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We 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.

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-The objective of this study was to evaluate the performance of three Nile tilapia Oreochromis niloticus strains cultivated in cages and subjected to different feeding programmes. Initially, 31,200 Nile tilapia juveniles with an average weight of 61.15 g were distributed in 48 cages. Two genetically improved strains were used together with one from the Fish Culture Section of Universidade Federal de Lavras (UFLA). The fish were subjected to four feeding programmes, consisting of different levels of crude protein (CP) in diets provided at different stages of cultivation. There was no interaction effect of the strain and feeding programme for most variables. The UFLA strain presented the highest weight gain, but with greatest lack of uniformity at the end of cultivation. The feeding programme with diets containing 36%, 32% and 28% CP, consecutively, promoted the highest weight gain and highest final biomass. The UFLA strain has great growth potential, justifying the development of a breeding programme for this strain. Crude protein levels below 36% for tilapias between 60 and 170 g and below 32% for tilapias between 170 and 700 g worsen fish performance.

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