The histological changes in the ovary of sevenband grouper Epinephelus septemfasciatus were examined during vitellogenesis and final oocyte maturation. Ovaries contained oocytes at the perinucleolus stage at the start of the experiment in January. Oocytes at the primary yolk stage appeared when the gonadosomatic index (GSI) was slightly on the rise in March. After that, vitellogenesis progressed and ovaries contained oocytes at the tertiary yolk stage in May. The GSI increased drastically at the same time. These results suggest that vitellogenesis in sevenband grouper starts or is already in progress in March and is completed by May, In order to clarify the process of final oocyte maturation, luteinizing hormone-releasing hormone (LHRH) analog (des Gly 10 , [D-Ala 6 ] LHRH ethylamide) was implanted in fish with oocytes at the tertiary yolk stage. The oocytes developed to the migratory nucleus stage in 18 h and reached the maturation stage in 42 h after implantation. This indicates that final oocyte maturation is completed within 42 h after stimulation of gonadotropinreleasing hormone.KEY WORDS: estradiol-17β β β β , final oocyte maturation, gonadosomatic index, LHRHa, ovarian development, sevenband grouper.

This study examined the relationship between post-ovulation time and fertilization rate of artiˆcially inseminated eggs of sevenband grouper Epinephelus septemfasciatus. Ovulation was induced by cholesterol pellet implantation of LHRHa (50 mg/kg) and occurred between 36 and 54 hours. The fertilization rates of the eggs collected from elevenˆsh decreased with time after ovulation from 88.2 (0 h) to 28.9 (12 h). The hatching rates of the eggs collected from the elevenˆsh also decreased, and they were 68.2 (peak), 33.3 andˆnally 0.9 at 0, 6 and 12 hours after ovulation, respectively. These results suggest that artiˆcial fertilization of sevenband grouper must be carried out immediately after ovulation in order to obtain eggs of good quality.

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