Effects of Low Salinity on Growth, Survival, and Stress Response in the Longtooth Grouper, Epinephelus bruneus, and E-bruneus x E. lanceolatus Hybrid Grouper

This study investigated the effects of low salinity on growth, survival, and stress response in longtooth grouper, Epinephelus bruneus, and the hybrid grouper resulting from crossing E. bruneus females and E. lanceolatus males. There were no significant differences in the hybrids for any of the above growth values among different salinity groups, however the percent weight gain was significantly lower in the 8 Practical Salinity Unit (psu) group than in the other salinity groups. As for survival, only longtooth grouper in the group reared at 8 psu died. The plasma cortisol levels tended to increase at lower salinities in both the longtooth grouper and the hybrids. Plasma Na+, K+, Cl- concentrations in the hybrid were not significantly different among the salinity groups, while Na+ and Cl- concentrations in the longtooth grouper were significantly lower in the 8 psu group than in the other treatments. The above results indicate that both the longtooth grouper and the hybrid grouper juveniles were highly adaptable to variations in salinity. The optimal salinity for rearing longtooth grouper was found to be 24 psu, while the hybrids had a larger tolerance range of 16-32 psu. Results therefore showed that the hybrid grouper has a higher tolerance than the longtooth grouper for low salinity.