Optimization of culture conditions for larval GIFT tilapia Oreochromis niloticus using response surface methodology and effects of HAMP-1 and c-type lysozyme mRNA expression in liver.

Response surface methodology (RSM) in concert with central composite experimental design was firstly applied to optimize the culture condition for larval Genetically Improved Farmed Tilapia (GIFT) tilapia. Larvae were reared at different water temperature (16-37 °C) and salinity (0-20 ‰) for 35 days. Results showed that the linear and quadratic effects of temperature and salinity on specific growth rate (SGR), survival and hepatic HAMP-1 mRNA levels were statistically significant ( P < 0.05). The interacting effects of temperature and salinity on SGR and survival were significant ( P < 0.05), but the interaction on the levels of hepatic HAMP-1 and c-type lysozyme mRNA was not significant ( P > 0.05). A significant increase in the levels of c-type lysozyme mRNA was observed as salinity increases; the quadratic effects of salinity were insignificant ( P > 0.05). The regression equations of SGR, survival, the levels of hepatic HAMP-1 and c-type lysozyme mRNA toward the two factors of interest were established using multiple regression analysis, with the coefficients of determination being 0.980, 0.982, 0.968, and 0.949, respectively ( P < 0.01). Based on RSM, the optimal temperature/salinity combination was obtained at 28.2 °C/6.8 ‰ of which the greatest SGR (10.08 % day) and survival (91.34 %) were simultaneously attained. Adequately increasing salinity would improve growth, survival, and innate immune function in larval GIFT tilapia. [ABSTRACT FROM AUTHOR]