Eighty units of two-year-old rainbow trout fish weighing between 250-300 gr were used in this study. Experimental gonadectomy was performed on 42 fishes and the rest were used as the control group. The fishes were anesthetised with MS222, then were put on a V-shape table and the fishes remanied under anesthetic with recirculator during the operation. The midline was incised behind the pericardium about 3-4 cm and gonads were removed through gentle traction . The abdominal incision were closed in a single layer in simple interrupted pattern using chromic cat gut no. 1. The sutured incision was covered by Tetramycin ointment, broad spectrum anti-biotic was injected and the fishes were left in fresh water to recover from anesthesia. The fishes were checked after 18, 72 and 141 postoperative days. The surgical time for each fish was 5 ± 1 min, initially was reduced to 3±1 min. At the end the mortality rate was 3 out of operated fishes and one from control group on 72 postoperative day. No .....