Abstract
The present investigation was performed to evaluate the efficiency of Zinc oxide (ZnO) as a fish feed additive in immunomodulation of Oreochromis niloticus. Fish were fed on ZnO nano-particles (nZnO) and conventional (ZnO) in two concentrations (30 and 60 mg/kg diet), in addition to the control fish which was fed on Zn free diet. After 6° days, the highest survival rate was recorded in the nZnO30 –supplemented group. The total antioxidant capacity (TAC) and antioxidant enzymes were improved in different dietary Zn supplementation, obviously in the nZnO30 –supplemented group, while the lowest antioxidant status was noticed nZnO60 supplemented fish. The lipid peroxides (MDA) level was diminished upon Zn supplementation, particularly in nZnO30-supplemented group but showed a significant elevation in the nZnO60-supplemented group. Furthermore, the immune parameters examined, lysozyme activity, bactericidal activity, and IgM were significantly higher in ZnO60, and nZnO30 supplemented groups. The C-reactive protein (CRP) level showed no significant increase in response to Zn supplementation in the both forms at level of 30 mg/kg diet, but showed marked elevation in nZnO60- supplemented group. The mRNA expression profile of both interleukin 8 (IL-8), interleukin 1, beta (IL-1β) encoding genes showed an up-regulation that was found in all Zn- supplemented groups, but more pronounced in nZnO60-supplemented group. On the other hand, the expression pattern of myxovirus resistance (Mx)-encoding gene showed no remarkable difference between the Zn- supplemented and control fish. The expression level of CXC-chemokine, toll-like receptor 7 (TLR-7), immunoglobulin M heavy chain (IgM heavy chain) and interferon gamma (IFN-γ) gene was upregulated in Zn-supplemented groups particularly in the nZnO30- supplemented group. While, the lowest expression was found in nZnO60- and ZnO30-supplemented groups. Here, Zn supplementation promoted the immune and antioxidant strength in fish mainly in nano form at the level of 30 mg/kg diet but not at 60 mg/kg diet that disrupt the immune and antioxidant status and promote inflammatory response.
•In fish, nano-Zinc promotes the immune and antioxidant strength at the level of 30 mg/kg diet.•Nano-Zinc at 60 mg/kg diet mediates oxidative and inflammatory injuries.•Conventional Zinc at the level of 60 mg/kg improves the immune and antioxidant status of fish.•Zinc had a more pronounced immune modulating effect at the genomic level.•Zinc nano-form at low concentration is a promising feed additive in fish farms and aquaculture.