Human activities present aquatic species with numerous of environmental challenges, including excessive nutrient pollution (nitrate) and altered pH regimes (freshwater acidification). In isolation, elevated nitrate and acidic pH can lower the blood oxygen-carrying capacity of aquatic species and cause corresponding declines in key functional performance traits such as growth and locomotor capacity. These factors may pose considerable physiological challenges to organisms but little is known about their combined effects. To characterise the energetic and physiological consequences of simultaneous exposure to nitrate and low pH, we exposed spangled perch (Leiopotherapon unicolor) to a combination of nitrate (0, 50 or 100 mg L-1) and pH (pH 7.0 or 4.0) treatments in a factorial experimental design. Blood oxygen-carrying capacity (haemoglobin concentration, methaemoglobin concentrations and oxygen equilibrium curves), aerobic scope and functional performance traits (growth, swimming performance and post-exercise recovery) were assessed after 28 days of exposure. The oxygen-carrying capacity of fish exposed to elevated nitrate (50 and 100 mg L-1) was compromised due to reductions in haematocrit, functional haemoglobin levels and a 3-fold increase in methaemoglobin concentrations. Oxygen uptake was also impeded due to a right shift in oxygen-haemoglobin binding curves of fish exposed to nitrate and pH 4.0 simultaneously. A reduced blood oxygen-carrying capacity translated to a lowered aerobic scope, and the functional performance of fish (growth and swimming performance and increased post-exercise recovery times) was compromised by the combined effects of nitrate and low pH. These results highlight the impacts on aquatic organisms living in environments threatened by excessive nitrate and acidic pH conditions.

中文翻译：

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同时暴露于硝酸盐和低pH值会降低淡水鱼的血液携氧能力和功能性能。

人类活动给水生物种带来了许多环境挑战，包括过度的营养物污染（硝酸盐）和改变的pH值制度（淡水酸化）。孤立地，升高的硝酸盐和酸性pH会降低水生物种的血液携氧能力，并导致诸如生长和运动能力等关键功能性能特征相应下降。这些因素可能会对生物体构成相当大的生理挑战，但对其综合作用知之甚少。为了表征同时暴露于硝酸盐和低pH值时的能量和生理后果，我们在以下条件下将亮点鲈鱼（单色Leiopotherapon）暴露于硝酸盐（0、50或100 mg L-1）和pH（pH 7.0或4.0）的组合处理中。析因实验设计。暴露28天后，评估了血液的载氧能力（血红蛋白浓度，血红蛋白浓度和氧平衡曲线），有氧范围和功能表现特征（生长，游泳表现和运动后恢复）。暴露于高浓度硝酸盐（50和100 mg L-1）的鱼的携氧能力受到了影响，这是因为血细胞比容降低，功能性血红蛋白水平降低以及血红蛋白浓度增加了3倍。由于同时暴露于硝酸盐和pH 4.0的鱼的氧-血红蛋白结合曲线发生了右移，因此也阻碍了氧的吸收。血液携氧能力降低导致有氧运动范围降低，硝酸盐和低pH值的共同作用损害了鱼的功能性能（生长和游泳性能以及增加的运动后恢复时间）。这些结果突显了对生活在硝酸盐和酸性pH值过高威胁环境中的水生生物的影响。