AVOIDANCE OF A PUTATIVE PHEROMONE, 17-ALPHA,20-BETA-DIHYDROXY-4-PREGNENE-3-ONE, BY PRECOCIOUSLY MATURE CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA)

To test the hypothesis that the gonadal steroid, 17 alpha,20 beta-dihydroxy-4-pregnene-3-one (17 alpha,20 beta-P) acts as a pheromone for mature male salmon, we examined the behavioral responses of precociously mature chinook salmon (Oncorhynchus tshawytscha) to this odorant. These males avoided water scented with 17 alpha,20 beta-P in a two-choice maze. This avoidance response was not shown by immature chinook salmon of the same age or by mature males to a second steroid hormone, testosterone. Taken together, these results suggest that 17 alpha,20 beta-P is a behaviorally relevant odorant for precociously mature male salmon. The avoidance response observed may reflect the sneaker spawning tactic employed by precociously mature fish, as attraction to the odorant was predicted for mature males in general.