Use of diethylstilbestrol and ethynylestradiol to feminize Nile tilapia Oreochromis niloticus (L.) in an outdoor environment

Two synthetic estrogens, diethylstilbestrol (DES) and ethynylestradiol (EE), were orally administered to 8.7 mm gonadally undifferentiated Oreochromis niloticus fry for a period of 28 days in an outdoor setting. Diethylstilbestrol was administered at doses of 100 mg, 200 mg, and 400 mg per kg diet. Ethynylestradiol was administered at 50 mg, 100 mg, and 200 mg per kg diet. One group received a non-hormone-treated feed. Hormone treatments produced significantly more (P < 0.05) than 50% females indicating that genotypic male fish were sex-reversed to phenotypic females. No rate of estrogen administration resulted in a 100% female population. Ethynylestradiol (EE) treatments resulted in 58–65% females, 32–35% males, and 3–9% hermaphrodites. Diethylstilbestrol (DES) treatments resulted in 60–80% females, 13–37% males, and 1–7% hermaphrodites. The DES 400 treatment was the most effective in altering phenotypic sex: 80% females, 13% males, 7% hermaphrodites.