Dietary manganese requirements of juvenile tilapia, Oreochromis niloticus × O. aureus

To quantify the dietary manganese (Mn) requirements of juvenile tilapia (Oreochromis niloticus × O. aureus), manganese sulfate was added to the basal diet at 0, 3, 6, 10, 15, 20, 30 and 60 mg Mn/kg diet providing the actual dietary value of 2.89, 5.86, 8.57, 13.54, 18.51, 23.48, 33.37 and 63.43 mg Mn/kg diet, respectively. Each diet was fed to triplicate groups of tilapia (initial body weight 0.64 ± 0.02 g) in a recirculated fresh water rearing system for 8 weeks. The Mn concentration in rearing water was monitored during the feeding period and was 1.0 μg Mn/l. Weight gain, feed efficiency and survival of tilapia were not affected (P > 0.05) by the dietary treatment. Hepatic, bone and muscle Mn concentrations were increased as the dietary Mn supplementation level increased. Hepatic Mn superoxide dismutase (Mn SOD) activity was higher (P < 0.05) in fish fed diets with 5.86–33.37 mg Mn/kg diet than that in fish fed the Mn-unsupplemented control diet. Analysis by broken-line regression of hepatic Mn SOD activity and by linear regression of whole body Mn retention indicated that the adequate requirement of dietary Mn for juvenile tilapia is 7 mg Mn/kg diet.