Growth Responses, Tissue Composition, and Liver Enzyme Changes in Juvenile Sunshine Bass,Morone chrysops×M. saxatilis, Associated with Dietary Protein and Lipid Level

Four isocaloric, semi-purified diets containing low (30%) or high (50%) protein with either 12 or 18% lipid were fed at 4% of body weight to juvenile sunshine bass, Morone chrysops ×M. saxatilis, for 12 weeks (initial weight = 3.4 g). Fish fed the high protein diets gained significantly more weight and had better feed conversions than fish fed low protein diets. There were no significant differences in muscle or total body moisture and lipid or in intraperitoneal fat associated with either dietary protein or lipid levels. However, muscle protein and liver lipid increased significantly at high protein and lipid levels, respectively. Liver alanine amino transferase activities increased significantly at the high dietary protein and lipid levels, indicating that excess dietary protein was being used for non-protein processes. Fruc-tose-1,6-diphosphatase and pyruvate kinase activities indicated that excess dietary protein was not being used to synthesize glucose or glyco-gen. Malic enzyme activities decreased in response to increased dietary lipid, but did not respond to changes in dietary protein, indicating that excess protein was not being used for lipid synthesis. It is hypothesized the excess dietary protein is used for energy production.