Experimental demonstration of a behavioural modification in a cyprinid fish, Rutilus rutilus (L.), induced by a parasite, Ligula intestinalis (L.)
Behavioural changes in parasitized hosts have been experimentally investigated by comparing the swimming behaviour of roach, Rutilus rutilus, infected by the tapeworm Ligula intestinalis with that of uninfected roach when they were exposed to the same overhead heron stimulus. Before the stimulus was presented, infected fish swam close to the surface and uninfected fish were preferentially found near the bottom of the tank. The stimulus clearly induced a change in the vertical distribution of infected fish only. On the other hand, infected roach were less active than un infected fish before, during, and after the stimulus was presented. Proximate mechanisms of these behavioural changes are discussed. These behavioural differences, i.e., roach surfacing, swimming, and response to stimulus, probably favour the predation of infected roach by avian predators.