Reproductive strategy of the tiny abyssal scallop (Delectopecten vitreus macrocheiricolus) collected on the bottom of the Japan Sea, surmised from histological observations of the gonads.

Two hundred and fifteen individuals of the tiny abyssal scallop (Delectopecten vitreus macrocheiricolus) were collected at a depth of around 3,000 m on the bottom of the Japan Sea during a cruise of the Yokosuka/Shinkai 6500 YK 01-06. The scallop population included specimens of 4 sizes, i.e., very small, small, middle, and large, with mantle sizes of 1-2mm, 3-5mm, 6-9mm, and 10-12mm, respectively. Histological observations revealed that the large-size group was at the stage just after oviposition or spermiation, or in the regressed stage of gametogenesis. The small- and middle-size groups were in the growing stage of gametogenesis. These results suggest that only the large-size individuals were responsible for reproduction and that the small- and middle-size individuals would participate in subsequent reproductions. This paper will discuss the reproductive strategy of this scallop living at such great depth.