), and that the pheromones are likely detected through the olfactory system by 17α-P receptors (PRs) and PGE₂ receptors (EPs). During the spawning season, after mature for 24 h and 48 h, we measured the ovulation rates and quantified the immunoreactivities of PR and EPs in the olfactory system using SABC immunocytochemistry. The ovulation rates of females increased after exposure to 17α-P or PGE₂ for 24 h and 48 h. Furthermore, the rate was the higher after 48 h exposure than after 24 h exposure. The increase in numbers of PR and EPs immunoreactive cells was the highest in the olfactory epithelium, followed by the olfactory bulb, and the olfactory nerve was the lowest exposed to 17α-P or PGE₂. The increases in the number of PR and EPs immunoreactive cells were consistent with the increases in ovulation rate. Our results suggest that water-borne 17α-P and PGE₂ affect the reproductive status of and EPs in the olfactory system. We also discuss the potential mechanisms of sex pheromone reception and transduction in the olfactory system.