Milt and endocrine responses of mature male Atlantic salmon (Salmo salar L.) parr to water-borne testosterone, 17,20 beta-dihydroxy-4-pregnen-3-one 20-sulfate, and the urines from adult female and male salmon.

Mature male Atlantic salmon (Salmo salar L.) parr responded to the urine from ovulated females with significant increases in plasma gonadotropin II, 17,20 beta-dihydroxy-4-pregnen-3-one, testosterone, and 11-ketotestosterone concentrations and volumes of expressible milt. There were also significant increases in biliary free steroid and steroid conjugate concentrations. Urine from mature adult male salmon also affected male parr, which responded with increased plasma gonadotropin II concentrations and expressible milt. However, male urine did not elevate the plasma and bile concentrations of any of the steroids. When two of the three known steroids which are detected by the mature male salmon parr olfactory epithelium were tested for priming activity, results showed that these compounds had little or no activity when added to the water. Only plasma gonadotropin II concentrations increased in mature male parr exposed to 17,20 beta-dihydroxy-4-pregnen-3-one 20-sulfate. Female and mature adult male urines contain at least one priming pheromone and there was no conclusive evidence for this priming pheromone being one of the tested steroids. However, the fact that water-borne 17,20 beta-dihydroxy-4-pregnen-3-one 20-sulfate can have a physiological effect in male parr suggests that it may have a role as one of a mixture of compounds in female urine that males detect and respond to. The lack of a priming-like effect of testosterone supports a previous hypothesis that the major pheromonal role of this steroid is as an attractant for mature male salmon parr.