The average weight for pacu was 71.01±4.34 g and for tilapia was 103.37±17.53 g. Groups of fish (120 each) belonging to the same species were maintained in tanks containing 400 liters of water with low dissolved oxygen concentration (DO) (below 4.0 mg L−1), overload of organic matter, fed each 48 hours and periodic capture simulations. Periodic samples from both species (n=10) were submitted to body surface scraping and gills removal to quantify the presence of parasites (Madsen et al., 2000). The parasite quantifications were performed with complete integument scraping and the removed gills were put on a glass slide when still fresh, and determined by direct counting and light microscope observation (1000×zoom).