Intraovarian cavity leucocytes of viviparous fish, Neoditrema ransonneti (Perciformes, Embiotocidae)

To obtain basic information on the properties of the intraovarian cavity leucocytes (IOCLs) of the viviparous teleost, Neoditrema ransonneti, morphological characteristics and numerical changes of IOCLs during the reproductive cycle were investigated. In the ovaries of newborn females, leucocytes exuded into the lumen were observed first in November, prior to insemination of semen. These cells were primarily macrophages, neutrophils and lymphocytes. Among them, macrophages were invariably the largest population throughout the reproductive cycle. They began to phagocytize spermatozoa. in December, when spermatozoa were first detected in the ovary. The number of IOCLs gradually increased from November in the newborn female. However, this increase is not ascribed to the effect of copulation or the presence of semen, because the number of leucocytes also increased in non-mating fish. While developing embryos were discharged into the ovarian lumen at the latest in January, a number of spermatozoa and spermatozoa-phagocytizing macrophages were seen until March. Even after the extinction of sperm cells, numerous IOCLs remained in the lumen and coexisted with fetuses until their parturition. These results suggest that IOCLs play roles in successful pregnancy, besides elimination of remaining spermatozoa.