Growth performance, oxidative stress indices and hepatic carbohydrate metabolic enzymes activities of juvenile Nile tilapia, Oreochromis niloticus L., in response to dietary starch to protein ratios

The effect of various dietary starch to proteins ratios (STA/P) on growth performance, oxidative status and liver enzyme activities involved in intermediary metabolism in juvenile Nile tilapia was evaluated. Four isocaloric-practical diets (12.73MJkg(-1) digestible energy) with increasing STA/CP ratios were formulated. These were designated D-0 (344g crude protein (CP) and 163.5g starch (STA) kg(-1)), D-1 (310g CP and 243g STAkg(-1)), D-2 (258g CP and 322g STA kg(-1)) and D-3 (214g CP and 401g STA kg(-1)). Each diet was fed to triplicate groups of 60 fish (2.7g) for 45days. Compared with the control diet (D-0), significantly (P<0.05) depressed growth and feed efficiency were observed only in the groups fed on diet D-3. The activities of hepatic enzymes involved in glycolysis and lipogenesis pathways were significantly enhanced in groups fed on diet D-3 compared with other diets. A significant (P<0.05) increase in catalase activity was detected only in groups fed on diet D-3. Similarly, a significant (P<0.05) enhancement in superoxyde dismutase, glutathione S-transferases and glutathione peroxidise was observed in groups fed on diets D-2 and D-3 compared with other diets. Results demonstrate the ability of juvenile Nile tilapia to spare protein by dietary carbohydrate.