Variation with reproductive status of PGE2 receptor immunoreactivities in the Bostrichthys sinensis olfactory system

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