiency at low swimming speed and lower water velocity preference compared with those from the low-predation populations. Neither of the kinematic parameters fast-start and critical swimming speed (Ucrit) showed a significant difference between the high- and low-predation populations. The fish from the high-predation populations may improve their predator avoidance capacity primarily through an elevated routine metabolism and shorter response latency to achieve advanced warning and escape, rather than an improved fast-start swimming speed or acceleration. Thus, the cost of this strategy is an elevated RMR, and no trade-off between unsteady and steady swimming performance was observed in the pale chub population under various predation stresses. It was interesting to find that the high-predation fish showed an unexpected lower velocity preference, which might represent a compromise between predation avoidance, foraging and energy saving.

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

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

Effect of temperature on hypoxia tolerance and its underlying biochemical mechanism in two juvenile cyprinids exhibiting distinct hypoxia sensitivities.

It is increasingly important to investigate the effect of temperature on hypoxia tolerance in fish species, as worldwide hypoxia worsens with increases in global warming. We selected the hypoxia-tolerant crucian carp (Carassius carassius) and the hypoxia-sensitive Chinese bream (Parabramis pekinensis) as model fish and investigated their hypoxia tolerance based on the critical oxygen tension of the routine metabolic rate (M˙O2rout) (Pcrit), aquatic surface respiration (ASRcrit) and loss of equilibrium (LOEcrit) after two weeks of acclimation at either 10, 20 or 30 °C. We also measured the tissue substrate (glycogen and glucose of muscle and liver) and lactate levels of both normoxia- and hypoxia-treated fish (post-LOE). Crucian carp exhibited significantly lower Pcrit and LOEcrit but not ASRcrit. Crucian carp possessed higher hypoxia tolerance, partially due to a higher tissue glycogen reserve, which provides cellular fuel under severe hypoxia, as well as higher lactate tolerance and clearance ability than Chinese bream. The hypoxia tolerance was maintained in crucian carp but was decreased in Chinese bream as the temperature increased. The difference between the two species is based on the greater recruitment of tissue glycogen, resulting in an increased level of cellular fuel during hypoxia in crucian carp than in Chinese bream. In addition, crucian carp possessed the greater liver lactate clearance capacity, and the smaller increase in the M˙O2rout at higher temperatures compared to Chinese bream. Furthermore, substrate shortage and decreased lactate tolerance at high temperatures in Chinese bream might also contribute to the difference in hypoxia tolerance between the two species.

The effect of temperature on repeat swimming performance in juvenile qingbo (Spinibarbus sinensis).

To investigate the effect of temperature on the repeat constant acceleration swimming performance and on the metabolic recovery capacity in juvenile qingbo (Spinibarbus sinensis), their constant acceleration test speed (U(CAT)) and excess post-exercise oxygen consumption (EPOC) recovery process were measured twice with 1-h intervals at different acclimation temperatures (10, 15, 20, 25 and 30 °C). Temperature significantly affected U(CAT), the pre-exercise metabolic rate (MO(2)), metabolic peak values (MO(2peak)), the metabolic scope (MS, MO(2peak)--pre-exercise MO(2)) and the magnitude of the EPOC (P < 0.05). These parameters significantly increased as the temperature increased from 15 to 25 °C and significantly decreased (U(CAT) and EPOC magnitude) or did not change (MO(2peak) and MS) when the temperature increased from 25 to 30 °C in the first test (P < 0.05). The relationships between temperature (T) and these parameters (U(CAT), MO(2peak), MS and EPOC magnitude) in the first test were as follows: U(CAT) = 62.14/{1 + [(T - 25.1)/21.1](2)} (r = 0.847, P < 0.001, n = 40); MO(2peak) = 1,052.11/{1 + [(T - 29.2)/18.9](2)} (r = 0.901, P < 0.001, n = 39); MS = 753.74/{1 + [(T - 27.1)/18.6](2)} (r = 0.768, P < 0.001, n = 39); and EPOC = 195.42/{1 + [(T - 25.6)/8.7](2)} (r = 0.752, P < 0.001, n = 39). The optimal temperatures for U(CAT), MO(2peak), MS and EPOC magnitude in juvenile qingbo were 25.1, 29.2, 27.1 and 28.6 °C, respectively. Repeat exercise had different effect on U(CAT) and EPOC magnitude at different temperature (interaction effect, P < 0.05). There was no difference in U(CAT) and in EPOC magnitude between the first and second tests at low temperatures (10-20 °C). However, both U(CAT) and EPOC magnitude decreased significantly during the second test compared with the first test at high temperatures (25 and 30 °C) (P < 0.05). The present study showed that the recovery of the constant acceleration swimming performance was poorer at higher temperatures than at low temperatures in juvenile qingbo. These differences may be related to larger anaerobic metabolism, a lower pH value in the blood, larger ionic fluids and/or higher levels of hormones present at high temperatures.

