Effect of water temperature, salinity, and their interaction on growth, plasma osmolality, and gill Na+, K+-ATPase activity in juvenile GIFT tilapia Oreochromis niloticus (L.)

Abstract

We used a central composite rotatable experimental design and response surface methodology to evaluate the effects of temperature (18–37°C), salinity (0–20‰), and their interaction on specific growth rate (SGR), feed efficiency (FE), plasma osmolality, and gill Na+, K+-ATPase activity in GIFT tilapia juveniles. The linear and quadratic effects of temperature and salinity on SGR, plasma osmolality, and gill Na+, K+-ATPase activity were statistically significant (P<0.05). The interactive effects of temperature and salinity on plasma osmolality were significant (P<0.05). In contrast, the interaction term was not significant for SGR, FE, and gill Na+, K+-ATPase activity (P>0.05). The regression equations for SGR, FE, plasma osmolality, and gill Na+, K+-ATPase activity against the two factors of interest had coefficients of determination of 0.944, 0.984, 0.966, and 0.960, respectively (P<0.01). The optimal temperature/salinity combination was 28.9°C/7.8‰ at which SGR (2.26%d1) and FE (0.82) were highest. These values correspond to the optimal temperature/salinity combination (29.1°C/7.5‰) and the lowest plasma osmolality (348.38mOsmolkg−1) and gill Na+, K+-ATPase activity (1.31µmolPi.h−1g−1 protein), and resulted in an energy-saving effect on osmoregulation, which promoted growth.