DAO prepress abstract  -  doi: 10.3354/dao01918

ABSTRACT: Parasites cause a variety of harmful effects on their hosts, some of which may be overlapping or complementary and thus easily overlooked, but still important for overall severity of infection. We investigated the effect of Diplostomum sp. eye fluke infection on the size of the eye lens in a range of wild and farmed fish species, and those exposed to controlled parasite infection. We found that asymmetry in intensity of infection between right and left lens of an individual fish affected lens size such that the lens with the higher intensity was smaller. Interestingly, however, this was observed only in three of the ten species studied (whitefish, smelt and sea trout) although in these species the effect already became evident at low intensities of infection. Furthermore, the average lens size was significantly smaller in experimentally exposed whitefish Coregonus lavaretus with higher intensity of infection compared to controls, emphasising the sensitivity of this species to parasite-induced changes in lens size. Reduction in lens size may contribute to the deleterious effects of cataract formation by intensifying the effects of individual parasites in the lens. It may also directly affect the overall optical performance of the lens when it is possible that the infection impairs host vision already at low intensities of infection.