Quercetin-mediated concentration-related regulation of intestinal enzyme activities and microbiota in Siniperca chuatsi
Description
Quercetin is a plant flavonol with antioxidant, antibacterial and immunomodulatory activities, and its effects on the fish intestine have been examined mainly through dietary supplementation. This study measured intestinal enzyme activities and microbiota composition in mandarin fish (Siniperca chuatsi) after 28-day immersion exposure to quercetin at 0, 1, 2.5 and 5 mg/L. Pyruvate kinase activity was lower in all quercetin-treated groups than in the control. Amylase activity was higher at 1 mg/L only. Pepsin activity was suppressed at 2.5 and 5 mg/L. Lipase did not show consistent concentration-dependent changes. The three enzyme responses dissociated across concentrations: pyruvate kinase responded irrespective of dose, amylase responded only at the lowest concentration, and pepsin responded only at the two higher concentrations. Intestinal microbiota composition differed among groups, with the 5 mg/L group separating from the control in PCoA and showing the lowest Simpson index. Edwardsiella was higher at 1 mg/L and lower at 5 mg/L. Acinetobacter, Edwardsiella and Cetobacterium were the dominant genera across groups. These findings establish a concentration-resolved basis for evaluating waterborne quercetin in mandarin fish and identify amylase, pyruvate kinase and Edwardsiella as responses that differ in their concentration dependence, providing a framework for designing dietary trials that test whether these intestinal effects translate into nutritional or health benefits.