Swimming performance is a key feature that mediates fitness and survival in many fish species. Using a swim tunnel respirometer, we compared prolonged swimming performance and energy use for two competing species: an endangered, endemic toothcarp (Aphanius iberus) and a worldwide invasive mosquitofish (Gambusia holbrooki). Critical (Ucᵣᵢₜ) and optimal swimming speeds, standard and maximal metabolic rates, absolute aerobic scope, as well as the minimum cost of transport were estimated and compared between species and sexes. Body streamlining and caudal peduncle depth were also measured to explain the differences in swimming performance and efficiency. Both sexes of A. iberus presented similar swimming capacity and metabolic traits, whereas males of G. holbrooki showed higher critical swimming speeds, maximal metabolic rate and absolute aerobic scope than females. We also found marked differences between species in most of the response variables examined. Aphanius iberus showed lower swimming capacity (Ucᵣᵢₜ mean <10 cm s⁻¹), higher maximal metabolic rate and absolute aerobic scope than the invasive species. By contrast, G holbrooki swam faster and had lower cost of transport at a given fish mass and speed, thereby leading to a higher swimming efficiency. The observed differences in swimming efficiency were closely related to differences in morphological characteristics and therefore to drag pressures and propulsion. Our results add a mechanistic basis to the ecological understanding of these two species and suggest that although both are poor swimmers compared to many other similarly sized species, the native species likely has more restricted water flow tolerance and dispersal capacities.

中文翻译：

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濒临灭绝的本地牙鲤 ( Aphanius iberus ) 和入侵蚊鱼 ( Gambusia holbrooki ) 在游泳性能和能量消耗方面的差异

游泳性能是调节许多鱼类健康和生存的关键特征。使用游泳隧道呼吸计，我们比较了两种竞争物种的长时间游泳性能和能量消耗：濒临灭绝的地方性牙鲤 (Aphanius iberus) 和全球入侵的蚊鱼 (Gambusia holbrooki)。估计并比较了物种和性别之间的临界 (Ucᵣᵢₜ) 和最佳游泳速度、标准和最大代谢率、绝对有氧范围以及最低运输成本。还测量了身体流线型和尾柄深度，以解释游泳表现和效率的差异。A. iberus 的两性表现出相似的游泳能力和代谢特征，而 G. holbrooki 的雄性表现出更高的临界游泳速度，最大代谢率和绝对有氧范围比女性。我们还发现在大多数检查的响应变量中物种之间存在显着差异。与入侵物种相比，Aphanius iberus 的游泳能力较低（Ucᵣᵢₜ mean <10 cm s⁻¹）、最高代谢率和绝对有氧范围。相比之下，G holbrooki 游得更快，在给定的鱼质量和速度下，运输成本更低，从而导致更高的游泳效率。观察到的游泳效率差异与形态特征的差异密切相关，因此与阻力压力和推进力密切相关。我们的结果为这两个物种的生态理解增加了一个机制基础，并表明尽管与许多其他类似大小的物种相比，它们的游泳能力都很差，