The present study was designed to characterize the community structure of parasites of Salminus brasiliensis in the upper Paraná River during different seasons, and to examine the levels of parasitism of this hosts. The community of parasites of S. brasiliensis did not have a dominant species. Four of the five most prevalent parasite species showed aggregate distribution. In relation to other aspects of the community, each group encompassed their particular parasite, which highlights the differences inherent in the biology and life cycle of each species.

Parasitism was observed in 72.7% of 44 specimens of Metynnis lippincottianus (Cope, 1870) (Characidae) caught in the Upper Paraná River floodplain, Brazil. One species of digenean, Dadayus pacupeva Lacerda, Takemoto & Pavanelli, 2003, and four species of nematodes, Spinoxyuris oxydoras Peter, 1994, Contracaecum sp. Railliet & Henry, 1912 (larval stage), Procamallanus (Spirocamallanus) inopinatus Travassos, Artigas & Pereira, 1928 and Raphidascaris (Sprentascaris) mahnerti Petter & Cassone, 1984 were identified. The prevalence of D. pacupeva was correlated with the host's standard length. Correlations between the host's standard length and the abundance of S. oxydoras, P. (S.) inopinatus and D. pacupeva were observed. In addition, fish length was correlated with the diversity of parasites. D. pacupeva and S. oxydoras had their abundances influenced by the host's gonadal m...