Macroscopic and microscopic characteristics of the maturity stages of the ovary of the amberjack Seriola dumerili, Risso are reported. Oogonia, oocytes at different stages of development, follicular and thecal cells, and postovulatory follicles are described following a light and transmission electron microscope study. Histological observations of oocyte development show that the oocyte diameter increases about 100-fold during oogenesis, the nucleus-to-cytoplasm-ratio ranging from 72% (in oogonia) to 18% (in mature oocytes just before the breakdown of the germinal vesicle). Histochemical and ultrastructural studies show that three types of inclusions are formed during vitellogenesis. Lipid globules (exclusively composed of neutral lipids) appear first (at the end of the perinucleolar stage) followed by cortical alveoli (exclusively composed of carbohydrates). Yolk granules, which contain glycoproteins, glycogen and lipids appear last. The location and movements of these inclusions within the oocyte cytoplasm during oogenesis are described. The vitelline envelope or zona radiata (ZR) is first seen at the lipid globule stage I as a discontinous layer. This structure, mainly proteinaceous in nature, increases in thickness as oogenesis proceeds and peaks (33 μm) during the maturation phase.
|Publication status||Published - 1 Dec 1996|