Oreochromis niloticus(NEW GIFTS) and their hybrid F1 and F2 generations. Groups of 10 juveniles (10 to 14 g) of each species/hybrid generation were reared in freshwater then subjected to a gradual increase in salinity (8/d) until all fish died. Control fish were held in fresh water. and the fish were fed daily. The median lethal salinity (MLS) was 125.78±1.66, 54.22±2.51, 77.33±1.89, and 73.73±1.32 for , F1, and F2, respectively. The mean cumulative survival (CS) and MLS were significantly higher in and the F1 and F2 hybrids. Similarly, the CS and MLS were significantly higher in the F1 and F2 groups than in but there was no significant difference between the F1 and F2 groups (>0.05).