Ecological aspects of endohelminths parasitizing Cichla monoculus Spix, 1831 (Perciformes: Cichlidae) in the Paraná River near Porto Rico, State of Paraná, Brazil.

We examined 136 specimens of Cichla monoculus Spix, 1831, collected in the Parana River near Porto Rico, State of Parana, Brazil, from July 1996 through October 1997. Of the total number of fish, 133 (97.8%) were infected with at least 1 species of helminth. A total of 8 helminth species was recorded: 3 Digenea, Clinostomum sp., Diplostomum (Austrodiplostomum) compactum (Lutz, 1928), and Diplostomum sp.; 3 Cestoda, Proteocephalus microscopicus Woodland, 1935, Proteocephalus macrophallus (Diesing, 1850), and Sciadocephalus megalodiscus Diesing, 1850; 1 Nematoda, Contracaecum sp.; and 1 Acanthocephala, Quadrigyrus machadoi Fabio, 1983. Proteocephalus microscopicus and P. macrophallus showed the highest values of prevalence and intensity of infection, followed by Contracaecum sp. In the endoparasite community of C. monoculus, the cestodes are both dominant and codominant species. The typical pattern of overdispersion or aggregation was observed for P. microscopicus, P. macrophallus, S. megalodiscus, Q. machadoi, and Contracaecum sp. Prevalence and total host length were positively correlated in fish parasitized by P. microscopicus, P. macrophallus, and S. megalodiscus. Infection intensity and host length were positively correlated only for P. microscopicus. There were significant differences in the prevalence of P. macrophallus and Q. machadoi in males and females of C. monoculus. Clinostomum sp., Diplostomum sp., D. (A.) compactum, and Q. machadoi were found for the first time in C. monoculus.