There were 45 tilapias and 75 pacus used, randomly distributed in 60 liters boxes with continued water flow and fed once a day with 1.5 % of the total body weight. In order to determine the optimum TFB concentration to treat the trichodiniasis in tilapia, we 109 C.V. Ikefuti et al./Experimental Parasitology 154 (2015) 108–112 exposed the fish to 30.0 or 50.0 mg L−1 of the drug for the extent of one hour. Pacu were exposed to 30.0, 50.0 and 80.0 mg L−1 of TFB for one hour or to 50.0 mg L−1 for two hours. All treatments were applied as therapeutic bath, with an interval of 24 hours, during five consecutive days. The stock solution consisted of a known commercial product volume added to water to obtain the desired concentration.
The mortality was monitored daily during the experimental period and the dead fish were removed from the experimental units. The water physical-chemical variables were measured (YSI ® model 556) in the days 1, 3 and 5 after TFB administration. In the sixth day, fish (n=10) that survived were submitted to body surface scrape to isolate the parasites. The presence of trichodinids in the mucus was determined by observation under light microscopy. The anti parasite efficacy was calculated using the following formula: AE=100–[(D×100)/A], where:A is the anti-parasite efficacy (%), A is the trichodinid average before treatment, and D is the trichodinid average after treatment. The survival rate was calculated with the following formula:S=(SF×100)/TF, where: S is the survival rate (%),SF is the number of living fish and TF is the total treatment fish number.