LIU Ranyang, GAO Lei, ZHANG Xingzhi, YANG Wenwen, ZHAO Junyan, ZHAO Bao, YU Haijie, XU Jixiang, LIU Lu, PENG Jinxia, WANG Lingling, SONG Linsheng
To elucidate the impacts of water environment of Dafeng River in Beihai, Guangxi, on health status of Hong Kong oyster(Crassostrea hongkongensis) cultured therein, the physicochemical factors in water quality, planktonic microalgae, bacterial abundance, and energy reserve and oxidative stress of Hong Kong oysters were surveyed in the main Hong Kong oyster farming area of Beihai Sea of Guangzhou, the mouth of the Dafeng River and the upper waters(108°52′49″E, 21°38′26″N; 108°51′30″E, 21°46′22″N) in September and October 2023. The results showed that, the estuarine water temperature was 28.1 ℃, with a salinity of 20.89, total bacterial abundance of 7.22×108 cells/L and Vibrio abundance of 1.49×107 cells/L in September. Diatom abundance was found to be approximately 1.3×107 cells/L, with the dominant species of Skeletonema costatum. The malondialdehyde (MDA) content of 9.60 nmol/mg protein was observed in the gill of cultivated Hong Kong oysters, with glycogen content of 6.18 mg/g and glucose content of 2.59 μmol/g in the adductor muscle. In October,however, the estuarine water temperature was decreased to 25.7 ℃, accompanied by an increase in salinity to 25.50, with bacterial abundance decreased to 4.97×107 cells/L and Vibrio abundance to 1.40×104 cells/L and diatom abundance decreased to 4.3×105 cells/L in the water. MDA content was 1.02 nmol/mg protein in the gill of cultivated Hong Kong oyster, and glycogen and glucose content in the adductor muscle was decreased to 2.49 mg/g and 1.94 μmol/g, respectively. The water temperature and total bacterial abundance were similar to those in the estuarine waters in the upstream waters in October. However, salinity and Vibrio abundance were relatively low, with high diatom abundance. The glycogen and glucose contents in adductor muscle were increased in cultivated Hong Kong oysters. In summary, Hong Kong oysters cultured in the Dafeng River estuary faced multiple environmental stressors, including high temperature, elevated bacterial and Vibrio abundances in September, leading to increased oxidative stress. In October, these oysters primarily encountered a single environmental pressure, high salinity, and improved oxidative stress status. The decrease in algal food led to decline in glycogen content and resistance to environmental changes in October, and there were lower salinity, higher diatom abundance, and relatively healthier conditions for Hong Kong oyster cultivation in upstream waters in the Dafeng River.
