Discussion

When examining the consequences of infection, focus is often placed upon the pathological effects. Some parasites can drastically alter the shape of their host, and in doing so may have an additional physical impact. Ectoparasitic fish lice have been a problem in marine farms for decades, with freshwater lice (Argulus spp.) rising in concern over the past decade. Argulus lice can alter the profile of fish due to their relatively large size and consequently could exert a physical effect on their hosts. Here, using Argulus foliaceus on the model three-spined stickleback (Gasterosteus aculeatus), we examine both physical (including form drag and mass) and pathological effects of infection. Impact was assessed using both sustained (prolonged swimming within an open channel flume) and burst (C-start) swimming performance tests on hosts before, immediately after and days after infection to separate the physical and pathological effects. We then questioned the overall impact of Argulus on fish swimming performance and effect of large parasites on their hosts. Considering the economic cost of parasites, an understanding of the consequences of infection is essential to reduce loss.