宍道湖のヤマトシジミ個体群の成長および着底稚貝

Abstract

Growth and settlement of Corbicula japonica were studied in 2 sites of Lake Shinji i.e. Tamayu and Hikawa from June 1992 to March 1994. Annual growth rings were observed on the external surface of the shell. According to the number of growth rings, there were 6-ring groups of C.japonica in Tamayu site. In Hikawa site, 3-ring groups were observed where 0-ring group was dominant among the groups. The mean shell length of each ring group was higher at Hikawa site compared to Tamayu site. Shell growth was high from spring to autumn, and very low during winter. Growth pattern in soft tissue differed between 1-ring group and 2 or 3-ring groups. The latter groups decreased their weight from June to September 1992. Settled juveniles appeared throughout the year. The density of juveniles was high from spring to autumn, and very low in winter. Many C.japonica juveniles settled in each site, but reduction level of post-settled juveniles was higher at Hikawa site than Tamayu site.