The effects of dietary protein level on growth perfonnance and resistnce to Aeromonas hydrophila of Nile tilapia (Oreochromis niloticus) were determined in glass aquaria. Apparently healthy specinens of the Nile tilapia (31 g initial body weight) were used in a feeding experiment with five dietary protein levels. Three random groups of ten fish per glass
aquaria were maintained at each treatment The diets were formulated from commercial ingredients to contain the five dietary crude ltotein levels (14, 20, 26, 32 and 38%) and 245 kcal metabolizabte energy /100g using soybean meal and fishmeal in a fixed ratio (2:1). Fish were fed twice daily for 12 weeks. After the feeding experiment, five fish were per treatment were randomly picked up for intra peritoneal injection with 0.1 ml of formalin inactivated hot-strain of isolated Aeromonas hydrophila. Two weeks later fish were intramuscularly challenged with 0.1 ml /fish containing approximately 9x 10 7 cells of viable homologous virulent strain of A hydrophila. Challenged fish from each treatment were kept under
observation for 7 days post-challenge. Results revealed that increasing dietary protein level had no significant effect on the final body weight. Energy retention (ER) of fish fed 26% dietary protein level was higher (P<0.05) than those received 32 and 38%. Also feed conversiosj ratio (FCR) improved with increasing dietary protein level up to26%. But protein
efficiency ratio (PER) and protein productive value (PPV) decreased significantly (P<0.05) with increasing dietary protein level. No significant differences among the feeding treatments were occurred in survival rate. The intramuscularly challenged fish with virulent strain of I A. hydrophila were showed hemorrhage ulceration at the inoculation sites. Fish that maintained at 26% dietary protein level obtained the higher level of antibody protection. Low mortality and morbidity was observed on fish maintained at 26% dietary protein level. Generally, it can be concluded that even if the low protein levels gave the same growth performance, we can recommend 26% dietary protein level for the best growth and resistance to A. hydrophilic infection.