Thermal and hormonal feminization of all male YY Nile tilapia, Oreochromis niloticus L.

Hormonal and thermal sex reversal of YY male Oreochromis niloticus were compared. While similar percentages of females (34% and 32%, respectively) were produced, a significantly higher percent of intersex individuals (18.5%) was produced in the heat (36 degreesC) treatment than in the group treated with diethylstilbestrol (DES; 1.6%). The heat-treated groups had 62.6% survival, compared to 97.0% and 97.3% in the control and DES-treated groups, respectively. Our results demonstrate that a high temperature treatment can be an alternative to hormonal sex-reversal treatments for YY male O. niloticus. Although the low survival and high occurrence of intersex individuals may limit its use, it can be used to produce large numbers of YY male broodstock in countries where hormone use is illegal and/or consumer reaction to hormonally-treated fish is negative.