Comparing the effect of diet supplementation with different zinc sources and levels on growth performance, immune response and antioxidant activity of tilapia, <i>Oreochromis niloticus</i>

Abstract

The current study was designed as (2 × 3) factorial groups of 20 and 40 mg Zn/kg diet from each inorganic (zinc oxide), organic (Zn-methionine) and nanoparticle (nano-zinc oxide) sources supplemented to six Nile tilapia (O. niloticus) fingerling diets. The results showed both organic and nano-Zn-administered groups, especially at 40 mg/kg, exhibited significant improvements in body weight, total gain, feed conversion ratio and specific growth rate as compared to inorganic Zn-supplemented groups. Nano-Zn, at 20 and 40 mg/kg diet, increased haemoglobin, WBC counts, as well as lysozyme, IgM, and serum bactericidal test compared with other sources. Increasing Zn levels progressively increased serum and muscle Zn contents in nano-Zn groups. Antioxidant capacity (TAC, SOD, and CAT) also increased in nano-Zn-supplemented fish at 40 mg/kg diet. Although the mRNA expression profile of growth hormone (GH) and insulin-like growth factor 1 (IGF-1) showed an up-regulation in both organic and nano-Zn-supplemented fish, a dose-dependent up-regulation was observed for the expression of hepatic antioxidant (SOD and GPx) and immune (IL-1β and TNF-α) encoding genes in nano-Zn-administered groups alone. The highest resistance against Aeromonas hydrophila was observed in the nano-Zn-supplemented group at 40 mg/kg diet. Thus, it can be concluded that zinc nanoparticles are potential alternatives to conventional zinc sources in Nile tilapia.