The present study aims to evaluate the monogenean infestation in Astronotus ocellatus bred in a fish farm in the Peruvian Amazon. Fifty individuals of the species A. ocellatus were collected between July and August 2011 from a semi-intensive fish farm, located in the northeast of the State of Loreto, Peru. This study identified a high infestation in gills by monogenean specie of Gussevia asota in a cultivation of A. ocellatus. The prevalence was 100%, with mortality of all fish. The mean intensity and mean abundance of the parasite were 189.8 of parasites per indi-vidual. This is the first report of infestation high by G. asota in juveniles of A. ocellatus cul-tured from the Peruvian Amazon.