Postprandial intestinal blood flow, metabolic rates, and exercise in Chinook Salmon (Oncorhynchus tshawytscha)

Following a relatively large meal (2% body mass of dry pellets), intestinal blood flow in chinook salmon (Oncorhynchus tshawytscha) increased significantly, up to 81%, between 14 and 29 h postprandially. Also, 15 h postprandially, oxygen consumption (Mo-2) was elevated by 128% compared with a measurement of routine Mo-2 made after 1 wk of fasting. The post prandial increase in Mo-2 (the heat increment) was 33 mu mol O-2 min(-1) kg(-1). Because intestinal blood flow is known to decrease during swimming activity in fish, we therefore tested the hypothesis that swimming fish would have to make a trade-off between maximum swimming activity and digestive activity by comparing the swimming performance and metabolic rates of fed and fasted chinook salmon. As expected, Mo-2 increased exponentially with swimming velocity in both fed and fasted fish. Moreover, the heat increment was irreducible during swimming, such that Mo-2 remained approximately 39 mu mol O-2 min(-1) kg(-1) higher in fed fish than in fasted fish at all comparable swimming speeds. However, maximum Mo-2 was unaffected by feeding and was identical in both fed and fasted fish (similar to 250 mu mol O-2 min(-1) kg(-1)), and, as a result, the critical swimming speed (U-crit) was 9% lower in the fed fish. Three days after the fish were fed and digestion was completed, Mo-2 and U-crit were not significantly different from those measured in fasted fish. The ability of salmonids to maintain feeding metabolism during prolonged swimming performance is discussed, and it is suggested that reduced swimming performance may be due to postprandial sparing of intestinal blood to support digestion, thereby limiting the allocation of blood flow to locomotory muscles.