Androgen levels and social interactions in breeding males of the peacock blenny

Nest-holder male Salaria pavo have lower circulating concentrations of 11-k etotestosterone (KT) at the beginning of the breeding season than at its pe ak. At that peak density or nesting males was higher as were the number of L visits of sneaker males to nests and of agonistic Interactions between ne st-holders and sneaker males. There was no difference between the two dares either in the frequency of male male interactions or in the frequency or c ourtship episodes. Thus. higher plasma levels in nest-holders might be expl ained by a more intense sneaking pressure at the peak of the breeding seaso n. At that peak, nest-holders had higher plasma levels of KT and a higher t estosterone (T) to KT metabolization index in the gonads than did floater m ales. Both nest-holders and floaters had higher level of KT and T in the te sticular gland than in the testis. The levels of both androgens in the test icular gland. but not in the ti is, were correlated with circulating concen trations of KT. These results suggest that the testicular gland is the majo r source of circulating KT in blenniids. Nest-holders had higher metaboliza tion indexes than floaters both in the testis and in the testicular gland. which suggests that nest holding status promotes the conversion of T into K T. (C) 2001 The Fisheries Society of the British Isles.