Estimation of dietary copper requirement of fingerling Indian major carp, Labeo rohita (Hamilton)

The present investigation was conducted to determine the optimal dietary copper requirement of fingerling Labeo rohita (6.5 ± 0.13 cm; 2.46 ± 0.09 g) by feeding seven isonitrogenous (350 g kg⁻¹ crude protein) and isoenergetic (16.7 kJ g⁻¹ gross energy) experimental diets with different concentrations of copper (3.11, 3.63, 4.12, 4.64, 6.13, 9.19 and 15.11 mg kg⁻¹). Each experimental diet was hand-fed to triplicate groups of fish to apparent satiation at 08:00, 12:00 and 16:00 h for 8-week. The group fed with 4.64 mg kg⁻¹ dietary copper exhibited highest (P < .05) live weight gain (LWG), protein efficiency ratio, specific growth rate, protein gain (PG), apparent copper retention and the lowest feed conversion ratio. Increase in dietary copper concentrations exerted significant influence on the body composition, condition factor and somatic indices. Scales, vertebrae and whole body copper concentrations increased (P < .05) with increase in dietary copper levels up to 4.64 mg kg⁻¹ and then stabilized. Liver copper concentration was found to be highest (P < .05) in fish fed 15.11 mg kg⁻¹ copper level and the lowest value (P < .05) was noted in groups fed with 3.11 mg kg⁻¹ copper, while no significant change was recorded in muscle copper concentration. Haematological parameters, serum ceruloplasmin and hepatic total superoxide dismutase, glutathione peroxidase, copper‑zinc superoxide dismutase (Cu-Zn SOD), and catalase activities were highest in groups fed with 4.64 mg kg⁻¹ dietary copper. Significantly lower (P < .05) values of malondialdehyde and lactate dehydrogenase activities were noted in group fed 4.64 mg kg⁻¹ dietary copper. Serum copper concentration and hepatic lipase activity exhibited positive correlation with incremental levels of dietary copper. Broken-line analysis of LWG, PG, whole body and vertebrae copper concentrations, serum ceruloplasmin, and hepatic Cu-Zn SOD activities against different doses of dietary copper were used to determine the copper requirement of L. rohita fingerlings in the range of 4.52–4.75 mg kg⁻¹ diet.