Annual reproductive cycle of the oyster, Saccostrea kegaki(Torigoe & Inaba 1981) on the southern coast of Jeju island, Korea

Abstract

Gametogenesis of the oyster Saccostrea kegaki (Torigoe & Inaba, 1981) on the southern coast of Jeju (Cheju) Island, Korea was assessed monthly (March 2001 to February 2002). Gametogenesis in females and males commenced in April when the water temperature reached 16.5 degrees C. Ripe gametes were observed from June to September in both sexes. Partially spawned oysters were evident from July to October when the water temperature ranged 24.6-26.7 degrees C. Most oysters collected in July and August exhibited partially empty follicles with large eggs (>35 mu m in diameter), suggesting that these two months are the major spawning periods. From November to March, most female oysters were in resting stage exhibiting no gametes in the follicles. In contrast, spawning or spent male oysters could be seen during November and January. Monthly mean oocyte diameters ranged from 10.3 +/- 1.7 mu m in April (early developing stage) to 36.9 +/- 5.7 mu m in August (ripe stage) and the mature oocyte was comparatively smaller than the size found in other oysters. The relatively slow rate of gametogenesis observed in S. kegaki off southern Jeju could be in part explained by low level of food in the water column rather than by water temperature.