Species-specific releaser effect of urine from ovulated female masu salmon and rainbow trout

MT (17α-methyltestosterone)-treated immature masu salmon Oncorhychus masou and rainbow trout Oncorhynchus mykiss , exposed to the urine of ovulated females in their non-reproductive season, made significantly more entries into the channel, of a Y-maze preference trough, conditioned by the urine of conspecific females than by heterospecifics. Immature, non-treated controls in both species showed no preference for the urine of ovulated females. These results suggest that, for both species, the releaser pheromones that attract males in the urine are species-specific. Therefore, utilization of species-specific chemical signals may be one of the mechanisms of the reproductive isolation in Oncorhynchus species.