Intraspecific variation of Oreochromis niloticus (Nile tilapia) to salinity tolerance was used through adaptation, selectivity to obtain the optimal O. niloticus tolerates salinity in which reproduction, growth, and metabolic rates will not be significantly affected. Three experiments have been conducted; in the first, the salinity tolerant individuals were selected and the survival rate wasdetermined in different salinity degrees from 6 to 36ppt. In the second experiment, the selected parents, (from the first experiment) were put in serial concentrations of salinity from 6ppt (as control) to 26ppt to determine their spawning ability. In the third experiment, fries of selected parents were reared in different salinity degrees, 6ppt (as control), 12ppt, 16ppt and 20ppt. The rearing period of fries of O. niloticus continued for 84 days. Chemical body composition of the fish and metabolic efficiency were determined at the end of rearing period. There was increase in the mortality ratio by increasing the salinity. Reproduction efficiency decreased with increasing salinity. The fish chemical body composition showed increasing in dry matter, ether and ash while crude protein decreased by increasing salinity. The growth performance increased gradually with increasing salinity concentration from 6 to 16ppt. Optimum salinity of weight gain in O. niloticus was at 16ppt, while 20ppt concentration was the lowest weight gain. In conclusion, the brackish water at 16ppt can be used for rearing O. niloticus without affecting growth rate and reproduction with adequate balanced nutrition.