[Synergistic effects of water temperature and salinity on the growth and liver antioxidant enzyme activities of juvenile GIFT Oreochromis niloticus].

By adopting two-factor central composite design (CCD) and response surface methodology (RSM), this paper studied the synergistic effects of water temperature (16-37 degrees C) and salinity (0-18) on the specific growth rate (SGR) and liver superoxide dismutase (SOD) and catalase (CAT) activities of juvenile GIFT Oreochromis niloticus. Water temperature and salinity had significant linear and quadratic effects on the SGR (P < 0.05), respectively. With increasing water temperature or salinity, the SGR decreased after an initial increase. There existed significant synergistic effects between water temperature and salinity (P < 0.05). The SGR was higher at 16-20 degrees C and salinity 9-10, at 27-32 degrees C and salinity 3-5, and at 35-37 degrees C and in freshwater. The SOD and CAT activities were higher at 28-30 degrees C and salinity 6-8. The linear of temperature and quadratic of salinity had significant effects on the two enzymes (P < 0.05), and there was a significant synergistic effect on CAT activity. High temperature and high salinity were not favorable to the expression of SOD and CAT activities. The coefficients of determination of quadratic regression equations for SGR, SOD and CAT activities reached to 0. 954, 0. 831, and 0. 942 (P < 0. 05), respectively, and could be used for prediction. The growth and antioxidant enzyme activities were more affected by water temperature than by water salinity. In the culture practice of 0. niloticus, it would be necessary to optimize culture environment and reduce oxidative stress to promote the growth and disease-resistance of the tilapia.