Behavior, metabolism and swimming physiology in juvenile Spinibarbus sinensis exposed to PFOS under different temperatures.

The harmful effects of perfluorooctane sulfonate (PFOS) are of growing international concern. This paper aimed to gain an integrated understanding of fitness-related ecological end points, such as behavior, metabolism and swimming physiology, in juvenile Spinibarbus sinensis in response to PFOS toxicity at different temperatures. The fish were exposed to a range of PFOS concentrations (0, 0.32, 0.8, 2 and 5 mg/L) at different temperatures (18 and 28 °C) for 30 days. The effects on fish behavior, metabolic characteristics and aerobic swimming performance caused by PFOS at different temperatures were investigated. Our results showed that both PFOS and temperature had important influences on spontaneous swimming behavior, social interactions, routine metabolic rate (RMR), net energetic cost of transport (COTnet) and critical swimming speed (U crit) in fish. The lowest observed effect concentration for both U crit and RMR was 5 and 0.8 mg/L at 18 and 28 °C, respectively. We found that PFOS affected various behavioral and social end points and also appeared to affect metabolic rates and reduced U crit, likely as a result of increased COTnet, and that many of these effects also changed with respect to temperature. Our results further the understanding of the metabolic and behavioral toxicity of PFOS to aquatic organisms.

Interspecific variation in hypoxia tolerance, swimming performance and plasticity in cyprinids that prefer different habitats.

This study quantified and compared hypoxia tolerance and swim performance among cyprinid fish species from rapid-, slow- and intermediate-flow habitats (four species per habitat) in China. In addition, we explored the effects of short-term acclimation on swim performance, maximum metabolic rate (M(O2,max)) and gill remodelling to detect habitat-associated patterns of plastic response to hypoxia. Indices of hypoxia tolerance included oxygen threshold for loss of equilibrium (LOE50) and aquatic surface respiration (ASR50), and critical oxygen tension for routine metabolic rate (Pcrit). Critical swimming speed (Ucrit) and M(O2,max) were measured under normoxic and hypoxic conditions after 48 h acclimation to normoxia and hypoxia, and gill remodelling was estimated after 48 h of hypoxia exposure. Both traditional ANCOVA and phylogenetically independent contrast (PDANOVA) analyses showed that fish species from rapid-flow habitats exhibited lower LOE50 compared with fish from intermediate- and slow-flow habitats. Habitat-specific differences in Pcrit and Ucrit were detected using PDANOVA but not traditional ANCOVA analyses, with fish species from rapid-flow habitats exhibiting lower Pcrit but higher Ucrit values compared with fish from intermediate- and slow-flow habitats. Fish species from rapid-flow habitats were also characterized by less plasticity in swim performance and gill morphology in response to hypoxia acclimation compared with species from slow-flow habitats, but a greater drop in swim performance in response to acute hypoxia exposure. The study detected a habitat-specific difference in hypoxia tolerance, swimming performance and its plasticity among fish from habitats with different flow conditions, possibly because of the long-term adaptation to the habitat caused by selection stress. The PDANOVA analyses were more powerful than traditional statistical analyses according to the habitat effects in both hypoxia tolerance and swimming performance in this study.

