Data from: Ectoparasites increase swimming costs in a coral reef fish

Ectoparasites can reduce individual fitness by negatively affecting behavioural, morphological and physiological traits. In fishes, there are potential costs if ectoparasites decrease streamlining, thereby directly compromising swimming performance. Few studies have examined the effects of ectoparasites on fish swimming performance and none distinguish between energetic costs imposed by changes in streamlining and effects on host physiology. The bridled monocle bream (Scolopsis bilineatus) is parasitized by an isopod (Anilocra nemipteri), which attaches above the eye. We show that parasitized fish have higher standard metabolic rates (SMR), poorer aerobic capacities and lower maximum swimming speeds than non-parasitized fish. Adding a model parasite did not affect SMR, but reduced maximum swimming speed and elevated oxygen consumption rates at high speeds to levels observed in naturally-parasitized fish. This demonstrates that ectoparasites create drag effects that are important at high speeds. The higher SMR of naturally-parasitised fish does, however, reveal an effect of parasitism on host physiology. This effect was easily reversed: fish whose parasite was removed 24 h earlier did not differ from unparasitized fish in any performance metrics. In sum, the main cost of this ectoparasite is probably its direct effect on streamlining, reducing swimming performance at high speeds.

体外寄生虫（ectoparasite）可通过对宿主的行为、形态与生理特征施加负面影响，进而降低宿主的个体适合度。对于鱼类而言，若体外寄生虫破坏其躯体流线形态，则可能产生相应适应性代价，直接削弱其游泳性能。目前鲜有研究探讨体外寄生虫对鱼类游泳性能的影响，且尚无研究能够区分由流线形态改变所引发的能量消耗代价，与寄生虫对宿主生理产生的直接作用之间的差异。双线眶棘鲈（Scolopsis bilineatus）会被一种附着于眼部上方的等足类动物（isopod，Anilocra nemipteri）寄生。本研究发现，相较于未被寄生的个体，被寄生的鱼类具有更高的标准代谢率（standard metabolic rate, SMR）、更差的有氧代谢能力以及更低的最大游泳速度。施加模拟寄生虫处理并未对标准代谢率产生影响，但却降低了鱼类的最大游泳速度，并将高速运动下的耗氧率提升至自然寄生个体的观测水平。这表明体外寄生虫会产生阻力效应，该效应在高速运动阶段具有显著影响。但自然寄生个体更高的标准代谢率，确实体现了寄生作用对宿主生理产生的影响。该影响可被轻易逆转：在24小时前移除寄生虫的鱼类，其各项性能指标与未被寄生的个体并无显著差异。综上，该体外寄生虫带来的主要代价，或许源于其对鱼类躯体流线形态的直接破坏，进而削弱了鱼类在高速运动下的游泳性能。