Dietary magnesium requirements of juvenile grass carp, Ctenopharyngodon idella

To determine dietary magnesium (Mg) requirements of juvenile grass carp, Ctenopharyngodon idella, magnesium sulphate was added to the basal diet at 0, 150, 300, 600, 1200, 2400 mg Mg kg⁻¹ diet. Each diet was fed to three replicate groups of juvenile grass carp (initial weight: 7.69 ± 0.13 g) in a closed, recirculating rearing system for 76 days. No mortality or nutritional deficiency signs were observed except the growth depression in fish fed the Mg-deficient diet. Growth performance and activities of serum superoxide dismutase (SOD), glutathione peroxidase (GPx) and lysozyme (LSZ) were highest (P