Title: EFFECTS OF STOCKING DENSITY AND PROTEIN LEVEL IN DIET ON GROWTH PERFORMANCE, SURVIVAL RATE AND FEED EFFICIENCY OF NILE TILAPIA (OREOCHROMIS NILOTICUS L.) FRY MONOSEX DURING THE NURSERY PERIOD.
Abstract: T he effects of stocking density and dietary protein levels on growth performance, larval survival and feed utilization efficiency of Nile tilapia (O.niloticus L.) fiy monosex (0.014 g average initial body weight) were investigated in a single-stage nursery-rearing system using 1389 and 2778 hatchlings/ m 3 as stocking densities within each density 29.71, 34.43 and 39.11% dietary protein levels.Twelve fiberglass tanks (180 liter volume for each) on a flow-through system (100%/day)were used to represent the two stocking densities and the three protein levels in replicates.The dietary treatments were fed 7 days/week (twice daily) at a rate of 15% of the total biomass during the 1 st 45-days then reduced to 10% of total biomass from days 46 to 75, after that it was reduced to 5% of total biomass till the end of the experiment (105 days).The results revealed that there was significant increase (P< 0,01) in growth rate with decreasing stocking density and increasing dietary protein level during all experimental periods.The same trend was also observed for mean body weight (g), specific growth rate (SGR%/day), condition factor (k) and survival rate (SR %).The best final mean body weight (g), SGR, K and (SR %) were recorded in groups of fish stocked in 1389 hatchlings /m 3 and fed on the diet containing 39.11% CP) (T3SR1).Feed conversion ratio (FCR) was significantly (P< 0.01) decreased (improved) in T3SR1 (Lower stocking density with higher dietary protein level) group compared to the other groups.Improvement in FCR was achieved when dietary protein increased, while increasing stocking density increased (not improved) FCR (P< 0.01).On the contrary, protein 70 Ramadan A. Abou-Seif efficiency ratio (PER) was negatively correlated with dietary protein level and stocking density.The highest net return was achieved with T3SR1 (lower stocking density with higher dietary protein) followed in a descending order by fish of T 2 SR 2 (higher stocking density with medium dietary protein) and T3SR2 (higher stocking density with higher dietary protein).The lowest net return was recorded by fish of T]SR 2 (higher stocking density with lowers dietary protein).Results of this study revealed that fish reared at low stocking density (1389 hatchlings/m 3 ) and fed high dietary protein level (39.11%)T3SR] group may be advisable in a single-stage nursing for production of adequate quality seeds of Nile tilapia monosex in short time with lowest mortality in order to be available as healthy fry at the beginning of the culture season for fish farmers.