Androgens and behaviour in the three-spined stickleback

In vitro incubations showed 11-ketoandrostenedione (11KA) to be the main androgen produced by the testes of the breeding stickleback. In breeding males the plasma levels of 11-ketotestosterone (11KT) are higher than those of other measured androgens, and display a clear peak in the breeding season. 11KA can be converted extra-testicularily to 11KT. In breeding females the plasma levels of 11KT are lower than in breeding males, whereas the opposite is the case for testosterone. Castration leads to the disappearence of male reproductive behaviour and secondary sexual characters. 11-androgens are more effective than other androgens in stimulating secondary sexual characters, notably kidney hypertrophy. All aspects of male reproductive behaviour can be restored in castrated males with 11KA capsules. 11KA was more effective than other tested androgens in this respect. The effectiveness of 11KA on nesting is not influenced by photoperiod.