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...