Pathogenicity of Clinostomum complanatum (Digenea: Clinostomidae) in naturally infected chub (Squalius cephalus) and common carp (Cyprinus carpio)

Metacercariae of the digenetic trematode Clinostomum complanatum Rudolphi, 1814 were observed in chub (Squalius cephalus) and common carp (Cyprinus carpio) from the Orljava River (Croatia). Both the prevalence and infection intensity were higher in the chub (prevalence 23.4%, average intensity 70.5) than in the common carp (5.9%, 4.5). In general, the metacercariae were located in the wall of the anterior part of the digestive tract and branchial cavity, the supraocular region, and the hypaxial musculature near the paired fins. Histology revealed the obvious affinity of the parasite for striated muscles and connective tissue. In situ, the metacercariae were surrounded by wellvascularized connective tissue capsules composed primarily of collagen fibers, fibroblasts, and fibrocytes. This study provides some insight into the parasite’s pathogenicity and the relationship between host and parasite.