The study aimed to evaluate phytic acid supplementation at different levels in diets for juveniles of silver catfish. Five diets were prepared with different phytic acid concentrations (0; 5.00; 10.00; 15.00 and 20.00 g/kg). A 50-day biological test was performed in a water recirculation system composed of 20 tanks (15 fish/tank), where the animals were fed three times a day, until apparent satiety with experimental diets. After the experimental period, the fish fasted and were submitted to biometry to collect data, blood and tissues, later used to determine performance, plasma and liver metabolism, activity of digestive enzymes, body composition, digestive indices and activity of pro and antioxidant enzymes. Our results show that the consumption of phytic acid in low concentration (10.00 g/kg) promotes greater performance of fish, better body composition and does not negatively affect the activity of digestive enzymes. In addition, it has reduced the activity of prooxidant enzymes and increased the antioxidants. Thus, we can conclude that when correctly administered and directed, phytic acid acts as an antioxidant and performance promoter for silver catfish.