Steroid Metabolism in the Blacktip Grouper Epinephelus fasciatus during Oocyte Vitellogenesis

Abstract

We studied oocyte steroidogenesis in blacktip grouper Epinephelus fasciatus ovarian follicles during vitellogenesis. Vitellogenic oocytes with average diameters of 0.45, 0.48 and 0.50 mm were incubated in vitro in the presence of [ 3 H]17α-hydroxyprogesterone as a precursor. The steroid metabolites were analyzed using thin layer chromatography (TLC), high performance liquid chromatography (HPLC), and gas chromatography-mass spectrometry (GC/MS). The major metabolites in the vitellogenic oocytes were androstenedione (A 4), testosterone (T), estradiol-17β (E 2), and estrone (E 1). The metabolites of androgen (A 4 and T) were higher in the 0.50-mm oocytes than in the 0.45-and 0.48mm oocytes, while the estrogen metabolites (E2 and E1) were lower in the 0.50-mm oocytes. These results suggest that 0.50-mm oocytes are fully vitellogenic following initiation of the maturation process.