Cost of exposure to trematode cercariae and learned recognition and avoidance of parasitism risk by fathead minnowsPimephales promelas

Fathead minnowsPimephales promelasexposed to cercariae of the trematodeOrnithodiplostomumsp. incurred a significant mass loss 17 days after exposure to 20 or 120 cercariae. Parasite‐naïveP. promelasshowed no evidence of innate recognition or avoidance of cercariae. After a single exposure to cercariae, however, fish responded to chemical and visual cues of dead (thawed) cercariae with a reduction in activity. Encounter rate with cercariae, and hence infection rate, increased with fish activity. The data indicated that experiencedP. promelasassociated parasitism risk with novel chemical and visual cues that later triggered avoidance behaviour. Parallels and interactions between antiparasite behaviour and antipredator behaviour open new avenues for behavioural ecological research in risk‐sensitive decision‐making.