Urbanization tends to increase water temperatures in streams and rivers and is hypothesized to be contributing to declines of many freshwater fishes. However, factors that influence individual variation in thermal tolerance, and how these may change seasonally, are not well understood. To address this knowledge gap, we studied redside dace Clinostomus elongatus, an imperilled stream fish native to rapidly urbanizing areas of eastern North America. In wild redside dace from rural Ohio, USA, acute upper thermal tolerance (i.e. critical thermal maximum, CTmax) ranged between ~34°C in summer (stream temperature ~22°C) and 27°C in winter (stream temperature ~2°C). Juveniles had higher CTmax than adults in spring and summer, but in winter, CTmax was higher in adults. Thermal safety margins (CTmax - ambient water temperature; ~11°C) were less than the increases in peak water temperature predicted for many redside dace streams due to the combined effects of climate change and urbanization. Furthermore, behavioural agitation occurred 5-6°C below CTmax. Safety margins were larger (>20°C) in autumn and winter. In addition, redside dace were more sensitive (2.5°C lower CTmax) than southern redbelly dace Chrosomus erythrogaster, a non-imperilled sympatric cyprinid. Body condition (Fulton's K) of adult redside dace was positively correlated with CTmax, but in juveniles, this relationship was significant only in one of two summers of experiments. Next, we measured CTmax of captive redside dace fed experimentally manipulated diets. In adults, but not juveniles, CTmax was higher in fish fed a high- vs. low-ration diet, indicating a causal link between nutrition and thermal tolerance. We conclude that redside dace will be challenged by predicted future summer temperatures, especially in urbanized habitats. Thus, habitat restoration that mitigates temperature increases is likely to benefit redside dace. We also suggest habitat restoration that improves food availability may increase thermal tolerance, and thus population resilience.

中文翻译：

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热耐受性取决于受鞭打的红边da Clinostomus elongatus的季节，年龄和身体状况。

城市化趋向于增加溪流和河流中的水温，并且据推测会导致许多淡水鱼类的减少。但是，影响热耐受性个体差异以及这些因子如何随季节变化的因素尚不十分清楚。为了解决这一知识鸿沟，我们研究了红边da鱼Clinostomus elongatus，一种濒临灭绝的溪流鱼类，原产于北美东部快速城市化地区。在来自美国俄亥俄州农村的野生红边ce中，急性最高热耐受性（即临界热最大值，CTmax）在夏季（河流温度〜22°C）〜34°C和冬季（河流温度〜2°C）的27°C之间。 C）。在春季和夏季，青少年的CTmax高于成年人，但在冬季，成年人的CTmax更高。热安全裕度（CTmax-环境水温；由于气候变化和城市化的综合影响，约11°C）低于许多红边da流所预测的最高水温升高。此外，行为搅动发生在CTmax以下5-6°C。在秋季和冬季，安全边际较大（> 20°C）。此外，红边da鱼比南方红腹sym鱼Chrosomus erythrogaster（一种不受干扰的同胞塞浦路斯）更敏感（CTmax降低2.5°C）。成年红边蕾丝的身体状况（富尔顿K）与CTmax呈正相关，但在青少年中，这种关系仅在两个夏天的实验之一中才有意义。接下来，我们测量了通过实验操作饮食喂养的圈养红边da的CTmax。在成年动物中，而不是未成年动物中，高饮食和低饮食的鱼的CTmax较高，表明营养与耐热性之间存在因果关系。我们得出的结论是，未来的夏季气温，尤其是在城市化的栖息地中，未来的夏季气温将对红边蕾丝构成挑战。因此，减轻温度升高的栖息地恢复很可能有益于红边da。我们还建议改善食物供应的栖息地恢复可能会提高耐热性，从而提高种群的适应能力。