[Ultrastructure of the steroidogenic cells in the ovary of the Russian sturgeon before and after maturation under exposure to luliberin].

Cells with the ultrastructure typical of steroid cells of vertebrates were found in the theca and stroma of the Russian sturgeon ovary. Mitochondria with the tubulo-vesicular internal structure, smooth and rough endoplasmic reticulum, lipid droplets or liposomes were observed in the cytoplasm of these cells. After the ovulation of fishes, the volumetric density and mean diameter of cell mitochondria and of the reticulum are found to increase; besides, mitochondria are seen vacuolized. The ultrastructural changes may indicate that the production of steroid sex hormones is more intensive in fish during ovulation. These suggestions are in accordance with biochemical data available in the literature.