Manganese (Mn) is an essential trace element in shrimps serving as a cofactor for exoskeleton development, metabolic processes and immune responses. Limited information is available on Mn requirement for Pacific white shrimp under low-salinity condition. This study, therefore, was conducted to evaluate the requirement of dietary Mn and its effects on growth performance, innate immunity, antioxidant capacity and disease resistance of the shrimp reared under low-salinity condition.
A basal diet (Mn0) containing 10% fish meal (anchovy), 25% corn gluten meal and 3% fish oil (cod liver) was formulated. The experimental diets were prepared to contain 20, 40, 60, 80 and 100 mg/kg Mn (designated as Mn20, Mn40, Mn60, Mn80 and Mn100, respectively). Total 450 shrimp (initial BW: 0.62 ± 0.01 g) were randomly distributed in 18 tanks (240 L) with 25 shrimp per tank. Triplicate groups of shrimp were fed one of the diets six times daily for 56 days. Salinity of the rearing water was maintained at 10 ppt. After the feeding trial, a bacterial challenge test against Vibrio harveyi was conducted.
Growth performance (final body weight, weight gain and specific growth rate) was significantly higher in Mn60 group than in Mn0 group. Feed utilization efficiency (feed conversion ratio and protein efficiency ratio) and survival were not significantly different among all the groups. Superoxide dismutase activity was significantly enhanced in Mn40, Mn60 and Mn80 groups than in Mn0 group. Glutathione peroxidase activity was significantly improved in Mn60 group than in Mn0, Mn20 and Mn100 groups. Catalase activity was significantly higher in Mn60 group than in Mn0 and Mn100 groups. Disease resistance against V. harveyi was significantly improved in Mn60 group than in Mn0 group.
The optimal dietary Mn supplementation can improve the growth performance, antioxidant capacity and disease resistance against V. harveyi of Pacific white shrimp under low-salinity conditions. Based on quadratic regression analysis of weight gain, the Mn requirement was estimated to be 66.1 mg/kg for Pacific white shrimp under low salinity condition.