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Metabolic rates vary widely within species, but little is known about how variation in the 'floor' [i.e. standard metabolic rate (SMR) in ectotherms] and 'ceiling' [maximum metabolic rate (MMR)] for an individual's aerobic scope (AS) are linked with digestive and locomotor function. Any links among metabolic traits and aspects of physiological performance may also be modulated by fluctuations in food availability. This study followed changes in SMR, MMR, and digestive and locomotor capacity in southern catfish ( Silurus meridionalis ) throughout 15 days of food deprivation and 15 days of refeeding. Individuals downregulated SMR during food deprivation and showed only a 10% body mass decrease during this time. Whereas critical swim speed ( U crit ) was robust to food deprivation, digestive function decreased after fasting with a reduced peak oxygen uptake during specific dynamic action (SDA) and prolonged SDA duration. During refeeding, individuals displayed rapid growth and digestive function recovered to pre-fasting levels. However, refed fish showed a lower U crit than would be expected for their increased body length and in comparison to measures at the start of the study. Reduced swimming ability may be a consequence of compensatory growth: growth rate was negatively correlated with changes in U crit during refeeding. Southern catfish downregulate digestive function to reduce energy expenditure during food deprivation, but regain digestive capacity during refeeding, potentially at the cost of decreased swimming performance. The plasticity of maintenance requirements suggests that SMR is a key fitness trait for in this ambush predator. Shifts in trait correlations with food availability suggest that the potential for correlated selection may depend on context., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)

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., (Copyright © 2016 Elsevier Inc. All rights reserved.)

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., (Copyright © 2013 Elsevier Inc. All rights reserved.)

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., (Copyright © 2012 Elsevier Inc. All rights reserved.)

To test whether the effects of water oxygen concentration ([O(2)]) on the metabolic interaction between locomotion and digestion differ between fish species with different locomotive and digestive behaviours in normoxia, we investigated the swimming performance of fasted and fed fish at water [O(2)] of 1, 2 and 8 (normoxia) mg L(-1) (2.5, 5 and 20 kPa) at 25°C in three juvenile Cyprinidae fish species: goldfish (Carassius auratus), common carp (Cyprinus carpio) and qingbo (Spinibarbus sinensis). Digestion, taxon and water [O(2)] all had significant effects on the pre-exercise oxygen consumption rate [Formula: see text] and the swimming performance (P < 0.05). Among the three fishes, qingbo showed the highest swimming performance and the lowest feeding [Formula: see text] at the saturated water [O(2)], and its active oxygen consumption rate [Formula: see text] and critical swimming speed (U (crit)) decreased the most with decreases in water [O(2)]. Qingbo exhibited a locomotion-priority metabolic mode at all three water [O(2)]. Digestion was sacrificed to locomotion in a postprandial swimming situation, but fed qingbo could not maintain their U (crit) at water [O(2)] of 2 and 1 mg L(-1). Goldfish showed the lowest swimming performance and the highest feeding [Formula: see text] at the saturated water [O(2)]. They exhibited a digestion-priority metabolic mode at high water [O(2)]. However, with a decrease in water [O(2)], the feeding [Formula: see text] decreased more acutely than the respiratory capacity; thus, digestion and locomotion performed independently in a postprandial swimming situation (i.e., an additive metabolic mode) at a water [O(2)] of 1 mg L(-1). The common carp showed moderate and balanced swimming performance and feeding [Formula: see text] at the saturated water [O(2)], and exhibited an additive metabolic mode at all 3 water [O(2)], because digestion, swimming and respiratory capacities decreased in parallel with the decrease in water [O(2)].

