Optimization of treatment regimes for controlled sex differentiation and sterilization in wild rainbow trout ( Salmo gairdneri Richardson) by oral administration of 17α-methyltestosterone

Abstract

The oral administration of 17α-methyltestosterone (MT) to wild rainbow trout fry at concentrations ranging from 1 to 100 mg/kg diet for periods up to 120 days following swim-up produced male-female ratios substantially different from controls. 100% males were produced with low MT doses (1, 3 and 9 mg/kg diet) administered for 60 days. High proportions (79–90%) of sterile rainbow trout were obtained with greater doses of the steroid (25, 50 and 100 mg/kg diet) fed for 120 days. A paradoxical feminizing effect at high doses of MT (50 and 100 mg/kg diet) was observed irrespective of the length of the treatment. No dose-related mortality during the treatments was observed.