Hypoxia is an increasing threat to aquatic ecosystems and its impact on economically and ecologically important marine fish species needs to be studied. Especially, the consequences of hypoxia when occurring along with harmful algal blooms (HABs) are currently not well documented. In this study, we investigated the effect of constant and intermittent (daily and weekly) hypoxia on respiration, immunity, hematological parameters, and oxidative status of red seabream for 2, 4, and 6 weeks. Under constant and daily intermittent hypoxia, respiration rate significantly increased in 2 weeks compared to the control. Constant and daily intermittent hypoxia caused significant decreases in the activity of alternative complement pathway, lysozyme, and the level of total immunoglobulin (Ig), as well as significant increases in the concentrations of cortisol, hemoglobin, red blood cells, and white blood cells. A significantly higher level of malondialdehyde was measured for all hypoxia-exposed groups, indicating lipid peroxidation and oxidative stress. At 4 and 6 week, the level of glutathione and enzymatic activities of glutathione reductase and glutathione peroxidase were significantly decreased after constant and daily intermittent hypoxia challenge. The enzymatic activities of superoxide dismutase and catalase were significantly increased at 2 and 4 weeks, but they were decreased after 6 weeks by constant and daily intermittent hypoxia. Constant and daily intermittent hypoxia with subsequent non-toxin producing dinoflagellate Cochlodinium polykrikoides treatment significantly reduced the respiration rate in 3 and 24 h exposure and survival rate of red seabream. Taken together, the red seabream can be vulnerable to HABs under hypoxia condition through inhibition of immunity and antioxidant defense ability. Our findings are helpful in better understanding of molecular and physiological effects of hypoxia, which can be used in aquaculture and fisheries management.

缺氧对水生生态系统的威胁日益增加，需要研究其对经济和生态上重要的海洋鱼类的影响。特别是，目前尚无充分证据证明缺氧与有害藻华（HAB）一起发生的后果。在这项研究中，我们调查了连续，间歇（每天和每周）缺氧对红鲷鱼的呼吸，免疫，血液学参数和氧化状态的影响，持续了2、4和6周。在恒定和每日间歇性缺氧下，与对照组相比，呼吸速率在2周内显着增加。持续和每日间歇性缺氧会导致替代补体途径，溶菌酶和总免疫球蛋白（Ig）的水平显着下降，皮质醇浓度显着升高，血红蛋白，红细胞和白细胞。所有低氧暴露组的丙二醛水平均明显升高，表明脂质过氧化和氧化应激。在连续和每日间歇性缺氧刺激后，第4周和第6周，谷胱甘肽水平和谷胱甘肽还原酶和谷胱甘肽过氧化物酶的酶活性显着降低。超氧化物歧化酶和过氧化氢酶的酶活性在第2周和第4周显着增加，但在6周后由于持续和每日间歇性缺氧而降低。持续和每日间歇性缺氧，随后产生非毒素的鞭毛藻 表明脂质过氧化和氧化应激。在连续和每日间歇性缺氧刺激后，第4周和第6周，谷胱甘肽水平和谷胱甘肽还原酶和谷胱甘肽过氧化物酶的酶活性显着降低。超氧化物歧化酶和过氧化氢酶的酶活性在第2周和第4周显着增加，但在6周后由于持续和每日间歇性缺氧而降低。持续和每日间歇性缺氧，随后产生非毒素的鞭毛藻 表明脂质过氧化和氧化应激。在连续和每日间歇性缺氧刺激后，第4周和第6周，谷胱甘肽水平和谷胱甘肽还原酶和谷胱甘肽过氧化物酶的酶活性显着降低。超氧化物歧化酶和过氧化氢酶的酶活性在第2周和第4周显着增加，但在6周后由于持续和每日间歇性缺氧而降低。持续和每日间歇性缺氧，随后产生非毒素的鞭毛藻 超氧化物歧化酶和过氧化氢酶的酶活性在第2周和第4周显着增加，但在6周后由于持续和每日间歇性缺氧而降低。持续和每日间歇性缺氧，随后产生非毒素的鞭毛藻 超氧化物歧化酶和过氧化氢酶的酶活性在第2周和第4周显着增加，但在6周后由于持续和每日间歇性缺氧而降低。持续和每日间歇性缺氧，随后产生非毒素的鞭毛藻Cochlodinium polykrikoides处理可显着降低暴露3和24 h的呼吸速率以及红鲷的存活率。总之，在低氧条件下，红鲷鱼可能会通过抑制免疫力和抗氧化防御能力而受到HAB的影响。我们的发现有助于更好地了解缺氧的分子和生理效应，可将其用于水产养殖和渔业管理。