Effect of fluoxymesterone on sex ratio and growth of Nile tilapia, Oreochromis niloticus (L.)

The androgenic and anabolic potential of fluoxymesterone (FM) was evaluated by incorporating the hormone into the feed of Nile tilapia, Oreochromis niloticus(L.) fry. Phenotypic all-male populations were produced when FM was given at 1, 5 and 25mg/kg of feed. Fry fed methyltestosterone (MT) at 60 mg/kg of feed and 0-2 mg of FM per kg of feed had a sex ratio of 97-7% and 87-3% phenotypic males. No positive anabolic effect was evident in response to adding FM or MT to the feed at the end of the 28-day treatment period or after an additional 6 weeks of growth without hormone. Growth was less for fry which received 25 mg/kg of FM compared to those receiving lesser rates of FM, 60 mg/kg MT, and controls.