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. centrostrigeataon 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(Table 2). There was no significant change in the water variables during the study. The observed values were as follows: average temperature: 27.13±0.09°C and 27.71±0.41°C; electrical conductivity: 0.175±1.80 μs cm−1 and 0.181±1.27 μs cm−1 ; DO: 1.64±0.05 mg L−1 and 1.98±0.09 mg L−1 ; and pH: 8.3±0.04 and 8.4±0.04, for tilapia and pacu tanks, respectively