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

概要

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Wild brackish water bivalves, Corbicula japonica, were collected weekly from the Ishikari River (salinity 0.2-1.4 psu) from July to September in 2001 to discover the spawning season of this species. Two other C. japonica specimens, a wild bivalve from the Ishikari River and an introduced seed-bivalve inhabiting Lake Abashiri which were reared in a tank adjusted to salinity 5 psu were also sampled in the same period. All specimens were measured and the ovarian maturity was examined by using the smear method. The soft part index (soft part weight × 100 / total weight) and ovarian observations indicated that spawning of wild bivalves and reared wild bivalves was from late July to early September. Spawning of the reared seed-bivalve was from late August to early September. Thus, spawning of C. japonica in the Ishikari River is from late July to early September. During the spawning season, unspawned degenerated eggs were observed frequently, which seemed to be because of the unfavorable spawning conditions caused by low water temperature and the inherent low salinity in the summer of 2001. Spawning in the river is presumed to take place under extreme conditions, especially at low salinity.
日本水産増殖学会の論文