To test whether the effects of temperature on the metabolic mode changed among different fish species, we investigated the specific dynamic action (SDA) and swimming performance of fasting and fed fish at 15 and 25°C in three juvenile Cyprinidae fish species: goldfish (Carassius auratus), common carp (Cyprinus carpio) and qingbo (Spinibarbus sinensis). Both taxon and temperature had significant effects on the resting oxygen consumption rate (M˙O(rest)), SDA and swimming performance (p<0.05). In addition, the effect of temperature differed significantly among the different species (interaction effect, p<0.05). Under the low temperature condition, digestion had no effect on either critical swimming speed (U(crit)) or the active MO(2) (MO(active)) for all fish species (additive metabolic mode). When the temperature was increased from 15 to 25°C, the metabolic scope (MS) for digestion increased approximately 182, 49 and 17%, and the MS for locomotion increased approximately 129, 58 and 138% in goldfish, common carp and qingbo, respectively. The total metabolic demands for both digestion and locomotion (i.e., the sum of digestive MS and locomotive MS) increased approximately 143, 56 and 112% in goldfish, common carp and qingbo, respectively. The total MS for both digestion and locomotion (the difference between MO(active) in fed fish and MO(rest) in fasting fish) increased approximately 106, 58 and 78% in goldfish, common carp and qingbo, respectively. Thus, the MS for locomotion in fed goldfish decreased due to the large increase in digestive function at the high temperature, and the U(crit) of fed goldfish decreased by 11% compared to that of fasting fish (p<0.05) (digestion-priory metabolic mode). The metabolic mode of qingbo changed to locomotion-priority mode, as illustrated by the large increase in locomotive MS in response to the increase in temperature. In the common carp, temperature had no effect on metabolic mode as illustrated by the parallel increases in cardio-respiratory capacity and metabolic capacity of digestive and locomotive organs. A discussion on the changes in metabolic mode in response to temperature and its possible relationship with the metabolic characteristics of a given fish species was also documented in this paper., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The southern catfish exhibits the largest decrease in critical swimming speeds (U(crit)) during digestion among the fish species that have been investigated. To test whether the maximum metabolic capacity of the southern catfish was improved after exercise training to alleviate the competitive interaction between digestion and swimming, we measured postprandial metabolic responses, U(crit) and oxygen consumption rates (MO(2)) during swimming in both fasting and digesting fish. Twenty-one days of training (50 min swimming at 60% U(crit) followed by 10 min chasing) did not produce significant differences in resting MO(2) (MO(2rest)) or postprandial peak MO(2) (MO(2peak)). However, it did result in a significant decrease in energy expenditure during digestion. Feeding caused a significant decrease in U(crit) and an increase in active MO(2) (MO(2active)), whereas training caused a significant increase in U(crit) but no significant change in MO(2active). Neither digestion nor training had a significant effect on metabolic scope (MO(2active)-MO(2rest)). Training had no interactive effect on postprandial changes in any measured variable, so we conclude that training did not alleviate the competitive interaction between digestion and swimming. Our results suggest that: (1) the metabolic capacity of nontrained fish cannot support the metabolic demands of both digestion and locomotion simultaneously, and swimming metabolism, therefore, is sacrificed to sustain digestion when feeding and locomotion are combined (digestion-prioritization mode); (2) the metabolic capacity and metabolic mode of competition did not change after training, but trained fish did exhibit improved swimming performance, possibly due to their increased rate of O(2) extraction.

To investigate the effect of dissolved oxygen level ([O(2)]) on maintenance metabolism, feeding metabolism, aerobic swimming performance and their metabolic interaction in juvenile southern catfish (Silurus meridionalis Chen), we measured the following: (1) the resting oxygen consumption rate (MO(2rest)) over a range of water [O(2)] and from this we calculated the critical oxygen tension (P(crit)) of fasting fish; (2) the postprandial MO(2) response (10% body mass meal size) at water [O(2)] of 1, 2, 4 and 8mgO(2)L(-1); and (3) the swimming performance of fasting and digesting fish at water [O(2)] of 1, 2, 4 and 8mgO(2)L(-1) at 25 degrees C. The MO(2rest) remained constant over a broad range of water [O(2)] but then dropped markedly upon reaching the P(crit) (16.4% saturation). Hypoxic groups presented lower peak postprandial MO(2) (MO(2peak)) (1mgO(2)L(-1) group), larger energy expenditure and longer digestive process (both 1 and 2mgO(2)L(-1)) than those of normoxic groups. Both critical swimming speed (U(crit)) and the active metabolic rate (MO(2active)) of fasting fish remained unchanged over a decrease in water [O(2)] from 8 to 4mgO(2)L(-1) and then decreased significantly with further decreases in water [O(2)]. These parameters in fed fish showed a pronounced decrease as water [O(2)] decreased from 8 to 1mgO(2)L(-1). Feeding caused a significantly lower U(crit) in the 2mgO(2)L(-1) water [O(2)] group, a significantly higher MO(2active) in both the 2 and 8mgL(-1) water [O(2)] groups and a significantly higher metabolic scope (MO(2active)-MO(2rest)) in both the 2 and 4mgO(2)L(-1) water [O(2)] groups compared to fasting fish. The MO(2) increased greatly with swimming speed in the higher water [O(2)] groups, whereas it leveled off as swimming speeds approached the U(crit) in the lower water [O(2)] groups. Within all water [O(2)] groups, feeding caused a higher MO(2) compared to fasting fish when fish swam at the same speeds, except in the 1mgO(2)L(-1) group. This finding showed that the critical water [O(2)] for maintenance of metabolism, digestion, swimming and postprandial swimming increased sequentially due to the increasing O(2) demand, which challenges respiratory capacity. With the administration of the medium-sized meal that was used in this study, the metabolic mode of juvenile southern catfish changed from an additive mode during normoxia to a digestion-priority mode under moderate hypoxia and to locomotion-priority mode under hypoxia., (Copyright 2010 Elsevier Inc. All rights reserved.)

