Shell growth and age determination of the brackish water bivalve Corbicula japonica in Lake Shinji, Japan

摘要

Shell growth and age determination of Corbicula japonica were investigated from samples collected monthly at two sites and field growth experiments from November 1999 to November 2000 in Lake Shirji. Both specimens did not grow in winter when the water temperature was below 11degreesC, but grew rapidly from spring to early summer when the water temperature rose from 15degreesC to 30degreesC, before further growing slowly from summer to autumn after the main breeding period. The monthly marginal growth distribution of the samples indicated that the concentric groove on the shell surface was an annual growth ring. It is concluded that the age of C. japonica in the i-ring group when the shell growth resumed in spring was i + 0.5 (i = 1, 2,...), because the first true growth ring was formed at 0-2 mm in shell length, which then faded with growth. Lee's phenomenon was observed in the age determination results, and thus the growth coefficient and the asymptotic shell length of the von Eertelanffy growth equation were not estimated from the samples. However, these parameters were estimated from the annual shell length increments of the experimental individuals, which were 0.331/year and 28.2 mm, respectively. References: 29