Effects of temperature and digestion on the swimming performance of juvenile Chinese bream

Abstract

Fish that are active foragers usually perform routine activities while digesting their food; thus, postprandial swimming capacity might be ecologically important. To test whether digestion affected swimming performance in an active forager and whether the possible effects varied with temperature, we investigated the critical swimming speed (Ucrit) and the resting and active metabolic rate (MO2) of fasted and fed juvenile Chinese bream Parabramis pekinensis after 30 d exposure to 3 temperatures (15, 20, and 25°C). In fasted fish, Ucrit, resting and active MO2 all increased with temperature. Digestion elicited a significant increase in MO2, which was enhanced at higher temperatures. Compared to fasted fish, fed fish exhibited significantly lower Ucrit in both the 25 and 20°C groups, whereas no significant difference in Ucrit was observed between fasted and fed fish in the 15°C group. Furthermore, digestion resulted in a significantly higher active MO2 in the 15°C group, whereas no significant difference in active MO2 was observed between fasted and fed fish in the 20 and 25°C groups. This suggests that the bream adopted an additive metabolic mode, i.e. digestion and swimming were performed independently at low temperatures, but shifted to a digestion-priority mode at higher temperatures due to a shortage of oxygen resulting from an increased digestive and locomotive oxygen demand. The present study contradicted our hypothesis that an active cyprinid with high swimming performance would give priority to locomotion when the oxygen supply was insufficient to meet the metabolic demands of both digestion and swimming.