Hypoxia is one of the major threats to biodiversity in aquatic systems. The association of hypoxia with nutrient-rich effluent input into aquatic systems results in scenarios where hypoxic waters could be contaminated with a wide range of chemicals, including metals. Despite this, little is known about the ability of fish to respond to hypoxia when exposures occur in the presence of environmental toxicants. We address this knowledge gap by investigating the effects of exposures to different levels of oxygen in the presence or absence of copper using the three-spined sticklebacks (Gasterosteus aculeatus) model. Fish were exposed to different air saturations (AS; 100%, 75% and 50%) in combination with copper (20 μg/L) over a 4 day period. The critical oxygen level (Pcrit), an indicator of acute hypoxia tolerance, was 54.64 ± 2.51% AS under control conditions, and 36.21 ± 2.14% when fish were chronically exposed to hypoxia (50% AS) for 4 days, revealing the ability of fish to acclimate to low oxygen conditions. Importantly, the additional exposure to copper (20 μg/L) prevented this improvement in Pcrit, impairing hypoxia acclimation. In addition, an increase in ventilation rate was observed for combined copper and hypoxia exposure, compared to the single stressors or the controls. Interestingly, in the groups exposed to copper, a large increase in variation in the measured Pcrit was observed between individuals, both under normoxic and hypoxic conditions. This variation, if observed in wild populations, may lead to selection for a tolerant phenotype and alterations in the gene pool of the populations, with consequences for their sustainability. Our findings provide strong evidence that copper reduces the capacity of fish to respond to hypoxia by preventing acclimation and will inform predictions of the consequences of global increases of hypoxia in water systems affected by other pollutants worldwide.

中文翻译：

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亚致死铜暴露抑制了模型鱼类适应缺氧的能力。

缺氧是对水生生物多样性的主要威胁之一。低氧与向水生系统输入的营养丰富的废水的关联会导致低氧水域可能被多种化学物质（包括金属）污染的情况。尽管如此，对于在环境毒物存在下发生暴露时鱼类对缺氧的反应能力知之甚少。我们通过使用三轴棘背back（Gasterosteus aculeatus）模型调查在有铜或无铜下暴露于不同水平的氧气所造成的影响，从而解决了这一知识鸿沟。在4天的时间内，将鱼与铜（20μg/ L）结合在一起暴露于不同的空气饱和度（AS; 100％，75％和50％）。临界氧水平（Pcrit）是急性低氧耐受性的指标，为54.64±2。对照条件下的AS为51％，长期缺氧（50％AS）的情况持续4天时为36.21±2.14％，这表明鱼具有适应低氧条件的能力。重要的是，额外的铜暴露（20μg/ L）阻止了Pcrit的这种改善，削弱了缺氧适应性。此外，与单一应激源或对照相比，铜和缺氧的联合暴露可观察到通气率增加。有趣的是，在常氧和低氧条件下，在暴露于铜的组中，观察到个体之间测得的Pcrit的变化大大增加。如果在野生种群中观察到这种变异，可能会导致选择耐受的表型和种群基因库发生变化，从而影响其可持续性。