Investigation of antioxidant defense system, digestive enzymes and histopathological alterations in intestine of catfish, Hetropneustes fossilis exposed to antibiotic norfloxacin

The aim of the present study was to evaluate the toxic effect of an antibiotic Norfloxacin (NOR) on the catfish Heteropneustes fossilis. Four concentrations of NOR such as 0.0025 mg/l, 0.1 mg/l, 4 mg/l and 160 mg/l were selected for the exposure of fish for seven days to study various oxidative stress biomarkers such as lipid peroxidation(LPO), Catalase(CAT), Glutathione peroxidase (GPx) and Glutathione reductase (GR), Superoxide dismutase (SOD), digestive enzymes activity (Amylase, Lipase and trypsin) and the histological (Hematoxylin and Eosin staining) and histochemical (Periodic acid Schiff (PAS) and alcian blue (AB2.5) staining) alterations. Our findings revealed that most of the parameters showed the maximum and minimum changes in 160 mg/l and 0.0025 mg/l NOR treated groups respectively. Furthermore, FTIR spectra also showed a change in the peak positions. In this study, enhanced activity of LPO, SOD, GPx, and GR was noticed whereas, a reduced activity of CAT was noticed in all NOR-treated groups. A digestive enzyme such as amylase was found to increase in the middle and posterior intestine and decrease in the anterior intestine. Furthermore, lipase activity was found to decrease in all three parts (anterior, middle, and posterior) of the intestine. Trypsin activity increased in the anterior and middle intestines and decreased in the posterior intestines in NOR-treated groups. Histological alterations such as disrupted villi, thickened lamina propria, cryptic cell loss, and leucocyte infiltration were observed whereas histochemical changes such as an increased number of neutral goblet cells when stained with PAS and carboxylated acidic mucous cells when stained with AB2.5. This study suggests that the antibiotic NOR causes negative effect on the intestine of fish.