Abstract

In our study the effect of 17a-methyltestosterone soluted in water for masculinization of fighting fish, Betta splendens Regan, was investigated. The fish at age of 12, 17, and 22 days were treated in solution of 0.1, 0.2; 0.5; 1.0; 2.5; and 5.0 ppm of MT. Duration of each treatment is 3hrs. The male ratio were 60.51; 64.53; 63.74; 76.46; 83.03; and 84.16%; respectively. The survival rate were 78.67; 75.67; 74.33; 74.00: 71.00; and 69.00%; respectively. Dietary treatment with MT at 40 ppm applied at the age of fry of 21 days and lasted for 30 days produced 83.72% of male fish with death rate of 63.00%. We would like to introduce the conception "effectiveness of masculinization" [(male ratio of treatment-male ratio of control) x survival rate / female ratio of control]. This value is highest at 2.5 ppm and 5.0 ppm (49.55% and 49.54%) of imersion treatment, and higher than that of dietary treatment (42.27%).