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 . 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).