Effect of high temperature during embryogenesis on the sex differentiation process in the Nile tilapia, Oreochromis niloticus

The aim of the present study was to environmentally (with temperature) modify the normal pathway of sexual differentiation during embryogenesis in Nile tilapia. Shortly after natural reproduction (< 12 h) between XX males and XX females, spawns (n = 4) of tilapia were incubated at 27 °C (control group), 34, 35 and 36 °C for the rest of the embryonic development. After 3 months of rearing, 100 fish (MBW = 3–6 g) per batch were sacrificed and the sex ratio determined with the acetocarmine squash method. Survival rate at hatching significantly decreased with increasing temperature (49.5% and 29.8% at 27 and 36 °C respectively). Sex ratios of the control group (27 °C) were 100% females whereas a significant proportion of males (from 6.0 to 26.7%) appeared in all treated groups. The mean percentage of males was increased in high temperature: 9.7, 18.2 and 17.5% of males at 34, 35 and 36 °C respectively. These results prove for the first time the possibility to modify the normal pathway of sexual differentiation during the embryonic development of Nile tilapia, before the apparition of the reproductive system.