The infection, known as yellow spot disease, produced by metacercariae of Clinostomum spp. was studied in fishes of the Taquari river, located in Jataizinho, Paraná State, Brazil. A total of 1,582 specimens, belonging to 36 species, were collected between March 1999 and April 2001. Yellow spot disease was observed only in Gymnotus carapo Linnaeus, 1814 (Gymnotiformes, Gymnotidae) and Cichlasoma paranaense Kullander, 1983 (Perciformes, Cichlidae). This parasitism was generated by metacercariae of Clinostomum complanatum (Rudolphi, 1814) (Digenea, Clinostomidae). Among the 88 specimens of G. carapo examined, 7 (prevalence = 8%) had cysts of the parasite. Four of them were captured in July 1999 and three in October 1999. In the other months, no specimen found was infected. Using relative condition factor (Kn) analysis, it was determined that both infected and non-infected specimens had a total weight equal to the theoretically expected value for each total length (Kn = 1.0). Among 56 individuals of Cichlasoma paranaense, 6 (prevalence = 10.7%) had between 1 and 27 metacercariae of C. complanatum (mean intensity of infection = 9.3 ± 9.6). In March 1999 and April of both 2000 and 2001, the specimens examined were not infected. The infected fish had a total weight higher than the expected value (Kn > 1.0), while the non-infected fish had a weight equal to the expected value (Kn = 1.0).
fish; parasitism; metacercariae; Clinostomum complanatum; Taquari river