Seasonal histological changes in the gonads of Sebastodes paucispinis ayres,an ovoviviparous teleost (family scorpaenidae)

The elongate paired testes of Sebastodes paucispinis consist of tubules which radiate from a single longitudinal sperm duct and terminate blindly at the periphery of the testis. They are lined by an epithelium consisting of columnar cells with distinct elliptical nuclei. During fall and winter, germ cells migrate inward from the fibrous capsule of the testis and become lodged among the tubule-boundary cells of the seminiferous tubules where they mature into primary spermatogonia. Each of these undergoes several mitotic divisions to produce large cysts of secondary spermatogonia. Subsequent spermatogenic divisions within these cysts produce large sperm-filled cysts which rupture, releasing the spermatozoa into the lumina of the seminiferous tubules. Seasonal cycles of cholesterol and carbohydrate production by the tubule-boundary cells suggest that they perform the same functions as the Leydig cells (androgen production) and Sertoli cells (nutrition) of other vertebrates. The paired fusiform ovaries consist of spongy tissue surrounded by thin-walled muscular ovisacs that converge posteriorly to form a genital duct. The spongy tissue is arranged in transverse lamellae composed of fibrovascular trunks which support epithelial and ovigerous tissue. A series of oocytes (up to 150 μ in diameter) is produced continually from oogonial nests distributed throughout each lamella. Vitellogenesis begins in July and continues throughout the summer. The follicle surrounding the mature oocyte consists of a bilaminar striated vitelline membrane, two epithelial layers (granulosa and theca), and a profuse capillary network. Spermatozoa appear within the ovaries from October to March. Ovulation probably precedes fertilization since spermatozoa were never found within pre-ovulatory or post-ovulatory follicles. The follicular epithelium regresses after ovulation but the capillary beds remain intact, thus providing a mechanism for fetal-maternal exchange of gases and nitrogenous wastes.