Annual Variation in Spawning Season of the Brackish Water Bivalve, Corbicula japonica Prime in the Ishikari River

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Other Title
  • 石狩川産ヤマトシジミの産卵期の年変動
  • イシカリガワサン ヤマトシジミ ノ サンランキ ノ ネン ヘンドウ

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Abstract

Wild brackish water bivalves, Coybicula japonica, were collected from fixed stations in the Ishikari River from June to September in 2001-2005 to investigate the annual variation in the spawning season of this species. Shell length, total weight and soft part weight were measured and the ovarian maturity was examined by using the smear method. The earliest spawning from the ovarian observation was in late June 2004 and the latest spawning was in late August 2003, that is a 2-month difference in spawning season. The start of spawning corresponded to the water temperature of 21.5-23.5°C (mean 22.5±0.9°C) at fixed stations, suggesting that spawning starts at around 22.5°C. Early spawning or late spawning depends on the difference in time the water temperature reaches 22.5°C. The earliest active spawning started in early July 2004 and continued until early August, but the late active spawning started in late August 2003, 2005 and lasted until early September. The active spawning period was longer in 2004, when the spawning season was early and the water temperature rose suddenly to over 22.5°C and remained at the higher temperature for half a month, but was shorter in 2003, when the temperature rose slowly to 22.5°Cin the late spawning season. The longer active spawning season is presumed to be advantageous for recruitment, but not the shorter active spawning season.

Journal

  • Aquaculture Science

    Aquaculture Science 54 (3), 313-318, 2006

    Japanese Society for Aquaculture Science

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