Zoological Studies

Vol. 39 No. 2, 2000

Morphological Changes and Competence of Maturing Oocytes in the Protandrous Black Porgy, Acanthopagrus schlegeli

Wen-Shiun Yueh and Ching-Fong Chang*

Department of Aquaculture, National Taiwan Ocean University, Keelung, Taiwan 202

Wen-Shiun Yueh and Ching-Fong Chang (2000) The study objectives aimed to investigate the morphological changes of oocytes during final oocyte maturation and ovulation, and the maturational competence of oocytes to respond to maturation-inducing steroids in the protandrous black porgy, Acanthopagrus schlegeli. Females were injected with 2 successive doses of LHRH analog (10 and 50 g per fish) on days 0 and 1. The oocytes were obtained at 6- or 3-h intervals from the genital pore after treatments. Morphological changes during oocyte maturation and ovulation were observed, and oocyte diameters in in vitro culture (with or without hormones) 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 complete the process of oocyte maturation (in vivo) and 40 min for ovulation (in vitro). Hormones (17,20β-dihydroxy-4-pregnen-3-one, 17,20β,21-trihydroxy-4-pregnen-3-one, and HCG) could significantly induce oocyte maturation in oocytes collected at 9 and 6 h prior to the occurrence of germinal vesicle breakdown (GVBD). Oocyte maturation spontaneously occurred in oocytes collected at 3 h prior to GVBD. HCG showed no synergistic effects with steroids in the induction of oocyte maturation.

Key words: Black porgy, Maturation-inducing steroid, Oocyte culture, Oocyte growth, Oocyte maturation.

*Correspondence: Tel: 886-2-24622192 ext. 5209. Fax: 886-2-24621579. E-mail: b0044@mail.ntou.edu.tw