Masculinization Effect of 17 alpha -Methyl Testosterone on Developmental Stages of Guppy

The masculinization effects of 17α-methyltestosterone were investigated on the two developmental stages of guppy (Poecilia reticulate), namely, newly born fry and gravid females. The first group was treated with two doses of androgen, (30 and 60 mg/kg food), each for a period of 15 and 30 days and the second group (gravid females) was treated with the food doses of 400, 450 & 500 mg/kg in a 10 day duration prior to parturition. After three months, the first group masculinization ratio of 62.14% was attained only in 60 mg/kg at three-day long treatment and other treatments had no significant effect on masculinization. In this group all the treated fish developed male secondary sexual characteristics after 3 or 4 weeks. However, the above-mentioned characteristics disappeared gradually when hormone therapy was stopped. In the second group, all the treatments were significantly different from control group. 450 and 500 mg/kg treatments had the highest masculinization percentage (90.82 and 97.07, respectively) but the differences were not significant. Also there were 9.18% females in 450 mg/kg treatment and 2.93% intersex in 500 mg/kg treatment. But the so-called group mortality was higher and fecundity lower than those in the control group. Finally, it should be noted that hormonal treatment had not any significant effect on masculinization of newly born fry and with the regard to the effect of 450 mg/kg treatment on masculinization and mortality percentage, it can be introduced as the best treatment.