Sperm maturation, migration, and localization before and after copulation in black rockfish (Sebastes schlegelii)

Sebastes schlegelii is a typical viviparous teleost with six months sperm storage duration from November to April. In this study, spermatozoa morphological and physiological characteristics and sperm location in the female ovary were investigated by electron microscopy, computer-assisted sperm analyzer and histologic analysis, respectively. During copulation, we observed that spermatozoa in the testis had mature structure with rod-shaped head, a short midpiece, and a long flagellum. And further verified sperm swam freely at a high speed in the ovary fluid. After copulation, we only found swimming sperm in the ovary fluid at the early storage stage (November to December) and the majority of sperm were scattered randomly in the ovary cavity and partially concentrated in the crypt between the oocyte and stalk of follicle. Thereafter, the ovarian epithelium around the oocytes proliferated rapidly and wrapping spermatozoa outside of the follicular layer and formed a lot of crypts outside of the follicular layer which served as the sperm storage site until fertilization. The present findings would be useful for further understanding the mechanism of long-term sperm storage in viviparous teleost.