Effects of natural androgens and corticosteroids on gonad differentiation in the rainbow trout, Salmo gairdneri.

Rainbow trout fry were treated with equimolar quantities of cortisol, cortisone, androstenedione, and 11 beta-hydroxyandrostenedione, added to the aquarium water during a 4-week period. All four steroids inhibited ovarian growth. Androstenedione did not influence gonadal sex differentiation; the other steroids pushed the sex ratio in the male direction. However, a near to normal sex ratio was observed 300 days after the 11 beta-hydroxyandrostenedione treatment. When added to the food in two different doses during 8 weeks, 11 beta-hydroxyandrostenedione had a pronounced masculinizing effect, and androstenedione did not modify the gonads at all. It is suggested that the two exogenous corticosteroids were probably converted into 11-oxygenated androstenedione derivatives, and that these 11-oxygenated androstenedione derivatives are particularly important in sustaining the differentiation and early development of the testes in rainbow trout. Testosterone does not seem to be indispensable for these processes, because two different doses of testosterone-blocking cyproterone acetate, added to the food for 8 weeks, failed to affect early gonad development.