The behavioural response of spermiated male goldfish to the sex pheromone 17alpha,20ss-dihydroxy-4-pregnen-3-one (17alpha,20ss-P) in the ambient water was measured using a computerized video-image analysis system. The position and spontaneous locomotor activity of single spermiated male goldfish were continuously recorded in an artificial stream. 17alpha,20ss-P (final concentration 10(-11) mol l-1) was supplied to one half and its ethanol carrier to the other half of the test area. The results showed that the fish spent significantly less time in water scented with 17alpha,20ss-P than in control water. Moreover, both the spontaneous locomotor activity and the gonadotropin II concentration in the plasma increased significantly because of contact with 17alpha,20ss-P in the ambient water. The swimming speed was unchanged, whether the fish resided in the 17alpha,20ss-P section or in the section without 17alpha,20ss-P added. In view of the complex dual hormone-pheromone system in goldfish, the possibility of an additional function of 17alpha,20ss-P is discussed. Because the release of the pheromone 17alpha,20ss-P occurs before ovulation and the level then drops drastically, we suggest that the avoidance reaction observed allows the sexually mature male to avoid misdirected courting of non-ovulated females and thus to continue its search for an ovulated female.

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