The effects of constant and diel-fluctuating temperature acclimation on the thermal tolerance, swimming capacity, specific dynamic action and growth performance of juvenile Chinese bream.

We investigated the effects of constant and diel-fluctuating temperature acclimation on the thermal tolerance, swimming capacity, specific dynamic action (SDA) and growth performance of juvenile Chinese bream (Parabramis pekinensis). The critical thermal maxima (CTmax), critical thermal minima (CTmin), lethal thermal maxima (LTmax), lethal thermal minima (LTmin), critical swimming speed (Ucrit) and fast-start escape response after 30 d acclimation to three constant temperatures (15, 20 and 25 °C) and one diel-fluctuating temperature (20±5 °C) were measured. In addition, feeding rate (FR), feeding efficiency (FE) and specific growth rate (SGR) were measured. The diel-fluctuating temperature group showed lower CTmin than the 20 °C group but a similar CTmax, indicating a wider thermal scope. SDA linearly increased with the temperature. Temperature variation between 20 and 25 °C had little effect on either swimming or growth performance. However, fish in the 15 °C group exhibited much poorer swimming and growth performance than those in the 20 °C group. Ucrit decreased slightly under low acclimation temperature due to the pronounced improvement in swimming efficiency under cold temperature. Fish in the diel-fluctuating temperature group fed more but exhibited similar SGR compared to 20 °C group, possibly due in part to an increase in energy expenditure to cope with the temperature fluctuation. The narrower thermal scope and lower CTmax of Chinese bream together with the conservation of CTmax with temperature acclimation, suggests that local water temperature elevations may have more profound effects on Chinese bream than on other fish species in the Three Gorges Reservoir.

The effects of fasting on swimming performance in juvenile qingbo (Spinibarbus sinensis) at two temperatures.

We measured the following variables to investigate the effects of fasting and temperature on swimming performance in juvenile qingbo (Spinibarbus sinensis): the critical swimming speed (Ucrit), resting metabolic rate (MO2rest) and active metabolic rate (MO2active) of fish fasting for 0 (control), 1, 2 and 4 weeks at low and high acclimation temperatures (15 and 25°C). Both fasting treatment and temperature acclimation had significant effects on all parameters measured (P<0.05). Fasting at the higher temperature had a negative effect on all measured parameters after 1 week (P<0.05). However, when acclimated to the lower temperature, fasting had a negative effect on Ucrit until week 2 and on (MO2rest), (MO2active) and metabolic scope (MS, (MO2active)-(MO2rest)) until week 4 (P<0.05). The values of all parameters at the lower temperature were significantly lower than those at the higher temperature in the identical fasting period groups except for (MO2rest) of the fish that fasted for 2 weeks. The relationship between fasting time (T) and Ucrit was described as Ucrit(15)=-0.302T(2)-0.800T+35.877 (r=0.781, n=32, P<0.001) and Ucrit(25)=0.471T(2)-3.781T+50.097 (r=0.766, n=32, P<0.001) at 15 and 25°C, respectively. The swimming performance showed less decrease in the early stage of fasting but more decrease in the later stage at the low temperature compared to the high temperature, which might be related to thermal acclimation time, resting metabolism, respiratory capacity, energy stores, enzyme activity in muscle tissue and energy substrate utilization changes with fasting between low and high temperatures. The divergent response of the swimming performance to fasting in qingbo at different temperatures might be an adaptive strategy to seasonal temperature and food resource variation in their habitat.

The effects of caudal fin loss and regeneration on the swimming performance of three cyprinid fish species with different swimming capacities.

