Exposure of Red Tilapia (Oreochromis spp.) eggs to 17α-Methyltestosterone and the sex ratio of the fish offspring

This study evaluated the proportions of sex reversals which occurred after red tilapia (Oreochromis spp.) eggs were immersed into various solutions of 17 alpha-Methyltestosterone (0, 800 and 1200 mu g/L of water). Two fertilization stages of the eggs, i.e., reflecting clear or dark colors, were included in this study. Besides sex proportions, other parameters studied included hatching, fry and fingerling survival, final weight and length. There were no significant differences between the sex proportions obtained relative to hormone concentration or egg color (49.59% males from dark eggs and 46.36% males from light eggs versus the control, which had 55.24% males). In contrast, the percentage of hatching was significantly higher in dark eggs (60.27% +/- 11.52). Survival of fry was higher when born from dark eggs compared with clear eggs (51.74% +/- 27.01 versus 28.97% +/- 1.52, respectively). Fingerling survival was not related to the color of the eggs (59.28% +/- 23.73 versus 65.58% +/- 9.01 for initially dark and clear eggs, respectively). However, surviving males were longer and heavier (6.75 cm +/- 1.29 and 5.45 g +/- 3.09) than females. This data suggest a possible interaction between hatching, survival, and egg color.