In the initial quantification, pacu presented an average of 173.9±80.4 Trichodina fish, while tilapia numbers were higher than 300Trichodina fish . No trichodinids were found on the gills. The four Trichodina species were T. magna, T. compacta and T. centrostrigeata on tilapia and T. heterodentata on pacu. In tilapia, the reduction was 87.9%, from an average of 140.0±1.4 parasite fish in control to 17.0±24.5 parasite fish in fish exposed to 50.0 mg TFB L −1 for one hour. In pacu, we observed a reduction of 96.1%, with an average of 176.3±80.9 parasite fish in control and 6.5±10.64 parasite fish after treatment with 80.0 mg L−1 for one hour (Table 1). Tilapia survival during the efficacy experiments ranged from 60.0% to 90.0% in the groups treated with TFB, whereas the fish from non-treated groups had a survival rate of only 13%. For pacu, the survival rate ranged from 86.0% to 100.0%, and no mortality was observed in the non-treated group