Chlamys farreri (Jones et Preston, 1904)

Common name: Japanese scallop, Chinese scallop, Farrer's scallop, Akazara scallop

Ch. farreri is a Pacific Asian subtropical species (Fig. 6). In the Sea of Japan, it is widely distributed along the southern coasts, which is the northern border of its natural habitat. Also, it occurs at the Middle Primorye and at Japanese Island in total bathymetric range from 0.5 to 24 m (Scarlato, 1981). The mollusk mainly inhabits the gravel and pebbled grounds. Frequently scallops form many-tier reefs in rocks and oyster banks. Density of settlements can vary extremely up to 150-180 specimens�m^-2 (in reefs) in depth range of 1.5-2.5 m. On other depths their density decreases down to 5-10 specimens�m^-2. This species occurs at temperature range of near-bottom waters up to 19-22 �C, and salinity range of 32-34 �.

This species is an object for mariculture and fishery in East Asian countries (Wang, Shieh, 1991). In Russia, Japanese scallop is one of the most perspective species for fishery and mariculture (Bregman, 1982; Afreichuk, 1992a).

According to recent investigations (Afreichuk, 1992a), the population of Ch. farreri from Posjet Bay is represented by mollusks with shell height up to 112 mm, but individuals measuring 70-80 mm predominate. The maximum age of scallops is 9 years, but the population is mainly represented by mollusks of three (35 %) and four (27 %) years old at average 3.5 years old. After 6 years, natural elimination increased markedly. Therefore, only 12 % of population are older than 6 years old.

The most intensive linear growth is observed in the first three years and can amount up to 19 mm�yr^-1. At the age of 4-7, the shell grows by 5.8-11.5 mm�yr^-1. After this, linear growth decelerates markedly (Afreichuk, 1992b). The scallops reach marketable size (72 mm) in about 3-4 years. At that time the muscles weight 5.5 g. whenever the muscle weight of a 5-year-old scallop with average shell height of 90 mm is 11 g. In total muscles comprise 12-14 % of the total weight of the mollusk and the shells amount to 63 % (Afreichuk, 1990).

The age of sexual maturity is 2 years old where shell�s height is 40-45 mm (Table 2). The approximate sex ratio (male : female) in population is 1 to 1.36. At Posjet Bay spawning in population starts at the end of June when temperature of near-bottom waters approach to 16 �C. The mass spawning begins in the middle of July at temperature of 18-20 �C. Spawning ends at the end of August or early in September. Therefore the spawning period comprises 65 days (Afreichuk, 1992a).

Table 2. Shell height (mm) of differently ages Japanese scallop Chlamys farreri at southern part of the Sea of Japan (by Bregman, 1982), M� m

At Peter the Great Bay, larvae occur in plankton during the warmest season in July and August, at water temperature of 15-20 �C (Kas'yanov, et al., 1980). The maximum density of larvae occurs in shallower bights in bathymetric range of 5-7 m (Afreichuk et al., 1988). The period of settling on hard and fibrous substrate (depths up to 23 m) continues from the middle of July to early August. The optimal depth for spat collection is 5-8.5 meters (Gabaev, 1988). The density of juveniles' settlements at collectors can reach up to 229 at average 48 specimens�m^-2 (Afreichuk et al., 1988; Gabaev, 1990). The morphology of larvae and larval shell structure were described by V. A. Kulikova with co-authors (1981).

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