Key Laboratory of Biodiversity of Aquatic Organisms, College of Life Science and Technology, Harbin Normal University, Harbin, 150025, China.
Fish Physiol Biochem. 2021 Aug;47(4):919-938. doi: 10.1007/s10695-021-00947-4. Epub 2021 Apr 16.
Hypoxia is one of the most significant threats to biodiversity in aquatic systems. The ability of high-latitude fish to tolerate hypoxia with histological and physiological responses is mostly unknown. We address this knowledge gap by investigating the effects of exposures to different oxygen levels using Phoxinus lagowskii (a high-latitude, cold-water fish) as a model. Fish were exposed to different oxygen levels (0.5 mg/L and 3 mg/L) for 24 h. The loss of equilibrium (LOE), an indicator of acute hypoxia tolerance, was 0.21 ± 0.01 mg/L, revealing the ability of fish to tolerate low-oxygen conditions. We sought to determine if, in P. lagowskii, the histology of gills and liver, blood indicators, enzyme activities of carbohydrate and lipid metabolism, and antioxidants changed to relieve stress in response to acute hypoxia. Notably, changes in vigorous jumping behavior under low oxygen revealed the exceptional hypoxia acclimation response compared with other low-latitude fish. A decrease in blood parameters, including RBC, WBC, and Hb, as well as an increase in MCV was observed compared to the controls. The increased total area in lamella and decreased ILCM volume in P. lagowskii gills were detected in the present study. Our results also showed the size of vacuoles in the livers of the hypoxic fish shrunk. Interestingly, an increase in the enzyme activity of lipid metabolism but not glucose metabolism was observed in the groups exposed to hypoxia at 6 h and 24 h. After combining histology and physiology results, our findings provide evidence that lipid metabolism plays a crucial role in enhancing hypoxia acclimation in P. lagowskii. Additionally, SOD activity significantly increased during hypoxia, suggesting the presence of an antioxidant response of P. lagowskii during hypoxia. High expression levels of lipogenesis and lipolysis-related genes were detected in the 6 h 3 mg/L and 24 h 3 mg/L hypoxia group. Enhanced expression of lipid-metabolism genes (ALS4, PGC-1, and FASN) was detected during hypoxia exposure. Together, these data suggest that P. lagowskii's ability to tolerate hypoxic events is likely mediated by a comprehensive strategy.
缺氧是水生系统生物多样性面临的最大威胁之一。高纬度鱼类通过组织学和生理学反应来耐受缺氧的能力在很大程度上尚不清楚。我们使用 Phoxinus lagowskii（一种高纬度冷水鱼类）作为模型，通过研究不同氧气水平暴露对其的影响来填补这一知识空白。鱼在不同氧气水平（0.5 mg/L 和 3 mg/L）下暴露 24 小时。平衡丧失（LOE），作为急性缺氧耐受性的指标，为 0.21±0.01mg/L，表明鱼类能够耐受低氧条件。我们试图确定 Phoxinus lagowskii 的鳃和肝脏组织学、血液指标、碳水化合物和脂质代谢酶活性以及抗氧化剂是否会发生变化，以缓解急性缺氧引起的应激。值得注意的是，与其他低纬度鱼类相比，低氧条件下剧烈跳跃行为的变化表明其具有非凡的低氧适应反应。与对照组相比，观察到血液参数（包括 RBC、WBC 和 Hb）下降，MCV 增加。在 Phoxinus lagowskii 鳃中，发现总鳃片面积增加，ILCM 体积减少。本研究还检测到缺氧鱼肝脏中液泡的大小缩小。有趣的是，在 6 小时和 24 小时暴露于缺氧条件下，观察到脂质代谢酶活性增加，但葡萄糖代谢酶活性没有增加。将组织学和生理学结果结合起来，我们的发现表明脂质代谢在增强 Phoxinus lagowskii 的低氧适应中起着关键作用。此外，SOD 活性在缺氧期间显著增加，表明 Phoxinus lagowskii 在缺氧期间存在抗氧化反应。在 6 小时 3mg/L 和 24 小时 3mg/L 缺氧组中，检测到与脂肪生成和脂肪分解相关基因的高表达水平。在缺氧暴露期间，脂质代谢基因（ALS4、PGC-1 和 FASN）的表达增强。总之，这些数据表明，Phoxinus lagowskii 耐受缺氧事件的能力可能是通过一种综合策略介导的。
