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.)

We used a central composite rotatable experimental design and response surface methodology to evaluate the effects of temperature (18-37 degrees C), salinity (0-20 parts per thousand), 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 degrees C/7.8 parts per thousand at which SGR (2.26% d(1)) and FE (0.82) were highest. These values correspond to the optimal temperature/salinity combination (29.1 degrees C/7.5 parts per thousand) and the lowest plasma osmolality (348.38 mOsmol kg(-1)) and gill Na+, K+-ATPase activity (1.31 mu mol Pi. h(-1) g(-1) protein), and resulted in an energy-saving effect on osmoregulation, which promoted growth. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.