Combined effects of temperature and salinity on yolk utilization in Nile tilapia (Oreochromis niloticus)

The combined effects of temperature and salinity on the yolk utilization of sac fry in Nile tilapia (Oreochromis niloticus) were investigated using central composite experimental design and response surface approach. Based on the preliminary trials, temperature was determined to range from 22 to 34 degrees C, and salinity ranging from 2 ppt to 10 ppt. The utilization was mensurated in terms of yolk sac volume. Results showed that the linear effects of temperature and salinity on the yolk utilization was significant (P<0.01); the quadratic effects of and the interaction between the two factors were significant (P<0.05); temperature was more important than salinity in influencing the yolk utilization. The model equation of yolk sac volume towards temperature and salinity was established. From those high R-2 values, the model had excellent goodness of fit to experimental data and could be applied for predictive purpose. What with the production cost, it is suggested that the temperature/salinity combination, i.e. 28-30 degrees C/4-6 ppt, be employed during the period of sac fry rearing, in which the yolk utilization was on average 98.6%.