Growth performance, tissue mineralization, antioxidant activity and immune response of oreochromis niloticus fed with conventional and gluconic acid zinc dietary supplements

Zn is one of the essential elements to maintain normal fish metabolic process (including growth, development and reproduction), which have different chemical status in nature including inorganic, organic and nano-sized. In this work, the efficacy of gluconic acid zinc (Glu-Zn), nano zinc oxide (Nano ZnO), zinc sulphate (ZnSO₄) on the growth performance, tissue mineral elements deposition, antioxidant activity and immune response of the tilapia fish Nile tilapia (Oreochromis niloticus) was evaluated. Three experimental diets were prepared by adding different forms of Zn sources (ZnSO₄ as a control group) with same Zn concentration (40 mg/kg) and used to feed fish for 60 days. The biological trial results displayed that the growth performance of Nile tilapia has not obviously affected by different Zn form source supplement. However, Glu-Zn and Nano ZnO supplements have significantly stimulated the Zn and Cu absorption deposition efficiency in the fish tissues as compared to ZnSO₄ group. Besides, there was a significant increase in Cu-Zn superoxide dismutase (35.03 U/mgprot), alkaline phosphatase (79.34 U/mgprot), aspartate aminotransferase (23.42 U/L), alanine aminotransferase (18.45 U/L), glutathione peroxidase (171.24 U/mgprot) and fatty acid synthase (11.55 ng/mL) content in Glu-Zn treatment. Additionally, Glu-Zn supply significantly increased serum lysozyme (9.91 U/mL), immunoglobulin M (0.48 g/L), complement 3 (0.74 g/L) and complement 4 (0.95 g/L) activity of Nile tilapia. Also, compared to ZnSO₄ diet, lysozyme (11.44 U/mL) and complement 4 (0.63 g/L) content were obviously higher in fish fed Nano Zn diet. These findings revealed that supplementation with Glu-Zn as a Zn source in feed is better than ZnSO₄ for improving tissue mineralization, antioxidant stress, alleviate lipid peroxidation and immunity response of Nile tilapia. Meantime, Nano ZnO also played a positive role in the tissue mineralization and immunity response of Nile tilapia.