The Annual Reproductive Cycle and Reproductive Effort of the Pacific Oyster Crassostrea gigas from a Tidal Flat in Incheon Bay on the West Coast of Korea

Understanding temporal changes in reproductive conditions and physicochemical environmental factors governing the variation is vital in the management and ecology of oysters. This study investigated the annual gametogenesis and reproductive effort of the Pacific oyster Crassostrea gigas in Incheon Bay using histology and indirect enzyme-linked immunoassay (ELISA). Seasonal changes in the reproductive condition were closely associated with the changes in sea surface temperature (SST), as a rapid increase in SST from April (10.1 °C) to early June (18.7 °C) coincided with the growth and maturation of the eggs. Histology indicated that the spawning was synchronous, as both males and females initiated the spawning in late June, which continued until early August. Gonad-somatic index (GSI), a ratio of the egg mass to the tissue weight determined by ELISA, showed a dramatic decline from late June (47.3%) to August (3.9%), suggesting that the females discharged a substantial amount of eggs through spawning, which accounted for approximately 40% of the body weight. The condition index (CI) of oysters determined in this study was comparable to those of oysters reported from the south coast, where oysters were raised in subtidal using suspended long lines, suggesting that the off-bottom culture of the Pacific oysters near the low tide line in Incheon Bay is a promising culture technique in the tidal flat environment.