Physiological features of species can determine the resilience and adaptation of organisms to the environment. Swimming capacity and metabolic traits are key factors for fish survival, mating and predator–prey interactions. Individuals of the same species can display high phenotypic variation often in response to varying environmental conditions. We investigated the effects of captive breeding conditions on swimming capacity, metabolic traits and morphology by comparing a captive population with a wild population of the endangered Spanish toothcarp (Aphanius iberus). We measured swimming capabilities and oxygen‐uptake rates simultaneously, the latter as a proxy for metabolic rate, using a swim tunnel respirometer. Results showed significant differences in standard metabolic rate (SMR), maximum metabolic rate (MMR) and absolute aerobic scope (AAS) between populations, as well as differences in morphological features between populations and sexes. In contrast, we did not find significant differences in critical swimming speed between populations or sexes. Differences in SMR between sexes were found in the captive population, and males showed nearly a twofold increase in SMR when compared with females. SMR, MMR and AAS were, on average, twofold lower for the captive population in comparison with the wild population. These differences in metabolic traits likely reflected captivity conditions, which were low food availability and the absence of predators, which in turn, may have influenced morphological traits, such as body and caudal peduncle shape and head size. At the same time, morphological traits also influenced metabolic traits of the populations. The lower SMR and MMR of captive individuals may be related to their deeper body shapes. Taken together, our results suggested that captive breeding conditions caused significant physiological and morphological changes in the endangered Spanish toothcarp. Reduced metabolic traits and changes in morphology may affect fitness‐related traits of the captive populations once reintroduced into the wild, thereby compromising conservation efforts. We therefore recommend to experimentally testing for the effects and consequences of captive breeding conditions before fish are released into the wild for successful conservation of them and other endangered species.

中文翻译：

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圈养繁殖条件降低了濒临灭绝的西班牙牙果Aphanius iberus的代谢率并改变其形态性状

物种的生理特征可以决定生物体对环境的适应力和适应性。游泳能力和代谢特征是鱼类存活，交配和食肉动物与猎物相互作用的关键因素。同一物种的个体通常可以响应于变化的环境条件而表现出高表型变异。我们通过比较圈养种群与濒危西班牙牙果（Aphanius iberus）的野生种群，研究了圈养繁殖条件对游泳能力，代谢性状和形态的影响）。我们使用游泳隧道呼吸仪同时测量了游泳能力和摄氧率，后者是代谢率的替代指标。结果显示，人群之间的标准代谢率（SMR），最大代谢率（MMR）和绝对有氧运动范围（AAS）存在显着差异，并且人群与性别之间的形态特征也存在差异。相比之下，我们在人群或性别之间的关键游泳速度上没有发现显着差异。在圈养人群中发现性别之间的SMR差异，男性与女性相比，SMR增加了近两倍。与野生种群相比，圈养种群的SMR，MMR和AAS平均要低两倍。这些代谢性状的差异可能反映了人工饲养条件，它们的食物供应量低，没有肉食动物，这反过来可能会影响形态特征，例如身体和尾柄的形状和头部大小。同时，形态特征也影响种群的代谢特征。圈养个体的较低SMR和MMR可能与他们较深的身体形状有关。两者合计，我们的结果表明，圈养繁殖条件导致了濒临灭绝的西班牙牙果的重大生理和形态变化。一旦重新引入野外，减少的代谢性状和形态变化可能会影响圈养种群的适应性相关性状，从而损害保护工作。