SUMMARYThe objective of this study was to determine whether acclimation to hypoxia and sustained exercise would increase hypoxia tolerance (as indicated by a decrease in critical oxygen tension, P crit ) and swimming performance in goldfish (Carassius auratus), and to investigate the relationship between changes in performance and gill remodelling and tissue metabolic capacity. Goldfish were acclimated to either hypoxia (48h at 0.3mg O 2 l ) and compared with values from control fish. Acclimation to both hypoxia and sustained exercise improved hypoxia tolerance (P crit was reduced by 49% and 39%, respectively), which was associated with an increase in lamellar surface area (71% and 43%, respectively) and an increase in blood [Hb] (26% in both groups). Exercise acclimation also resulted in a decrease in routine M O2 (M O2,rout ). Acclimation to both hypoxia and sustained exercise resulted in a significant increase in U crit in hypoxia (18% and 17%, respectively), which was associated with an increase in maximal O 2 consumption rate at U crit (M O2,active ; 35% and 39%, respectively). While hypoxia acclimation resulted in an increase in U crit in normoxia, acclimation to sustained exercise did not improve subsequent swimming performance in normoxia. This lack of improvement was possibly due to depleted oxidizable substrates during exercise acclimation.
SUMMARYTo 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 (U crit ), lowest maintenance metabolism (V O2rest ) and lowest maximum locomotory metabolism (V O2max ). However, the southern catfish had the highest feeding level and maximum feeding metabolism (V O2peak ) and the greatest decrease in U crit 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 U crit 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 V O2max after feeding) guarantees a small decrease in U crit 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.
To investigate the effects of exhaustive chasing training and detraining on the swimming performance of juvenile darkbarbel catfish (Peltebagrus vachelli Richardson), we performed exhaustive chasing training daily for 14 days and subsequently detrained fish for 7 days. Chasing training resulted in significant increases in critical swimming speed (U (crit)), post-chasing peak oxygen consumption rate (VO(2 peak)), and heart and gill indexes compared with non-trained controls. Both resting oxygen consumption (VO(2 rest)) and excess post-chasing VO(2) (EPOC) were unaffected by exhaustive chasing training. Fish that underwent chasing training had lower levels of whole-body lipid content and reduced food intake and growth compared with non-trained control fish; however, condition factor was not affected by chasing training. Seven days of detraining reversed the effects of exhaustive chasing training. Overall, these data suggested that short-term exhaustive chasing training improves aerobic swimming capacity in darkbarbel catfish, but the training effects are reversible over a short period of time.
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