The effects of quercetin on immunity, antioxidant indices, and disease resistance in zebrafish (Danio rerio)

The main purpose of this study was to evaluate the immunity, antioxidant indices, and disease resistance of quercetin in zebrafish (Danio rerio). A total of 630 fish were assigned to 21 tanks with 30 fish/tank, and they were exposed to 0, 0.01, 0.1, 1, 10, 100, and 1000 μg/L quercetin, respectively, for 56 days. Results indicated that the immune indices including acid phosphatase (ACP), myeloperoxidase (MPO), lysozyme activities, and Complement 3 (C3), C4, IgM contents were significantly higher in 1 μg/L quercetin group than these parameters in the control group (P < 0.05). TNF-α and IL-8 mRNA expressions significantly decreased as the levels of quercetin increased up to 1 μg/L and increased thereafter (P < 0.05). 1 and 10 μg/L quercetin groups showed significantly lower TNF-α and IL-8 mRNA levels than the quercetin-free group. Transforming growth factor-β and IL-10 mRNA levels showed an obviously opposite trend with TNF-α expression. The SOD, GPX, CAT, T-AOC activities, and SOD and GPX gene expression in the liver were enhanced with increasing quercetin up to 1 μg/L, and decreased thereafter. MDA contents were affected by quercetin, in which 1 and 10 μg/L quercetin had a significantly lower level than that of the control group (P < 0.05). Defensin and Leap-II mRNA expression in the liver were the highest for fish exposed to 1 μg/L quercetin. The fish that exposed to 1 μg/L quercetin also showed a significantly higher survival rate than these of fish exposed to 0, 0.01, and 1000 μg/L quercetin (P < 0.05). In conclusion, the optimal level of quercetin promotes immunostimulant properties, antioxidant indices, and disease resistance of zebrafish.