Growth comparison among three strains of Oreochromis niloticus juvenilein net cage under different salinity-alkalinity waters

We chose Nile tilapia Oreochromis niloticus juvenile from Shanghai, Shandong and Hebei strains, which were chronically acclimated, as experimental groups, and studied their survival rate and average growth rate in net cage under different salinity water (0, 15, 20), NaHCO3 alkalinity waters (1 gL-1,2 gL-1,3 gL-1), and salinity-alkalinity waters (15, 1 gL-1；15, 2 gL-1;15, 3 gL-1；20,1 gL-1；20, 2 gL-1；20, 3 gL-1). The 62 days experiments show that there is no significant difference in the survival rate between three strains under different salinities, alkalinities and salinity-alkalinity waters (P0.05), while there is significant difference in average growth rate (P0.05). The average growth rate of three strains roughly tend to declinewith increasing salinity and alkalinity, while the growth rate of salinity-alkalinity groupincreasesslower than those of treated with salinity and alkalinity. Besides, Shanghai, Shandong and Hebei strains show some relative growth advantages in different salinity and alkalinity gradients, respectively. The study provides some basic data for determination of optimum growth salinity-alkalinity and for selection of Nile tilapia strain.