The effect of exercise training on the metabolic interaction between digestion and locomotion in juvenile darkbarbel catfish (Peltebagrus vachelli)

To examine the effects of exercise training on the metabolic interaction between digestion and locomotion in juvenile darkbarbel catfish (Peltebagrus vachelli) (5.58 ± 0.04 g), the postprandial metabolic response, critical swimming speeds (Ucrit) 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% Ucrit for 50 min followed by an exhaustive 10-min chase once daily for 21 days. 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 Ucrit of non-trained fish, while it caused a significantly lower Ucrit (compared to fasting fish) in trained fish (P < 0.05). Training resulted in a significantly higher Ucrit and active VO2 (VO2active) in fasting fish when fish swam at Ucrit. However, training had no effect on either the Ucrit 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.