Phenotypic modification of roach (Rutilus rutilus L.) infected with Ligulaintestinalis L. (Cestoda : Pseudophyllidea)

In European freshwater, cyprinid fish may be heavily infected by plerocerco ids of the pseudophyllidea cestode Ligula intestinalis (L.). During their d evelopment, these parasites grow rapidly to a large size in the fish's body cavity, characteristically distending the abdomen. In this study, the infl uence of this tapeworm on roach (Rutilus rutilus L.) morphology was analyze d. Forty-five infected and 45 uninfected roach were collected from the Lave rnose-Lacasse gavel pit in Toulouse, South western France and examined for 40 morphological measurements to study phenotypic modification of the body and 14 bilateral characters for an analysis of asymmetry. Results indicate that the degree of bilateral asymmetry does not change between infected and uninfected roach, despite the strong host-morphological modifications such as deformation of the abdomen, fin displacements at the level of the tail, and sagging of the vertebral column. The intensity of abdominal distension and fish morphology changes depends on the total parasite biomass present. Differences were observed in morphology at different levels of infection, which relate to established effects of L. intestinalis on the physiology an d behavior of intermediate hosts. These morphological changes induced by th e parasite could increase trophic transmission to the definitive avian host s.