Citric acid minimizes oxidative stress in Amazonian fish (Colossoma macropomum) when fed plant protein-based diets

This study aimed to evaluate the antioxidant potential of citric acid in plant protein based-diets offered to juvenile tambaqui, Colossoma macropomum. Four isonitrogenous and isoenergetic diets containing different levels of citric acid (0, 10, 20, and 30 g.kg−1) were formulated. Fish (n = 160; 27.56±1.03 g) were randomly distributed in 310-L water tanks (n = 16), with four replicates per treatment. After the experimental period (80 days), animals were anesthetized, and blood was collected for cell count. They were euthanized and dissected to remove livers for subsequent oxidative stress analyses. No significant differences were observed in the levels of thrombocytes, total leukocytes, lymphocytes, positive granular leukocytes, and immature leukocytes among the experimental treatments. However, there were fewer monocytes and neutrophils in fish fed the diet containing 30 g.kg−1 of citric acid. All citric acid diets increased glutathione concentration and reduced lipid peroxidation levels in livers. Therefore, citric acid acts as a potent antioxidant in juvenile tambaqui fed plant protein-based diets and, thus, can improve their maintenance conditions in production system