Seasonal Changes in Reproductive Condition of The Pacific Oysters, Crassostrea gigas(Thunberg) from Suspended Culture in Gosung Bay, Korea
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Seasonal variation in reproductive condition of the Pacific oyster, Crassostrea gigas was investigated from a suspended cultured oyster population in Gosung Bay, South Korea using histological techniques. Gametogenesis of oysters initiated in February when water temperature reached 11 to 13oC. Increase in oocyte size and the number resulting in follicle expansions was observed from March to May. First spawning of oysters observed in mid June when the surface water temperature reached 22 to 25oC. Spawning activity of oysters extended from mid June to late September with two marked spawning peaks in June and August. Most oysters collected from October to December exhibited few residual eggs in packed follicles exhibiting a typical spent condition. No gametes were observed from December to February from oysters collected in the Bay. Gonadal development of oysters in the Bay seemed to follow a seasonal fluctuation in environmental conditions such as water temperature and food availability in the water column. Spawning of oysters in late June was in part associated with sudden drop in salinity due to vast amount of freshwater input in the Bay after summer flooding. Sex ratio of oysters was 59.5% male and 39.8% female. Less than 1 percent (0.6%) of the oysters examined were hermaphrodite; few eggs were observed in testis.
Abstract
Seasonal variation in reproductive condition of the Pacific oyster, Crassostrea gigas was investigated from a suspended cultured oyster population in Gosung Bay, South Korea using histological techniques. Gametogenesis of oysters initiated in February when water temperature reached 11 to 13oC. Increase in oocyte size and the number resulting in follicle expansions was observed from March to May. First spawning of oysters observed in mid June when the surface water temperature reached 22 to 25oC. Spawning activity of oysters extended from mid June to late September with two marked spawning peaks in June and August. Most oysters collected from October to December exhibited few residual eggs in packed follicles exhibiting a typical spent condition. No gametes were observed from December to February from oysters collected in the Bay. Gonadal development of oysters in the Bay seemed to follow a seasonal fluctuation in environmental conditions such as water temperature and food availability in the water column. Spawning of oysters in late June was in part associated with sudden drop in salinity due to vast amount of freshwater input in the Bay after summer flooding. Sex ratio of oysters was 59.5% male and 39.8% female. Less than 1 percent (0.6%) of the oysters examined were hermaphrodite; few eggs were observed in testis.