Larvae of the eye-fluke, Diplostomum, emerge from snails and infect fish by penetrating skin or gills. Inside, it moves to the lens where it may impair the vision of the fish. For the fluke to reproduce, a bird must eat the infected fish, and it has been suggested that they actively manipulate the fish's behaviour to increase the risk of predation. I found parasite prevalence’s of 90-100 % in invasive round gobies (Neogobius melanostomus) from the Kalmar Sound, Baltic Sea. I investigated if the intensity of parasite-induced cataract was related to behavioural alterations in round gobies. My results suggest that round gobies with intense cataracts had a reduced response to simulated avian attack. However, other anti-predator behaviours, i.e. light intensity preference, shelter use and boldness were not impaired. My results are in accordance to the idea that parasites change host behaviour to their own advantage, and may have implications for the success of invasive round goby populations.