Gut blood flow in fish during exercise and severe hypercapnia

This paper reviews the effects of exercise and hypercapnia on blood flow to the splanchnic circulation. Brief struggling behaviours are known to decre ase blood flow to the gut (GBF). Likewise, prolonged swimming in unfed fish has been shown to reduce GBF in proportion to the increased oxygen uptake. Therefore, the normal postprandial increase in GBF theoretically should be impaired whenever fish are active. However, indirect evidence suggests tha t GBF is spared to some degree when fed fish swim continuously but at a cos t (10-15%) to their critical swimming speed. Severe respiratory acidosis ca n be created by the new intensive aquaculture settings that use oxygen inje ction into re-circulated water. The only study so far to examine the effect s of severe hypercapnia on GBF and its regulation showed that routine GBF a nd a-adrenergic control of GBF remained normal in unfed white sturgeon (Aci penser transmontanus). However, severe hypercapnia produced a hyperactive s tate and increased sensitivity of GBF to struggling. As a result, routine G BF was maintained for a short period of time. Thus, environmental changes s uch as severe hypercapnia can indirectly impact GBF through altered struggl ing behaviour, but the implications of the overall reduction in GBF to food assimilation have yet to be established. (C) 2001 Elsevier Science Inc. Al l rights reserved.