Dietary Copper Requirement of Cirrhinus mirigala Juveniles: Effects on Growth Performance, Antioxidant Enzyme...

The present study aimed to determine the optimum dietary Cu requirements and the growth and health of Cirrhinus mrigala juveniles. For this purpose, six isolipidic and isonitrogenous diets were prepared, including a control diet and five experimental diets supplemented with varying levels of dietary Cu in a graded manner (2, 4, 6, 8, and 10 mg/kg from CuSO₄.5H₂O). The analyzed contents of Cu were determined to be 1.24, 2.21, 4.22, 6.21, 8.20 and 10.19 mg/kg in the diets. Each diet was hand-fed to triplicate groups of 15 fish (initial weight 7.73 ± 0.06 g) to apparent satiation for 60 days two times a day. The results revealed a significant (p < 0.05) increase in growth with increasing dietary Cu concentrations up to 6.21 mg/kg, after which growth decreased. The feed intake (FI) significantly (p < 0.05) increased and feed conversion ratio (FCR) decreased with increasing Cu concentration to 6.21 mg/kg. Body indices and whole-body proximate composition significantly (p < 0.05) improved as the dietary Cu concentration increased to 6.21 mg/kg. Copper absorption and Cu content in muscles, bones, scales, kidneys and the whole body linearly increased with increasing dietary Cu levels and peaked at 6.21 mg/kg and then leveled off. Antioxidant enzyme activities significantly increased with increasing Cu supplementation, peaking at 6.21 mg/kg and then stabilizing; however, opposite trend was observed in thiobarbituric acid reactive substances (TBARS). Alkaline phosphatase (ALP) activity linearly increased with increasing Cu levels up to 6.21 mg/kg and then plateaued. The optimum Cu requirements of Cirrhinus mrigala juveniles were 5.60-6.21 mg/kg.