1. Climate change has emerged as an increasingly important threat to freshwater systems. To cope with rapidly changing thermal regimes, freshwater fishes must either relocate or adjust through genetic adaptation and/or phenotypic plasticity. Short-term responses to elevated water temperature have been well studied in freshwater fishes; however, far less is understood about change induced by long-term exposure. Furthermore, few studies have investigated the effects of temperature on already imperilled species, which may be more sensitive to environmental change.
2. This study investigated the effects of rearing temperature on critical thermal maximum (CT_max), agitation temperature (T_ag, temperature at which fish show behavioural signs of thermal stress) and gill size in pugnose shiner, Notropis anogenus, a threatened species in Canada. Juvenile pugnose shiner were reared for 4 months across five different ecologically relevant temperatures. CT_max and T_ag were measured under normoxia and acute exposure to hypoxia to test for oxygen sensitivity of the upper thermal limits in this species.
3. CT_max increased with elevated water temperature. T_ag also increased with rearing temperature and occurred, on average, 4.3°C above acclimation temperatures. The CT_max and T_ag were lower when fish were exposed acutely to hypoxia. Interestingly, gill size (e.g. total gill filament length) increased with rearing temperature, which may increase oxygen uptake capacity and support increased metabolic demands of warmer waters.
4. Overall, pugnose shiner show plasticity in several traits in response to long-term exposure to elevated water temperature that may facilitate persistence in warmer waters. However, acute hypoxia exposure reduced thermal tolerance, stressing the importance of evaluating interactive effects of multiple stressors.
5. Identifying source populations of pugnose shiner with greater thermal tolerance or implementing captive breeding under higher temperature regimes may improve the success of re-introduction efforts in the face of climate change, but the consequences to fitness of increased thermal tolerance should be examined.

中文翻译：

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应对气候变化：濒危淡水鱼对水温升高的表型可塑性

1. 气候变化已成为对淡水系统日益重要的威胁。为了应对快速变化的热状况，淡水鱼必须通过遗传适应和/或表型可塑性重新定位或调整。淡水鱼对水温升高的短期反应已经得到很好的研究。然而，人们对长期暴露引起的变化了解甚少。此外，很少有研究调查温度对已经濒临灭绝的物种的影响，这些物种可能对环境变化更敏感。
2. 这项研究调查了临界温度最高（CT饲养温度的影响_最大），搅拌温度（牛逼_AG，温度在其中的鱼表明热应力的行为体征），并在pugnose夏纳鳃大小，美洲鱥属anogenus，在加拿大的一个濒危物种。幼鱼在五种不同的生态相关温度下饲养了 4 个月。CT _max和T _ag在常氧和急性缺氧条件下测量，以测试该物种热极限的氧敏感性。
3. CT _max随水温升高而增加。Ť _AG还与饲养温度增加和发生，平均来说，4.3A℃的上述驯化温度。当鱼急性暴露于缺氧时，CT _max和T _ag较低。有趣的是，鳃尺寸（例如总鳃丝长度）随着饲养温度的增加而增加，这可能会增加摄氧量并支持较温暖水域增加的代谢需求。
4. 总体而言，由于长期暴露在升高的水温下，pugnose Shiner 在几个性状中表现出可塑性，这可能有助于在较温暖的水域中持续存在。然而，急性缺氧暴露降低了热耐受性，强调了评估多种压力源相互作用的重要性。
5. 确定具有更高耐热性的美洲虎的来源种群或在较高温度条件下实施圈养繁殖可能会提高面对气候变化重新引入工作的成功率，但应检查提高耐热性对适应度的影响。