Annual reproductive cycle of the greasyback shrimp Metapenaeus ensis in Ise Bay,Japan |
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Authors: | Yamane Fumihiro Suitoh Katsuyoshi Okumura Takuji Toyota Kenji Tsutsui Naoaki Ohira Tsuyoshi |
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Affiliation: | 1.Mie Prefectural Fish Farming Center, 3564-1 Hamajima, Shima, Mie, 517-0404, Japan ;2.Department of Marine Bioresources, Faculty of Bioresources, Mie University, Tsu, Mie, 514-8507, Japan ;3.Aichi Fish Farming Institute, Tahara, Aichi, 441-3618, Japan ;4.Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Minami-ise, Mie, 516-0193, Japan ;5.Department of Biological Sciences, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa, 259-1293, Japan ;6.Department of Biological Science and Technology, Faculty of Industrial Science and Technology, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo, 125-8585, Japan ;7.Marine Biological Station, Sado Center for Ecological Sustainability, Niigata University, Sado, Niigata, 952-2135, Japan ; |
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Abstract: | The greasyback shrimp Metapenaeus ensis is widely distributed along the coast of India and the West Pacific where it is an important fisheries species. We have examined seasonal changes in ovarian development, spermatogenesis, and mating of Me. ensis in histological studies and by external observations on specimens collected in Ise Bay, its northernmost habitat. Ovaries were found to be previtellogenic from February to May, with the first signs of development being the accumulation of yolk in oocytes in late May. Ovarian shadow ratios were high during the period late July to mid-September. The formation of cortical rods in the peripheries of oocytes and germinal vesicle breakdown were observed in ovaries from late June to September. Male shrimps had sperm in the testes during the period early June to early October, and female shrimps had spermatophores in spermatheca after early July. In late July, some post-spawn female shrimps had exogenous vitellogenic oocytes in their ovaries, indicating that ovarian development had been repeated in preparation for the next spawning. Ovarian shadow ratios, which were positively correlated with gonadosomatic indices and ovarian development, seem to be a useful marker to determine ovarian development. Our results indicate that mating in Me. ensis started in early July and that the spawning season ranged from July to September with more than two cycles of spawning in Ise Bay. |
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