RESUMO
The attractive response and sexual activity elicited by pre-ovulatory steroid sulphate and post-ovulatory 15K-PGF pheromones are greater in wild caught tubercular males and immature males which express breeding tubercles on the snout (at 12-13 days post androgen implant) than in non-tubercular and non-androgen implanted males of freshwater fish Barilius bendelisis. This shows that circulatory androgens exert an activational effect on olfactory receptors of male fish. Wild caught tubercular males and androgen implanted juvenile males exhibit a high responsiveness to steroid sulphate at the water temperature and pH which fish experience during the pre-spawning phase. The male's sensitivity to 15K-PGF is almost equally high at the water temperature and pH which they experience in wild during the both pre-spawning and spawning periods. This suggests that the differential olfactory sensitivity to the two classes of pheromones in androgen implanted males is due to the varied temperature and pH of water, and that during the breeding season the male's olfactory sensitivity to PGF pheromone is more widespread than to the steroidal pheromone. An increased and decreased olfactory sensitivity in mature males to sex pheromones and L-alanine respectively during the breeding phase is in agreement with the hypothesis that pheromonal stimuli dominate over feeding stimuli to promote spawning success.