In nature, the caudal fins of fish species are frequently lost to some extent by aggressive behaviour, predation and diseases. To test whether the swimming performance of fish with different swimming capacities would be differentially affected due to caudal fin loss and regeneration, we investigated the critical swimming speed (Ucrit), swimming metabolic rate (M(O2)), tail beat frequency (f(TB)) and tail beat amplitude (A(TB)) after caudal fin loss and regeneration (20 days) in juveniles of three cyprinid fish species: the qingbo (Spinibarbus sinensis; strong swimmer), the common carp (Cyprinus carpio; intermediate swimmer) and the goldfish (Carassius auratus; poor swimmer). The Ucrit values of the caudal-fin-lost qingbo, common carp and goldfish were 49, 32 and 35% significantly lower than those of the control groups, respectively. The maximum tail beat amplitude (A(TBmax)) (all three fishes), the maximum tail beat frequency (f(TBmax)) (only the common carp and the goldfish) and/or the active metabolic rate (M(O2active)) (only the common carp) of the caudal-fin-lost fish were significantly higher than those of the control groups. After 20 days of recovery, the caudal fins recovered to 41, 47 and 24% of those of the control groups for the qingbo, the common carp and the goldfish, respectively. However, the Ucrit values of the fin-regenerated qingbo, common carp and goldfish recovered to 86, 91 and 95% of those of the control group, respectively. The caudal-fin-regenerated qingbo and common carp showed a significantly higher A(TBmax) and f(TBmax), respectively, compared with those of the control groups. The qingbo had a higher f(TBmax) but a lower A(TBmax) than the common carp and the goldfish, which suggested that a strong swimmer may maintain swimming speed primarily by maintaining a greater f(TBmax), for which the caudal fin plays a more important role during swimming, than a poor swimmer. The M(O2active) of fish (common carp) with a redundant respiratory capacity could increase due to caudal fin loss to meet the increase in energy expenditure required by an increase in f(TBmax). In addition, the sustained swimming performance may not be the only selective pressure acting on caudal fin size in these three species, and the present caudal fin size may be a trade-off between sustain swimming performance and other factors (e.g. sexual selection, escape responses).

Integrating environmental variation, predation pressure, phenotypic plasticity and locomotor performance.

The Wujiang River, a tributary of the Three Gorges Reservoir, has many dams along its length. These dams alter the river's natural habitat and produce various flow regimes and degrees of predator stress. To test whether the swimming performance and external body shape of pale chub (Zacco platypus) have changed as a result of alterations in the flow regime and predator conditions, we measured the steady (U(crit)) and unsteady (fast-start) swimming performances and morphological characteristics of fish collected from different sites along the Wujiang River. We also calculated the maximum respiratory capacity and cost of transport (COT). We demonstrated significant differences in swimming performance and morphological traits among the sampling sites. Steady swimming performance was positively correlated with water velocity and negatively correlated with the abundance of predators, whereas unsteady swimming performance was negatively correlated with water velocity. The body shape was significantly correlated with both swimming performance and ecological parameters. These findings suggested that selection pressure on swimming performance results in a higher U(crit) and a more streamlined body shape in fast-flow and (or) in habitats with low predator stress and subsequently results in a lower COT. These characteristics were accompanied by a poorer fast-start performance than that of the fish from the slow-flow and (or) high-predator habitats. The divergence in U(crit) may also be due in part to variation in respiratory capacity.

The effects of diel-cycling hypoxia acclimation on the hypoxia tolerance, swimming capacity and growth performance of southern catfish (Silurus meridionalis).

