Silymarin enhances the response to oxytetracycline treatment in Oreochromis niloticus experimentally infected with Aeromonas hydrophila.

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 immunosuppression impacts. We, therefore, evaluated the immunological, antioxidative, and histopathological status of Nile tilapia fed a diet containing silymarin (100 mg/kg fish feed) for 0, 2, 4, 6, and 8 weeks. The protective effects of silymarin against Aeromonas hydrophila (A. hydrophila) infection and oxytetracycline treatment were evaluated. Blood parameters (erythrocyte count, white blood cell count, hemoglobin, and packed cell volume) improved over time in fish fed on dietary silymarin. Serum levels of alanine aminotransferase (ALT) were lower in fish fed on dietary silymarin, whereas serum levels of aspartate transferase (AST)and alkaline phosphatase (ALK) were unchanged. Dietary silymarin affected serum lipid profiles as decreases in serum triglyceride and low-density lipoprotein cholesterol levels and a trend toward lower cholesterol levels, whereas serum high-density lipoprotein cholesterol levels were increased compared to fish fed on the control diet. Dietary silymarin resulted in an increase of serum total protein levels and globulin fractions. Significant and progressive increases in catalase and glutathione peroxidase levels were observed after six weeks of feeding on a dietary silymarin before decreasing to control levels at the end of the experimental period. Fish fed on dietary silymarin, interleukin-1 and fish tumor necrosis factor-alpha were upregulated in hepatic tissues; however, interleukin-10 levels decreased to comparable levels to controls after eight weeks. Fish infected with A. hydrophila displayed 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.

Impacts of dietary zinc oxide nanoparticles on the growth and immunity of Nile tilapia could be ameliorated using Nigella sativa oil.

BACKGROUND: Zinc nanoparticles are documented to be harmful to fish because their accumulation in fish bring about many irreversible changes in their health. Nigella sativa and its oil have been endorsed in aquaculture to improve fish health. METHODS: Two hundred seventy experimental fish (113 ± 5 g body weight) were divided into 6 groups G1-6; control fish fed a diet without any treatment (G1), 0.3% of NSO (G2), 0.5% of NSO (G3), ZnO NPs (40 mg/kg diet) (G4), 0.3% of NSO and ZnO NPs (40 mg/kg diet) (G5), 0.5% of NSO and ZnO NPs (40 mg/kg diet) (G6), the trial lasted for six weeks. RESULTS: Growth performance was enhanced in fish received diets containing NSO, final weight (FW), weight gain (WG), daily weight gain (DWG), and relative growth rate (RGR) were significantly increased with lower food conversion ratios (FCR) compared to the control. The hepatic glutathione peroxidase (GPx), catalase (CAT), and metallothionein (MT) were increased in response to ZnO NPs stress and only 0.5% NSO supplementation could ameliorate such increment. The immune-related genes [interleukin1-beta (IL-1ß), tumor necrosis factor-beta (TNF-ß), transforming growth factor-beta 2 (TGF-ß2) and C-type lysozyme] as well as growth-related gene [insulin-like growth factor 1 (IGF1)] in liver showed an upregulation in fish fed with NSO diets. Administration of ZnO NPs lowered the resistance of Oreochromis niloticus against bacterial infection with Aeromonas hydrophila and NSO could enhance the immunity in the highest tested concentration (0.5%) (G6). CONCLUSIONS: The obtained results implied that NSO could enhance the oxidative and immune status of O. niloticus which could compensate ZnO NPs stress as well as experimental infection of a virulent strain of A. hydrophila. Our results revealed that NSO might increase fish growth and immunity only at a high dose (0.5%).

Zinc Oxide Nanoparticles Boost the Immune Responses in Oreochromis niloticus and Improve Disease Resistance to Aeromonas hydrophila Infection.

Zinc is an essential element affecting immune responses in aquatic organisms. In the present research, the immunomodulating effect of zinc oxide nanoparticles (ZnO NPs) was studied in Nile tilapia (Oreochromis niloticus). The minimum inhibitory concentration of zinc oxide nanoparticles (ZnO NPs) for Aeromonas hydrophila was estimated at 60 µg/mL. To evaluate the efficacy of ZnO NPs for improving disease resistance against A. hydrophila, three hundred fish were divided into 5 groups. Fish in the group T1 maintained on the control feed, T2 and T3 feed on ZnO at 60 and 30 µg/g, while T4 and T5 received ZnO NPs at 60 and 30 µg/g, respectively for 8 weeks. Immune responses were evaluated by determining the phagocytic activity, serum antibacterial activity, lysozymes, respiratory burst activity, and also gene expression of immunoglobin M-2, tumor necrosis factor-α, interleukin (IL)-1ß, heat shock proteins, IL-10, insulin growth factor 1, transforming growth factor-ß2, superoxide dismutase enzyme, and catalase enzyme genes. Results indicated that groups that received ZnO NPs have exaggerated immune response and upregulation in the most of expressed immune-related genes. After the feeding trial, all groups were experimentally infected with A. hydrophila, and the mortality rate was monitored. Among all the treated groups, a higher survival rate and disease resistance were observed for fish that received ZnO NPs at 30 and 60 µg/g. The inclusion of ZnO NPs in O. niloticus feed improves both fish immune response and disease resistance against A. hydrophila.