An experimental research was carried out with the purpose of evaluating the phytobiotic effect of oregano (Origanum vulgare) and garlic (Allium sp.) On the increase in weight and the feed conversion of juveniles of Colossoma macropomum, according to a completely randomized design with four treatments: control (TC:Rb), base ration with oregano (TA:Rb+O), base ration with garlic (TB:Rb+A) and the combination of both with the base ration (TAB:Rb+O+A). The research included a study population of 120 fish, distributed in twelve experimental units of 10 specimens each, with average total weights and sizes of 1.43 g and 3.7 cm, respectively. Weight gain (GP), weight increase (IP), specific growth rate (TCE), apparent feed conversion (CAA) and feed efficiency (EA), were the biological parameters that allowed to evaluate the effect of the experimental rations. According to the results, it was det...