Morphological changes and competence of maturing oocytes in the protandrous black porgy, Acanthopagrus schlegeli

The study objectives aimed to investigate the morphological changes of oocy tes during final oocyte maturation and ovulation, and the maturational comp etence of oocytes to respond to maturation-inducing steroids in the protand rous black porgy, Acanthopagrus schlegeli. Females were injected with 2 suc cessive doses of LHRH analog (10 and 50 mu g per fish) on days 0 and 1. The oocytes were obtained at 6- or 3-h intervals from the genital pore after t reatments. Morphological changes during oocyte maturation and ovulation wer e observed, and oocyte diameters in in vitro culture (with or without hormo nes) were measured. Oocyte maturation and ovulation occurred at 20-28 h and 36-60 h after the 2nd LHRH-A injection, respectively. It took 4-8 h to com plete the process of oocyte maturation (in vivo) and 40 min for ovulation ( in vitro). Hormones (17,20 beta-dihydroxy-4-pregnen-3-one, 17,20 beta,21-tr ihydroxy-4-pregnen-3-one, and HCG) could significantly induce oocyte matura tion in oocytes collected at 9 and 6 h prior to the occurrence of germinal vesicle breakdown (GVBD). Oocyte maturation spontaneously occurred in oocyt es collected at 3 h prior to GVBD. HCG showed no synergistic effects with s teroids in the induction of oocyte maturation.