Aone way experiment was conducted with Nile tilapia, Oreochromis niloticus, using restricted feeding with 4280, 4370, 4520, 4660, 4800 and 4860 Kcal / kg diet of dietary energy concentration with isonitrogenous contant (33 % crude
protein). Diets were fed to triplicate random groups of 30 fry for 84 day in glass aquaria. At a constant dietary protein level, weight gain and protein efficiency ratio increased with increasing dietary energy level. The body fat content of the
experimental fish increased with the increaseing of dietary energy level. Fish fed diets E and F (4800 and 4860 Kcal/kg) had significantly higher fat content than those of fish fed all other diets. Protein productive value (PPV) of Nile tilapia given diet containing 330 g protein and 4800 kcal /kg diet was significantly higher than those of fish fed all other dietary energy levels. Dietary energy levels correlated positively with weight gain, body length, body weight, SGR and total feed intake, (r = 0.91, 0.91, 0.92, 0.92, 0.92) and negatively with feed conversion ratio (FCR) and PER (r = - 0.90 and - 0.86). The apparent digestibility coefficients for dry matter, protein and lipid were significantly affected by dietary energy levels while, digestibility of energy was not significantly affected by energy levels. The energy budget at the restricted
feeding was 100 IE = 14.9 FE + 5.79 (ZE + UE) + 63.37 HE + 15.94 RE, where IE, FE, (ZE + UE), HE and RE represented gross energy intake, fecal energy, excretory energy loss, heat production and growth energy, respectively. It can be suggesed that dietary energy of 4800 Kcal GE / kg or 4000 Kcal DE / kg diet with a constant dietary protein of 33.0 % was superior to high growth rate and best food utilization of juvenile Nile tilapia under the conditions of this study.