International Research Center for Marine Biosciences, Ministry of Science and Technology, Shanghai Ocean University, Shanghai, 201306, China; Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Ministry of Education, Shanghai Ocean University, Shanghai, 201306, China.
Department of Marine Biology, Institute for Biological Sciences, University of Rostock, Rostock, Germany; Department of Maritime Systems, Interdisciplinary Faculty, University of Rostock, Rostock, Germany.
Mar Environ Res. 2022 Jul;179:105705. doi: 10.1016/j.marenvres.2022.105705. Epub 2022 Jul 16.
Intertidal and estuarine bivalves are adapted to fluctuating environmental conditions but the cellular adaptive mechanisms under combined stress scenarios are not well understood. The Hong Kong oysters Crassostrea hongkongensis experience periodic hypoxia/reoxygenation and salinity fluctuations during tidal cycles and extreme weather, which can negatively affect the respiratory organs (gills) involved in oxygen uptake and transport. We determined the effects of periodic hypoxia under different salinities on the oxidative stress response in Hong Kong oysters. Oxidative stress parameters (activities of superoxide dismutase (SOD), and catalase (CAT), tissue levels of malondialdehyde (MDA) and protein carbonyl content (PCC)) were determined in the gills of oysters exposed to diel-cycling hypoxia (hypoxia at night: 12h at 2 mg/L, reoxygenation: 12h at 6 mg/L) and normal dissolved oxygen (DO) (6 mg/L) under three salinities (10, 25, and 35‰) for 28 days. Oxygen regime in combination with salinity changes had significant interactive effects on all studied parameters except SOD. Salinity, DO and their interactions increased PCC after 14 and 28 days of exposure, and the combination of hypoxia/reoxygenation and decreased salinity showed the most severe effect. MDA content of the gills increased only after the long-term (28 days) exposure in decreased or increased salinity under normal DO treatments, showing PCC was more sensitive than MDA as biomarker of oxidative stress. Low salinity suppressed SOD activity regardless of the DO, whereas hypoxia induced SOD responses. CAT activities decreased significantly under high salinity with hypoxia/reoxygenation conditions. Our findings highlighted that periodic hypoxia/reoxygenation with salinity change induced antioxidant responses, which can impact the health of Hong Kong oyster C. hongkongensis and prolonged salinity stress may be one reason for the mortality during its aquaculture process.
潮间带和河口区双壳贝类能适应环境的波动，但对于联合胁迫下的细胞适应机制还不太了解。香港牡蛎（Crassostrea hongkongensis）在潮汐周期和极端天气下会经历周期性缺氧/复氧和盐度波动，这会对参与氧气摄取和运输的呼吸器官（鳃）产生负面影响。我们确定了不同盐度下周期性缺氧对香港牡蛎氧化应激反应的影响。在 28 天的时间里，我们在三种盐度（10、25 和 35‰）下，将暴露于昼夜循环缺氧（夜间缺氧 12 小时，氧浓度为 2mg/L，复氧 12 小时，氧浓度为 6mg/L）和正常溶解氧（DO，6mg/L）下的牡蛎鳃中的氧化应激参数（超氧化物歧化酶（SOD）和过氧化氢酶（CAT）的活性、丙二醛（MDA）的组织含量和蛋白质羰基含量（PCC））进行了测定。除了 SOD 之外，氧气处理与盐度变化的相互作用对所有研究参数都有显著影响。盐度、DO 及其相互作用增加了暴露 14 和 28 天后的 PCC，而缺氧/复氧与低盐度的组合表现出最严重的影响。在正常 DO 处理下，只有在低盐度或高盐度下长期（28 天）暴露后，鳃中的 MDA 含量才会增加，这表明 PCC 比 MDA 更敏感，是氧化应激的生物标志物。无论 DO 如何，低盐度都会抑制 SOD 活性，而缺氧会诱导 SOD 反应。CAT 活性在高盐度和缺氧/复氧条件下显著下降。我们的研究结果表明，周期性缺氧/复氧与盐度变化会诱导抗氧化反应，这可能会影响香港牡蛎的健康，而长期的盐度胁迫可能是其水产养殖过程中死亡率的原因之一。
