Reproductive cycle of the venerid clam <Emphasis Type="Italic">Meretrix lusoria</Emphasis> in Ariake Sound and Tokyo Bay,Japan |
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Authors: | Yasuo Nakamura Tadashi Nakano Tatsuya Yurimoto Yukio Maeno Takayoshi Koizumi Akio Tamaki |
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Institution: | (1) National Institute for Environmental Studies, Tsukuba Ibaraki, 305-8506, Japan;(2) Graduate School of Science and Technology, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan;(3) Seikai National Fisheries Research Institute, 1551-8 Taira-machi, Nagasaki 851-2213, Japan;(4) Nihon Mikuniya Co., 3-45-10 Mizonokuchi, Takatsu, Kawasaki Kanagawa, 213-0001, Japan;(5) Faculty of Fisheries, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan |
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Abstract: | We assessed the reproductive cycle of the venerid clam Meretrix lusoria by histological analysis of the gonads. Individuals for study were collected from natural populations on the Shirakawa tidal
flat, Ariake Sound, and from populations that had been transplanted from the Shirakawa flat to the Oi flat in Tokyo Bay. In
both study areas, the reproductive cycle was synchronized between sexes. Gonads of the clam started to develop in early spring
and matured during the summer. Mass spawning occurred in the late summer/early fall. The clam matured at a shell length of
17–20 mm, which is much smaller than previously considered. While trophic conditions and salinity differed considerably in
the two study areas, water temperatures showed similar seasonal changes (12°C during the winter and around 30°C during the
summer). Thus, temperature probably controlled gonadal development. The coincidence of the period of spawning with the period
of frequent intrusion of hypoxic waters into the tidal flats in Tokyo Bay suggests that such hypoxic events interfere with
clam recruitment and are at least partly responsible for the disappearance of the natural population at this location. |
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