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).

The effects of meal size on the postprandial metabolic response and of digestion on the post-exercise metabolic recovery process were investigated in juvenile black carp (Mylopharyngodon piceus). Experimental fish were forcedly fed with compound feed (meal sizes: 0.5%, 1% and 2% body weight). Then, the postprandial oxygen consumption rate and excess post-exercise oxygen consumption (EPOC) of the experimental fish were measured. Both the duration and the peak of oxygen consumption rate (PMR) increased with increasing meal size. The peak post-exercise metabolic rate of digesting fish were significantly higher, whereas EPOC magnitude and its duration were significantly smaller or (shorter) than those in the fasting fish. It is suggested that (1) this fish fulfills the increased energy demand during the digestive process by increasing PMR and by prolonging SDA duration with increasing meal size and (2) digesting fish might decrease their anaerobic exhaustive activity but increase the post-exercise recovery capacity. [ABSTRACT FROM AUTHOR]

Exercise and aerobic scope in fishes have attracted scientists' attention for several decades. While it has been suggested that aerobic scope may limit behavioral expression and tolerance to environmental stressors in fishes, the exact importance of aerobic scope in an ecological context remains poorly understood. In this review, we examine the ecological relevance of aerobic scope by reconsidering and reanalyzing the existing literature on Chinese freshwater fishes across a wide-range of habitats and lifestyles. The available evidence suggests that natural selection in fast-flowing aquatic habitats may favor species with a high aerobic scope and anaerobic capacity for locomotion, whereas in relatively slow-flowing habitats, hypoxia tolerance may be favored at the cost of reduced locomotor capacity. In addition, while physical activity can usually cause fishes from fast-flowing habitats to reach their aerobic metabolic ceiling (i.e., maximum metabolic rate), possibly due to selection pressure on locomotion, most species from slow-flowing habitats can only reach their metabolic ceiling during digestion, either alone or in combination with physical activity. Overall, we suggest that fish exhibit a continuum of metabolic types, from a 'visceral metabolic type' with a higher digestive performance to a 'locomotion metabolic type' which appears to have reduced capacity for digestion but enhanced locomotor performance. Generally, locomotor-type species can either satisfy the demands of their high swimming capacity with a high oxygen uptake capacity or sacrifice digestion while swimming. In contrast, most visceral-type species show a pronounced decrease in swimming performance while digesting, probably owing to conflicts within their aerobic scope. In conclusion, the ecological relevance of aerobic scope and the consequent effects on other physiological functions are closely related to habitat and the lifestyle of a given species. These results suggest that swimming performance, digestion and hypoxia tolerance might coevolve due to dependence on metabolic traits such as aerobic scope. [Display omitted] • Selection favors fishes with high metabolic capacities but poor hypoxia tolerance in fast-flow habitats. • Exercise can elicit the metabolic ceiling of fishes in fast-flow habitats, whereas most species in slow-flow habitats cannot. • Fish exhibit a continuum of metabolic types, i.e., visceral metabolic type to locomotion metabolic type. • The ecological relevance of aerobic scopeis related to habitat condition and the particular lifestyle of a given species. • The swimming performance, digestion and hypoxia tolerance might coevolve due to dependence on metabolic traits. [ABSTRACT FROM AUTHOR]

