Lipids, together with proteins, are traditionally considered as primary fuels during aerobic swimming. The effects of dietary fat and carnitine supplements and exercise on the energy metabolism of juvenile fish were investigated. One hundred African catfish (Clarias gariepinus) were fed four isonitrogenous diets containing a fat level of 100 or 190 g kg-1 diet and one of the two levels of carnitine (15 and 1000 mg kg-1). Fish grew from 61 to 162 g in 10 wk. Thereafter, 6 fish per group swam vigorously for 3 h and the results were compared with unexercised groups. Fish receiving 1,000 mg carnitine accumulated 2- to 3-fold more carnitine than fish receiving 15 mg carnitine. Plasma acyl-carnitine level was affected by an interaction between dietary treatment and exercise (P < 0.05). Adenosine triphosphate and phosphocreatine concentrations were higher in the white muscle (WM) of exercised fish fed the high-carnitine supplements, compared with the low-carnitine fed fish (P < 0.05). Adenilate energy charge indexes were higher and ammonia concentrations were lower in WM of fish fed high-carnitine and high-fat diets. Dietary carnitine supplements may be needed in growing fish when dietary lipid level is high. In that case extra dietary carnitine can maintain the body energy reserves at adequate level when fish is exposed to a short-term, exhaustive exercise, a physiologic stress common both in nature and in intensive aquaculture systems.
lipid metabolism; catfish; stress; intensive aquaculture; exhaustive swimming