Effects of dietary copper (Cu) on growth performance, body composition, mineral content, hepatic histology and Cu transport of the GIFT strain of Nile tilapia (Oreochromis niloticus)

Abstract

This study determined the influence of dietary copper (Cu) levels on growth and feed utilization, body composition, mineral content, liver histology and intestinal Cu transport, and identify dietary Cu requirement of the GIFT strain of Nile tilapia (Oreochromis niloticus). Six diets were prepared with Cu sulfate addition at levels of 0 (control), 5, 10, 20, 40, and 80 mg/kg, respectively. Analytical dietary Cu contents were 1.55, 2.97, 4.51, 7.25, 11.30, and 19.24 mg Cu/kg diet, respectively. Each experimental diet was fed to three replicates of GIFT tilapia (25 fish per tank, initial body weight 4.34 ± 0.01 g) in a recirculating freshwater system for eight weeks. GIFT tilapia fed 4.51 mg Cu/kg diet had higher growth performance and feed utilization. Cu contents in the whole-body, the liver and intestinal tract increased with dietary Cu levels. Moreover, dietary Cu addition also affected whole-body Mg content significantly, but did not affect whole body crude protein, lipid, zinc (Zn), iron (Fe), and calcium (Ca) content. GIFT tilapia fed with 4.51 mg Cu/kg diet had lower liver vacuoles relative area. Furthermore, dietary Cu addition also significantly influenced mRNA expression of genes involved in intestinal Cu transport, such as copper transporter 1 (ctr1), copper transporter 2 (ctr2), antioxidant 1 copper chaperone (atox1), cytochrome c oxidase copper chaperone (cox17) and copper-transporting ATPase alpha (atp7a). The regression analysis of weight gain and whole-body Cu retention against the dietary Cu levels suggested that 4.23 to 4.57 mg Cu/kg diet was optimal for GIFT tilapia. Statement of relevanceOur study determined the optimal dietary Cu requirement of GIFT strain of tilapia, which provided good references for dietary Cu addition for the fish species, and accordingly was helpful for its feed formulation and aquaculture production. Our study also demonstrated that dietary Cu addition influenced mRNA expression of genes involved in Cu transport, which provides a good basis for exploring Cu metabolism in fish.