Empirical studies suggest that individuals with a high resting metabolic rate (RMR) are at an advantage under favourable conditions because they digest food rapidly and exhibit a greater growth potential. However, we hypothesised that high-RMR individuals have less energy available for digestion under hypoxia than they do under normoxia due to their relatively high maintenance cost. To test this hypothesis, we measured the RMR and postprandial metabolic responses of juvenile southern catfish,Silurus meridionalis, under normoxia and moderate hypoxia. The results provided the first evidence that (1) both the RMR and postprandial metabolic rate showed repeatability across different water [O2] conditions and (2) the correlation between the RMR and postprandial metabolic traits differs with changes in environmental factors (water [O2]). These findings suggested that the digestive advantage of individual southern catfish with a high RMR is impaired under hypoxia. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the effect of fasting on maintenance metabolism, feeding metabolism and aerobic swimming performance as well as their metabolic interactions in juvenile southern catfish, we measured the following: (1) the postprandial oxygen consumption () response (16% body mass meal size) after 0 (control), 1, 2 and 4weeks of fasting and (2) the swimming performance of non-digesting and digesting fish after either 0, 1, 2 or 4weeks of fasting. The fasting groups displayed with lower resting ( rest), lower peak postprandial ( peak), larger energy expenditures and longer digestive processes than those of the control groups. The critical swimming speed (U crit), the active ( active) and the metabolic scope ( active - rest, MS) of both non-digesting and digesting fish all decreased progressively after 1, 2 and 4weeks of fasting, with those of non-digesting fish decreased more acutely than digesting fish (P <0.05). Digesting fish displayed with a 14%, 23%, 27% and 71% significantly higher active than that of non-digesting fish in the 0-, 1-, 2- and 4-week fasting groups. Digestion only caused a significantly lower U crit and MS in both the 0- and 1-week fasting groups (P <0.05). The increased greatly with the swimming speed, and digestion caused a higher when compared to that of the fasting fish in any groups. The of fish in the 4-week fasting group was significantly lower than that of other groups when the swimming speed was the same. In conclusion, both digestive and locomotive functions were down-regulated during fasting. In the 0- and 1-week fasting groups, the decreased MS for swimming during digestion caused a lower U crit (i.e., a digestion priority model). However, because the active of digesting fish decreased much more slowly than that of fasting fish, the MS of the 2- and 4-week fasting groups did not change during digestion, and the fish could handle both physiological activities independently (i.e., an additive model). [Copyright &y& Elsevier]

Abstract: The impact of feeding (fed to satiation, 13.85% body mass) on excess post-exercise oxygen consumption (EPOC, chasing for 2.5 min) was investigated in juvenile southern catfish (Silurus meridionalis Chen) (38.62–57.55 g) at 25. Cutlets of freshly killed loach species without viscera, head and tail were used as the test meal, and oxygen consumption (VO2) was adjusted to a standard body mass of 1 kg using a mass exponent of 0.75. Resting VO2 increased significantly above fasting levels (49.89 versus 148.25 mg O2 h− 1) in 12 h postprandial catfish. VO2 and ventilation frequency (V f) both increased immediately after exhaustive exercise and slowly returned to pre-exercise values in all experimental groups. The times taken for post-exercise VO2 to return to the pre-exercise value were 20, 25 and 30 min in 12 h, 60 h and 120 h postprandial catfish, respectively. Peak VO2 levels were 257.36±6.06, 219.32±6.32 and 200.91±5.50 mg O2 h−1 in 12 h, 60 h and 120 h postprandial catfish and EPOC values were 13.85±4.50, 27.24±3.15 and 41.91±3.02 mg O2 in 12 h, 60 h and 120 h postprandial southern catfish, respectively. There were significant differences in both EPOC and peak VO2 during the post-exercise recovery process among three experimental groups (p <0.05). These results showed that: (1) neither digestive nor exhaustive exercise could elicit maximal VO2 in southern catfish, (2) both the digestive process and exercise (also the post-exercise recovery process) were curtailed under postprandial exercise, (3) the change of V f was smaller than that of VO2 during the exhaustive exercise recovery process, (4) for a similar increment in VO2, the change in V f was larger during the post-exercise process than during the digestive process. [Copyright &y& Elsevier]

