Time course of final oocyte maturation and ovulation in chub mackerel Scomber japonicus induced by hCG and GnRHa

Tetsuro Shiraishi, Suvarna D. Ketkar, Hajime Kitano, Mitsuo Nyuji, Akihiko Yamaguchi, Michiya Matsuyama

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25 Citations (Scopus)

Abstract

The question of whether the ovulation and spawning time in chub mackerel Scomber japonicus is entrained by a circadian rhythm was raised by our previous experiments. Further questions were also raised about whether the time course of human chorionic gonadotropin (hCG)-induced final oocyte maturation (FOM) and ovulation reflected the natural time course induced by endogeneous pituitary gonadotropin (GtH). To address these questions, hCG and gonadotropin-releasing hormone analog (GnRHa) were administered at two 'opposite' times, 14:00 and 02:00 hours, and the time courses of FOM and ovulation were compared. When hCG was injected, ovulation occurred 33 h post-injection in both groups, regardless of the timing of the hCG injection. The timing of ovulation in chub mackerel depends on the timing of hCG injection, but apparently not on circadian rhythms. When GnRHa was injected, ovulation began at 36 h post-injection of GnRHa, regardless of the timing of injection. These results indicate that the time course of FOM and ovulation in the chub mackerel followed a similar pattern whether stimulated by hCG injection or spontaneous luteinizing hormone (LH) surge because GnRHa induces the secretion of endogenous GtH (primarily LH) from the fish pituitary. Thus, it is concluded that the time course of hCG-induced FOM and ovulation in chub mackerel follows the natural time course induced by endogenous pituitary LH.

Original languageEnglish
Pages (from-to)764-769
Number of pages6
JournalFisheries science
Volume74
Issue number4
DOIs
Publication statusPublished - Aug 1 2008

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All Science Journal Classification (ASJC) codes

  • Aquatic Science

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