Thirty five specimens of apaiarí Astronotus ocellatus (Cope, 1872) from Guandu river, (22 degrees 48'32''S, 43 degrees 37'35''W), state of Rio de Janeiro, Brazil were studied for their metazoan parasites from December 2004 to November 2005. A total of six species of metazoan parasites were collected and identified. Gussevia sp. (Monogenea) was the more prevalent species (71.4%) with highest mean intensity value (17.6), followed for the acanthochepalan Polymorphus sp. (cystacanth) which showed prevalence of 17.1%. No parasite species showed significant correlation between the body total length of the host and their prevalence and abundance. The sex of the hosts influenced the abundance of the acanthochepalan Polymorphus sp., being the females more parasitized. The parasite species richness showed a mean value of 1.11+/-0.86 (0-3). The parasite species presented an aggregated distribution pattern.