To investigate the effects of diel-cycling hypoxia acclimation on the hypoxia tolerance, swimming and growth performance of juvenile southern catfish, we initially measured the critical oxygen tension (P(crit)), oxygen thresholds of aquatic surface respiration (ASR) and loss of equilibrium (LOE) of diel-cycling hypoxia-acclimated (15 d, 7:00-21:00, dissolved oxygen level (DO) = 7.0 ± 0.2 mg L(-1); 21:00-7:00, DO = 3.0 ± 0.2 mg L(-1)) and non-acclimated (15 d, DO = 7.0 ± 0.2 mg L(-1)) southern catfish at 25 °C. We then measured the critical swimming speed (U(crit)) and metabolic rate (MR) of hypoxia-acclimated and non-acclimated fish (under both hypoxic and normoxic conditions). The feeding rate (FR), feeding efficiency (FE) and specific growth rate (SGR) of fish in hypoxia-acclimated and non-acclimated groups were also measured. The P(crit), ASR and LOE of hypoxia-acclimated fish were significantly lower than those of non-acclimated fish. Hypoxia acclimation resulted in a significantly higher U(crit) when the individuals swam in hypoxia. The U(crit), maximum metabolic rate (MMR) and metabolic scope (MS) of both the hypoxia-acclimated and non-acclimated fish all decreased with the decrease of DO. However, the U(crit), MMR and MS decreased by 31, 43 and 54%, respectively, in non-acclimated fish, whereas these values decreased by 15, 28 and 29%, respectively, in hypoxia-acclimated fish, which suggests that hypoxia-acclimated fish were less sensitive to the DO decrease. The FR, FE and SGR all decreased by 21, 20 and 45%, respectively, in the hypoxia-acclimated group compared to the non-acclimated group. This result suggests that diel-cycling hypoxia acclimation improved the hypoxia tolerance and aerobic swimming performance of southern catfish, whereas impaired the growth performance. The high hypoxia tolerance and physiological plasticity to hypoxia-acclimated southern catfish may be related to its lower maintenance energy expenditure, sit-and-wait lifestyle and bottom-dwelling living environment condition (usually facing oxygen fluctuation). The growth performance of so-called 'visceral type' fish species, such as southern catfish, are more sensitive to hypoxia compared to other fish species because of their high peak post-prandial metabolic rate, which may be restrained by the limited aerobic metabolic scope in hypoxia.

The effects of caudal fin amputation on metabolic interaction between digestion and locomotion in juveniles of three cyprinid fish species with different metabolic modes.

Metabolic competitive modes between digestion and locomotion are classified into three categories, termed the additive, digestion- and locomotion-priority modes. In nature, the caudal fin is frequently observed to sustain damage as a result of social rank, predation or disease. To test whether the metabolic mode changed differently for fish with different metabolic mode after caudal fin amputation as a consequence of intensified energy competition, we investigated the swimming performance of fasting and fed fish with and without the caudal fin in juveniles of three cyprinid fish species: qingbo (Spinibarbus sinensis, locomotion-priority mode), common carp (Cyprinus carpio, additive mode) and goldfish (Carassius auratus, digestion-priority mode). The critical swimming speed (U(crit)) of fasting qingbo, common carp and goldfish decreased significantly by 49%, 32% and 35% after caudal fin amputation. The maximum tail beat amplitude (TBA(max)) (all three fishes), maximum tail beat frequency (TBF(max)) (only common carp and goldfish) and (or) active metabolic rate (M˙O(2active)) (only common carp) increased significantly after caudal fin amputation. In the control fish, digestion let to a significantly lower U(crit) in goldfish but not in qingbo and common carp, and the M˙O(2active) of digesting common carp was higher than that of fasting fish, suggesting locomotion-priority, additive and digestion-priority metabolic modes in qingbo, common carp and goldfish, respectively. However, after fin amputation, digestion showed no effect on U(crit) in any of the three fishes, and only the digesting common carp showed a higher M˙O(2active) than their fasting counterparts. This result suggested that the metabolic mode of the goldfish changed from the digestion- to the locomotion-priority mode, whereas the metabolic mode of the other two fishes remained the same after fin amputation. The metabolic mode of the common carp showed no change after fin amputation likely due to the high flexibility of the cardio-respiratory capacity of this fish, as indicated by the increased M˙O(2active). Although the metabolic mode remained the same, the feeding metabolism in the fin-amputated qingbo was down-regulated at a lower swimming speed than that of the control group due to the intensified competition between digestion and locomotion. The underlying mechanism for the metabolic mode change in the goldfish is not clear and needs further investigation. However, we speculated that in caudal-fin-intact goldfish, the decreased swimming efficiency, rather than irreducible digestive loading, caused a decreased U(crit) in digesting fish (i.e. false digestion-priority mode), and the metabolic mode should not be judged simply by the relative magnitude of the metabolic rates of fasting and digesting fish.

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

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

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.

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.

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

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

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.