Quantification of reproductive effort of the triploid Pacific oyster, Crassostrea gigas raised in intertidal rack and bag oyster culture system off the west coast of Korea during spawning season

Oyster culture forms one of the major produce of aquaculture industry in Korea. Due to the demand for production, it is necessary to maintain a steady culture process. However, as a result of oil spill accident and other environmental problems in the west coast, there is a need to find a quick recovery in the production of oysters. While oyster culture in Korea is dominated by use of diploid oysters, an alternative to fast recovery for oyster industry is to introduce the use of triploid oysters. Triploid oysters have advantage in terms of faster growth and negligible quantity of reproductive effort during spawning, resulting in shorter grow-out period and improved meat quality compared to diploid oysters. In this study, we determined the reproductive effort in triploid females of Pacific oyster, Crassostrea gigas using an indirect enzyme-linked immunosorbent assay (ELISA). Two years old triploid and diploid female oysters raised in rack and bag oyster culture system on the west coast of Korea were collected during spawning and post-spawning season in 2013. Histology revealed that the diploid females spawned from June to September, with a peak in June. Unlike diploids, the triploid females exhibited no sign of spawning as the diploids were actively engaged in spawning. During post-spawning season, the triploid oysters reabsorbed the mature remnant eggs in their follicles. Gonad somatic index (GSI), determined using ELISA, of the diploid females reached its peak in June as 22.2%. In contrast, GSI of the triploids recorded during spawning peak was only 3.4%. Carbohydrate and glycogen contents in the triploid oyster tissues during spawning season were much higher than in diploids, suggesting that the triploids used minimum energy for reproduction in summer season, containing very small amount of gonad and high level of glycogen. Statement of relevance: Reproductive efforts (amount and number of eggs) of the diploid and triploid Pacific oysters measured in this study clearly demonstrated sterility of the triploid oysters during spawning season in summer. The present study also report gametogenic pattern of the triploid, crucial in the management of oyster aquaculture. (C) 2016 Elsevier B.V. All rights reserved.