The present study deals with the effect of temperature on the development of different tilapia species (O. niloticus, red tilapia, O. aureus and hybrid tilapia (O. niloticus x O. aureus)) during larval rearing, and its subsequent effect on larval
growth and survival. The development of the gills and the digestive tract was investigated histologically and histochemically in the developing control and temperature-exposed larvae of different tilapia species. The exposure of different tilapia species larvae to moderate level of temperature (25-35ºC) with a mean of 30ºC greatly enhanced the development of gills and the digestive system of larvae as indicated by the quantitative and qualitative changes of the mucus composition from predominantly neutral to a mixture of neutral and acid mucosubstances, or acid
mucosubstances occurred during the rearing period. This may be due to the direct effect of temperature on food intake and increasing of metabolism, enhanced the immunity of larvae or indirect effect of temperature on sex differentiation andproducing high percentage of males which have rapid growth rate than females. Thus, rearing temperature directly or indirectly improved larval growth of different tilapia species, since a marked increase in both, length and weight of larvae occurred during the experimental period. In addition, temperature-exposed larvae also gave a
significantly higher survival rate than that of control. It could be concluded that the exposure of different tilapia species larvae to a rearing temperature of 30ºC was effective for improvement of development and growth in a safe, simple and acceptable manner, as well as in a friendly approach to the environment.