Silymarin enhances the response to oxytetracycline treatment in Nile tilapia experimentally infected with Aeromonas hydrophila

Abstract Many governments have approved the use of oxytetracycline as an antibiotic additive to food fish, with oxytetracycline now routinely used in many nations. However, oxytetracycline is known to have immunological and antioxidant suppression. We therefore evaluated the histopathological, immunosuppressive, and genotoxic effects of a diet containing silymarin (100 mg/kg fish feed) in Nile tilapia at 0, 2, 4, 6, and 8 weeks. The protective effects of silymarin against Aeromonas hydrophila (A. hydrophila) infection were also evaluated. Blood parameters (erythrocyte count, white blood cell count, hemoglobin, and packed cell volume) improved over time in fish fed a silymarin-supplemented diet. Serum levels of alanine aminotransferase, a marker of liver injury, were lower in fish fed diets containing silymarin, whereas serum levels of aspartate transferase and alkaline phosphatase were unchanged. Silymarin supplementation affected serum lipid profiles including decreases in serum triglyceride and low-density lipoprotein cholesterol levels and trend toward lower cholesterol levels, whereas serum high-density lipoprotein cholesterol levels were increased compared to fish fed the control diet. Silymarin supplementation increased serum total protein levels and globulin fractions. Significant and progressive increases in catalase and glutathione peroxidase levels were observed after six weeks of feeding with a silymarin-supplemented diet before returning to control levels at the end of the experimental period. In fish fed a diet containing silymarin, interleukin-1, and fish tumor necrosis factor-alpha were upregulated in liver tissues; however, interleukin-10 levels decreased to comparable levels to controls after eight weeks. Fish infected with A. hydrophila displayed signs of septicemia (opaque eye, hemorrhagic ulcers, dentated fins, hepatomegaly, and splenomegaly). Reduced mortality was observed in Nile tilapia infected with A. hydrophila and fed a diet containing silymarin, indicating that silymarin improves fish responses to oxytetracycline with a 37% reduction in mortality.