The reproductive life-history of molluscs can be divided into gonochorism and hermaphroditism, while hermaphroditism is further classified into simultaneous (synchronous or functional) and sequential (asynchronous) (Heller 1993 Gosling 2004). Approximately 40% of the 5600 mollusc genera are either simultaneous or sequential hermaphrodites. Hermaphroditism occurs in 100% of the Solenogastres, 99% of the Opisthobranchia, 100% of the Pulmonata, 3% of the Prosobranchia and 9% of the Bivalvia. Simultaneous hermaphroditism is the simultaneous release of eggs and sperm by one organism during the same season. Sequential hermaphroditism is the function of an organism first as one sex, then as another (Heller 1993). This study investigated the sex of Manila clam, Ruditapes philippinarum by verifying changes in sex ratio (F:M) with size and sex reversal stages. Adult one-year-old (11 months; SL 36.75±3.0 mm) R. philippinarum were used for sex reversal identification. Each individual was tagged on its shell prior to being reared in the wild for reproductive analysis, and sex was confirmed using the germ cell aspiration (GCA) method. Sex ratio (F:M) at the commencement of the study (June 2009) was 1:1.23, but changed to 1:0.87 by the end (July 2010). Overall sex reversal rate was 19.0%. Specifically, male to female sex reversal ratio was 21.05%, which was higher than the female to male sex reversal ratio of 12.9%. Based on our results, R. philippinarum has been confirmed to possess a sequentially hermaphroditic life-history.

• Ji Seon Park(Department of Aqualife Medicine, Chonnam National University)
• Jung Sick Lee(Department of Aqualife Medicine, Chonnam National University)
• Yun Kyung Shin(Aquaculture Management Division)
• Jung Jun Park(Pathology Division, Aquaculture Research Institute, NFRDI)