The acclimation rate of physiological functions that bear fitness costs under a changing environment is key to making predictions for fish, yet this has seldom been investigated. This study aimed to test whether there were different responses when different physiological functions reached steady states and to determine possible relationships with metabolic constraints during temperature changes in fish. Qingbo ( Spinibarbus sinensis ), a common cyprinid in southern China, was first pre-acclimated at either high (25 °C) or low (15 °C) temperature for eight weeks and assumed to be at thermal equilibrium. Then, the temperature was reversed, that is, the temperature was decreased from 25 °C to 15 °C in one group, defined as the cooling group, whereas the temperature of the other group was increased from 15 °C to 25 °C, defined as the warming group. The thermal tolerance, swimming performance and feeding metabolism were measured before temperature reversal as well as 1, 2, 4 and 8 weeks. The growth performance was also measured after the temperature reversal. Typical thermal compensation was suggested by a stronger heat tolerance, faster swimming speed and higher postprandial metabolic response in those acclimated at 25 °C than in those acclimated at 15 °C before temperature reversal. Cold tolerance suggested by the critical minimal temperature (CTmin) of the cooling group reached a thermal steady state within one week, whereas the adjustment of heat tolerance to the temperature increase indicated by the critical maximum temperature (CTmax) was much slower, reaching a steady state two weeks after the temperature reversal. The high flexibility of the standard metabolic rate as well as the postprandial metabolism and relatively lower feeding metabolism demonstrated that there were negligible effects at the aerobic scope for other physiological functions during digestion in qingbo, even during the temperature acclimation period. However, there was a slower adjustment of the swimming performance with the temperature decrease, which parallels the change of metabolic capacity. Furthermore, both the cooling and warming treatments had negative effects on growth performance, with the former mainly occurring through extra energy expenditure, whereas the latter mainly occurred through decreased feeding. It suggested that the slow adjustment of heat tolerance after the temperature increase compared to that of cold tolerance might be a challenge for cyprinids distributed in southern China. Furthermore, the decreased metabolic scope and hence swimming performance after the temperature decrease might have a fitness cost in qingbo and possibly other cyprinids in China. [ABSTRACT FROM AUTHOR]

Abstract: To examine the effects of exercise training on the metabolic interaction between digestion and locomotion in juvenile darkbarbel catfish (Peltebagrus vachelli) (5.58±0.04g), the postprandial metabolic response, critical swimming speeds (U crit) and oxygen consumption rates (VO2) during swimming were measured on fish held at a constant temperature (25°C). Fish were fed a diet of cutlets of freshly killed loach. Fish in the trained group were forced to swim at 60% U crit for 50min followed by an exhaustive 10-min chase once daily for 21days. Exercise training did not produce significant differences in resting VO2 (VO2rest) and postprandial peak VO2 (VO2peak) compared to the non-trained groups. However, exercise training elicited a significant decrease in both the duration and energy expenditure of digestion when fed with similar food (P <0.05). Feeding had no significant effect on U crit of non-trained fish, while it caused a significantly lower U crit (compared to fasting fish) in trained fish (P <0.05). Training resulted in a significantly higher U crit and active VO2 (VO2active) in fasting fish when fish swam at U crit. However, training had no effect on either the U crit or VO2active of post-feeding fish. Our results suggest that: (1) the central cardio-respiratory systems of non-trained darkbarbel catfish can support the oxygen demands of both digestion and the locomotion simultaneously; (2) the metabolic mode of competition in darkbarbel catfish is flexible; it changed from an additive model to a digestion-priority model after exercise training; (3) training may be accounted for cardio-respiratory capacity increase and following improvement of swimming performance during fasting in darkbarbel catfish, although, the swimming capacity was sacrificed to digestion in the situation of postprandial locomotion. [Copyright &y& Elsevier]

Abstract: To test whether the effects of feeding on swimming performance vary with acclimation temperature in juvenile southern catfish (Silurus meridionalis), we investigated the specific dynamic action (SDA) and swimming performance of fasting and feeding fish at acclimation temperatures of 15, 21, 27, and 33°C. Feeding had no effect on the critical swimming speeding (U crit) of fish acclimated at 15°C (p =0.66), whereas it elicited a 12.04, 18.70, and 20.98% decrease in U crit for fish acclimated at 21, 27 and 33°C, respectively (p <0.05). Both the maximal postprandial oxygen consumption rate (VO2peak) and the active metabolic rate (VO2active, maximal aerobic sustainable metabolic rate of fasting fish) increased significantly with temperature (p <0.05). The postprandial maximum oxygen consumption rates during swimming (VO2max) were higher than the VO2active of fasting fish at all temperature groups (p <0.05). The VO2max increased with increasing temperature, but the relative residual metabolic scope (VO2max− VO2peak) during swimming decreased with increasing in temperature. The present study showed that the impairment of postprandial swimming performance increased with increasing temperature due to the unparalleled changes in the catfish''s central cardio-respiratory, peripheral digestive and locomotory capacities. The different metabolic strategies of juvenile southern catfish at different temperatures may relate to changes in oxygen demand, imbalances in ion fluxes and dissolved oxygen levels with changes in temperature. [Copyright &y& Elsevier]