AbstractWe evaluated citric acid supplementation (0, 10, 20, and 30 g/kg) in plant protein‐based diets for juvenile tambaqui, Colossoma macropomum. In Experiment 1, fish (n = 160; 27.56 ± 2.73 g) were distributed in 310 L tanks (n = 16) for 80 days. Zootechnical performance, hematological parameters, and mineral composition (muscle and bones) did not differ significantly (p > .05). The inclusion of citric acid‐reduced pH of diets (p = .001) and stomach (p = .035). In Experiment 2, fish (n = 60; 48.00 ± 1.98 g) were distributed in fecal collection aquaria (200 L) for 21 days. The following were observed: a linear effect for the crude protein (p = .0004) and crude fat (p = .0037) digestibility coefficients; a quadratic effect for crude energy (p = .0037) and dry matter (p = .0004); an optimal supplementation level of 18.5 g/kg. Calcium (p = .0060) and magnesium (p = .0222) showed a linear effect, while phosphorus (p = .0001) had a quadratic effect with the 20 g/kg optimum supplementation level. To conclude, the supplementation of this organic acid in diets does not negatively affect fish nutritional status, health or welfare, and increases nutrient and mineral availability.