The role of PGE2 as a putative sex pheromone in Chinese black sleeper Bostrichthys sinensis was investigated, using immunocytochemistry and how the immunoreactivities of the prostaglandin E2 (PGE2) receptor subtypes EP1, EP2, EP3 and EP4 varied with reproductive status in the olfactory system was determined. The results showed that PGE2 receptors were present in the whole of the olfactory system of B. sinensis, and that the number of receptors was linked to the reproductive status of the fish. The densities of EP1 immunoreactivity in the olfactory epithelium of mature fish were significantly (P < 0·01) higher than those in immature fish of both sexes, and the densities of EP2 and EP3 immunoreactivities in mature fish were higher (but not significantly) than those in immature fish of both sexes. In the olfactory nerve, the density of EP2 immunoreactivity in mature fish was higher (but not significantly) than that in immature fish in both sexes. In the olfactory bulb, the densities of EP1–4 immunoreactivities in mature females were significantly (P < 0·05 or <0·01) higher than those in immature females, and the density of EP4 immunoreactivity in mature males was significantly (P < 0·01) higher than that in immature males. As far as is known, the present study is the first report of the immunoreactivities of PGE2 receptor subtypes in the olfactory system of a teleost, and offers new findings regarding the role of PGE2 as sex pheromone and hormone in the reproductive behaviour and pheromonal communication of B. sinensis.