Neophobic behavioural responses of parasitised fish to a potential predator and baited hook

Many juvenile fish show essential avoidance of predators but are also faced with the need to show risky asset-acquiring behaviour, such as trying new food sources, many of which are known to be influenced by parasite infection. Here, we investigated the links between parasite infection, anti-predator behaviour and neophobia towards a novel food presented on a baited hook in fish. Juvenile Spangled perch (Leipotherapon unicolor) undertook two behavioural tests in our laboratory, before being dissected and examined for external and internal parasites. We used an adapted conditioned place avoidance (CPA) paradigm to examine responses to a predator fish and in a separate test, we examined neophobia of a baited hook. Of the 69 Spangled perch studied, 27% of fish were uninfected and at least one of nematodes, Protozoa/Myxozoa or Monogenea were found in the remaining fish. Fish spent less time in the side of the tank where the predator was previously encountered, than before encounters, indicating that fish can learn to avoid locations where predators were previously observed. We found that fish spent longer in the side of the tank where the predator was visible than in the same side of the tank in earlier trials without the predator, supporting previous studies showing that fish actively approach and engage in predator inspection. Fish infected with Protozoa/Myxozoa and camallanid nematodes were less likely to enter the side of the tank with the predator than uninfected fish, suggesting a reluctance to approach a predator in these infected fish. However, Protozoa/Myxozoa and camallanid infected fish bit the baited hook sooner than uninfected fish, possibly indicating less neophobia of the baited hook in fish with these infections. Avoiding to approach a predator yet reduced neophobia to novel foods in some infected fish suggest that parasites do not exert a general, overall, effect on risk aversiveness. Instead, changes in neophobic behaviour appear complex and we discuss the possibility that parasite-induced changes in fish behaviour may be modulated by altered hunger levels and reduced locomotion brought about by illness.