Biofloc Technology System (BFT) is a rearing method that uses microorganism communities to preserve water quality and improves several biological parameters of Pacific white shrimp Litopenaeus vannamei. The water of a BFT system received four different concentrations of the antioxidant quercetin every 24 hr plus a control treatment, without adding quercetin. During 7 days, several water quality parameters were analysed daily. Results indicated that all parameters remained in the optimal range for L. vannamei. In a second experiment, shrimps were maintained in a BFT system with (1 mg/L) or without quercetin addition during 30 days. At the end of the experimental period, it was measured total flavonoids content and lipid peroxidation in muscle and hepatopancreas of shrimps. The results indicated that: (a) flavonoid content in muscle and hepatopancreas of shrimps increased after 10 and 20 days of quercetin treatment, respectively; (b) lipid peroxidation was reduced in both organs after antioxidant treatment; (c) weight gain was improved in quercetinsupplemented shrimps. It is concluded that bioflocs of BFT systems treated with quercetin increased their antioxidant capacity without changing water quality parameters for the appropriate development of shrimp culture and improved growth and reduced the oxidative damage of reared organisms. K E Y W O R D S antioxidant supplements, BFT, flavonoids, functional food, water quality