Optimization of antibacterial extract from lacquer tree (Rhus verniciflua Stokes) using response surface methodology and its efficacy in controlling edwardsiellosis of olive flounder (Paralichthys olivaceus)

Abstract The purpose of this study was to optimize extraction conditions from Rhus verniciflua (RVS) for antibacterial activity and yield. To obtain an optimized extract (OE) from the lignum of RVS, extracting parameters were optimized by response surface methodology. Optimum extracting conditions were: ethanol concentration, 60%; extracting temperature, 85 °C; and solvent-to-sample ratio (v/w), 30. Under these conditions, regarding the antibacterial activity of OE, its minimum inhibitory concentration was 250 μg/mL. The yield of OE was 10.0%. To investigate the efficacy of OE against Edwardsiella tarda infection in olive flounder Paralichthys olivaceus , fish were fed diets added with OE. Fish administered with OE at 30, 100, or 300 mg/kg b.w./day for 2 and 10 weeks showed significant efficacies, with relative percent survival of 14.3 to 70.0% ( P