Digestive enzymes present in Pacific threadfin Polydactylus sexfilis (Bloch and Schneider 1801) and bluefin trevally Caranx melampygus (Cuvier 1833)

摘要

Pacific threadfin Polydactylus sexfilis (Bloch and Schneider 1801) and bluefin trevally Caranx melampygus (Cuvier 1833) are warmwater marine finfish currently under development for aquaculture in the Pacific. Differences in specific activities of digestive enzymes extracted from the stomach and mid-gut were compared to gain insight into their feeding habits in the wild and to understand their nutritional needs. Adult fish were maintained in captivity and fed a commercial pelleted feed. Serine protease measured in all tissues was at least 20 times higher in threadfin than in trevally. Aspartic proteases were the major digestive enzymes found in trevally. There was a 34-fold increase in collagenase activity in the intestine of threadfin from the prefed to the fed state. Chitinase activity was found in the stomach, pylorus and intestine of both species. However, specific activity in pylorus and intestine of threadfin increased 2.75 and 4 times, respectively, but showed little change in trevally. Amlyases were found only in trevally. Increase in lipase specific activity in the gut of trevally was higher than that for threadfin. The results indicated that the two species have diverse digestive capabilities. This appears to be consistent with their feeding habits in nature. Threadfin are more adapted to a wider range of food protein sources than trevally, but appear to be less well adapted than trevally to using complex carbohydrates. These observations may provide a basis for practical diet formulations for these two species.