Effect of dietary supplementations of 17 A-methyltestosterone and aromatase inhibitor (Fadrozole) on sex ratio of Oreochromis niloticus fry [electronic resource].

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In Egypt, the widespread application of honnonal sex reversal using 17 0methyltestosterone (17 MT) in the production of all male sex reversed tilapia has led to considerable pollution of the hatchery environment with that hormone and its metabolites accordingly, there is urgent need to reduce the amount used of this potentially cClrcinogenic honnone. The aim of the present work is to reduce (as much as possible) the amount of MT needed to produce all-or nearly all male tilapia fry through the combined use of an aromatase inhibitor. A specific non-steroidal aromatase inhibitor "Fadrozole" was added alone or in combination with 17 MT at different proportions to fry feed to find out the most appropriate effective lowest dose of both drugs for sex reversal in O. niloticus. Fish fry were fed the treated feed for 30 days after which final weight, survival rate and sex ratio were monitored. Results showed that the best growth was achieved when a combination of 9 mg 17 MT plus 20 mg fadrozolel kg feed were used. However the best survival rate was observed in fry group fed on 70 mg fadrozole/kg feed. The highest sex reversal (96 % males) along with the lowest dose of 17 MT was observed in fry treated with of 9 mg 17 MT plus 20 mg fadrozole/kg feed. The results of the present work point to the possibility of lowering the commonly used dose of 17 MT (30-60 mg/Kg feed) to 9 mg/Kg feed only through combined addition of fadrozole at 20 mg/Kg feed. However, further studies are needed to reveal the possible health impact of fadrozole.

Summary in Arabic.

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