Masculinization of genetic female Nile tilapia (Oreochromis niloticus) by dietary administration of an aromatase inhibitor during sexual differentiation

A series of experiments was carried out in which genetically female Nile ti lapia (Oreochromis niloticus) fry were treated with Fadrozole, a nonsteroid al aromatase inhibitor (AI), in the diet during the period of sexual differ entiation. Batches of tilapia fry treated with AI during the first 30 days following yolk-sac resorption (7-37 days post hatch, dph) showed a dose-dep endent increase in the percentage of males from 0 to 200 mg.kg(-1). The per centage of males remained approximately constant (92.5-96.0%) from 200 to 5 00 mg.kg(-1) Any continuous 2- or 3-week treatment with 500 mg.kg(-1) AI in this 4-week period successfully masculinized the majority of the treated f ish (>80%). Treatments of 1 week duration revealed that the most sensitive time to Al lies in the first week (between 7 and 14 dph). Progeny testing o f males from AI-treated groups gave results indicating that these were XX m ales, as expected. These experiments strongly implicate aromatase activity as a key factor in sexual differentiation in the Nile tilapia. (C) 2000 Wil ey-Liss, Inc.