Effect of oral administration of different levels of 17α- methyltestosterone on the sex reversal, growth and food conversion efficiency of the tilapia Oreochromis spilurus (Günther) in brackish water

Abstract. The effect of oral administration of 17α-methyltestosterone (17-MT) to Oreochromis spilurus (Günther) in brackish water (3-5 ppt) was studied in terms of masculinization, growth, food conversion efficiency (FCE), specific growth rate (SGR) and survival rate. A 38-day hormone treatment followed by 205 days of normal diet yielded a higher percentage of males, differing significantly from the normal 1:1 ratio. The highest proportion of males (90-3%) was in the replicates given 70 mg/kg of 17-MT. After the hormone treatment phase, no effects were observed on growth, FCE, SGR and survival rate. At the end of the experiment (243 days), the treated groups showed significant increases in growth, SGR and FCE. The 50 mg/kg replicates showed the highest growth and SGR, and the 70 mg/kg groups the highest FCE. The maximum survival rate was in the controls, and the minimum in the 50 mg/kg groups. It can be concluded that the androgen-induced sex reversal in O. spilurus is comparable to that in other tilapia species. However, further studies should be carried out to determine the optimum dose and duration to achieve 100% masculinization.