Do gill parasites influence the foraging and antipredator behaviour of rainbow darters, Etheostoma caeruleum?

Parasites are known to affect an array of characteristics of their hosts, including morphology, physiology and behaviour. We examined the foraging and antipredator behaviour of rainbow darters, Etheostoma caeruleum, that were parasitized by glochidia larvae of freshwater mussels (Ptychobranchus occidentalis and Venustaconcha pleasii: Unionidae). Glochidia attach to the gills of the host and become encapsulated in host tissue. Over a period of days or weeks the larvae develop into free-living juveniles, which then leave the host. Parasitized darters increased ventilation rates (either early in the infestation or at the height of the infestation), were less active during foraging trials, lost more body size than nonparasitized darters and showed significantly weaker responses to predation risk (signalled by the presence of a chemical alarm cue). Therefore, even for a relatively short-term infection, parasitized darters may pay a cost in terms of decreased growth and decreased probability of survival.

► Darters increased ventilation early and at the height of glochidial infestation. ► Parasitized darters decreased activity during foraging trials. ► Darters that were parasitized lost relatively more body size. ► Parasitism weakened responses to predation risk.