Parasitized animals often display altered behaviours in ways that promote parasite transmission to subsequent hosts in their life cycle. Euhaplorchis californiensis (Euha) is a trematode parasite with a three host life cycle; moving between the California horn snail, the California killifish, and a number of fish-eating bird species. Notably, Euha encycst on the brain of the killifish host and alters its behaviour, which make Euha infected killifish 10-30 times more likely to be eaten by a bird compared to uninfected fish. In order to get a more comprehensive understanding of the behavioural changes underlying this increased transmission rate, we exposed lab-reared killifish to one of four experimental treatments; negative control (seawater), positive control (a low dose of a cyathocotylid trematode), low and high Euha load. Experimentally infected fish and controls were then subjected to a stress regime lasting a total of 90 minutes. Our results show that the behavioural effects of stress are highly affected by infection intensity. Fish infected with a low Euha load spent significantly less time moving compared to the high infected groups. In addition, a low Euha load induced a significantly lower cortisol response to stress compared to the negative control. Conspicuous behaviours associated with increased predation risk were higher in fish exposed to a high load compared to negative controls. We conclude that behavioural patterns associated with increased predation risk are modulated by both presence and intensity of parasite infestation. The next step will be to study brain mechanisms behind this behavioural manipulation.