Ultastructural studies of the development and degeneration of the oocytes and follicle cells in female Chlamys (Azumapecten) farreri farreri (Jones & Preston, 1904) are described for scallops collected from Daehuksando, Jeollanam-do, Korea. Vitellogenesis occurred by way of endogenous autosynthesis and exogenous heterosynthesis. Autosynthesis involved the combined activity of the Golgi complex, mitochondria, and rough endoplasmic reticulum, whereas heterosynthesis involved endocytotic incorporation of extraovarian precursors at the basal region of the early vitellogenic oocytes prior to the formation of the vitelline coat. Auxiliary cells were involved in the development of the previtellogenic and early vitellogenic oocytes and appear to play an integral role in vitellogenesis and oocyte degeneration by assimilating products originating from the degenerated oocytes, thus allowed the transfer of yolk precursors needed for vitellogenesis. Auxiliary cells presumably have a lysosomal system for breakdown products of oocyte degeneration. The reproductive cycle in females was classified into five stages: Stage I: early active stage (January to March), Stage 11: late active stage (March to April), Stage III: ripe stage (April to August), Stage IV: partially spawned stage (June to August), and Stage V: spent/inactive stage (August to January). The spawning period continued from June to August, with a peak between July and August when the seawater temperature was exceeded 22 degrees C. The percentage of first sexual maturity was 59.3% in individuals of 50.1-60.0 mm in shell height, and 100% in those > 70.1 mm in shell height. Because harvesting clams less than 50.1 mm in shell height could potentially cause a drastic reduction in recruitment, a measure indicating a prohibitory fishing size should be enacted for adequate fisheries management.
