In order to minimize bias, each treatment contained 30 fish for biochemical analysis. The whole gut contents of each fish were weighed and homogenized with 9 vol (v/w) of 0.8% physiological saline. Then, the homogenate was centrifuged at 2500×g at 4℃ for 10 min and the supernatant was collected for biochemical assays according to the manufacturer's instructions. Malondialdehyde (MDA) was measured using an enzyme-linked immune sorbent assay (ELISA) kit (Hengyuan, Shanghai). Superoxide dismutase (SOD), peroxidase (POD), reduced glutathione (GSH), acid phosphatase (ACP), and alkaline phosphatase (AKP) were measured using related commercial assay kits (Nanjing Jiancheng Institute,China). Results were recorded on a microplate reader (Epoch, BioTek, USA).
