Regulation of Oocyte Maturation in Fish

This chapter describes the different aspects of the regulation of oocyte maturation in fish. Teleost fishes have full-grown postvitellogenic oocytes in the ovary that are physiologically arrested at the G2/M border in the first meiotic prophase and cannot be fertilized. The full-grown oocyte of teleosts possesses a large nucleus in meiotic prophase. The germinal vesicle of this stage is generally located centrally or halfway between the center and the oocyte periphery. The ovarian follicle layer of teleosts, as in other vertebrates, consists of two major layers: (1) the thecal layer, containing fibroblasts, capillaries, collagen fibers, and large glandular cells designated as “special thecal cells” and (2) the granulosa layer, composed of a single population of granulosa cells. In a number of teleost species, the eggs of mature females can be induced to mature and ovulate by the injection of a variety of gonadotropin preparations. It has been found that follicle-enclosed, full-grown, and postvitellogenic oocytes of several teleosts undergo the breakdown of the germinal vesicle in vitro when they are incubated with a number of gonadotropin preparations. It has also been observed that in addition to specific gonadotropin receptors, crude membranes of amago salmon granulosa cells contain guanine nucleotide-binding regulatory proteins and adenylyl cyclase.