Characterization and activity of digestive enzymes in different sizes of Nile tilapia (Oreochromis niloticus L.).

The activity of protease, amylase and lipase from the pseudostomach, upper intestine, lower intestine and liver of 5.7, 35.8 and 92.1 g male Nile tilapia (Oreochromis niloticus L.) was determined. Protease activity had an optimal pH of 12, 9 and 9 for the 5.7, 35.8 and 92.1 g fish respectively and the highest specific activity was found in the 35.8 g fish. Amylase activity had an optimal pH of 6, 7 and 2, respectively and the highest specific activity was found in the 92.1 g fish. Lipase activity had an optimal pH of 8, 7 and 8, respectively and the highest specific activity was found in the 35.8 g fish. In all sizes of tilapia, amylase activity was significantly higher in the liver than other organs (P<0.01). Protease and lipase activity in the lower and upper intestine respectively of the 5.7 and 35.8 g fish were significantly higher than in other organs (P<0.01). This study indicated that different sizes of fish had different levels of enzymatic activities. Middle-sized fish appeared to have the highest specific activity of protease and lipase, while the large fish had the highest specific activity of amylase. These results will be used as a basis for suitable feed formulation for different sizes of Nile tilapia so that optimum nutritional values and cost-effectiveness can be achieved.