ISSN : 1225-3480
The gametogenic cycle and the spawning season in female and male Cyclina sinensis were investigated by quantitative statistical analysis using an image analyzer system, and the biological minimum size (the size at 50% of sexual maturity) was calculated by combination of quantitative data by size and von Bertalanffy's equation. Compared the gametogenic cycle by quantitative statistical analysis with the previous qualitative results (Kim et al., 2000; Chung et al., 2003) in female and male C. sinensis, monthly changes in female and male gametogenic cycle calculated by quantitative statistical analysis showed similar patterns to the gonadal stages in female and male reproductive cycle by qualitative histological analysis. Comparisons of monthly changes in the portions (%) of each area to eight kinds of areas by quantitative statistical analysis in the gonads in female and male C. sinensis are as follows. Monthly changes in the portions (%) of the ovary areas to total tissue areas in females and also monthly changes in the portions of the testis areas to total tissue areas in males increased in March and reached the maximum in May, and then showed a rapid decrease from June to October. Monthly changes in the portions (%) of oocyte areas to ovarian tissue areas in females and also monthly changes in the portions of the areas of the spermatogenic stages to testis areas in males began to increase in March and reached the maximum in June in females and males, and then rapidly dropped from July to October in females and males when spawnig occurred. From these data, it is apparent that the number of spawning seasons in female and male C. sinensis occurred once per year, from July to October. Monthly changes in the number of the oocytes per mm2 and in the mean diameter of the oocyte in captured image which were calculated for each female slide showed a maximum in May and reached the minimum from December to February. Therefore, C. sinensis in both sexes showed a unimodal gametogenic cycle during the year. The percentage of sexual maturity of female and male clams ranging from 25.1 to 30.0 mm in length was over 50% and 100% for clams over 40.1 mm length. In this study, the biological minimum size (sexually mature shell lengths at 50% of sexual maturity) in females and males were 26.85 and 26.28 mm, respectively.
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