Effects of dietary manganese supplementation on the growth performance, tissue manganese content and antioxidant capacity of coho salmon (Oncorhynchus kisutch) post-smolts

Abstract

A 10-week growth trial was carried out to study the impact of dietary manganese (Mn) level on growth, tissue Mn content and anti-oxidative capacity of coho salmon (Oncorhynchus kisutch) post-smolts (186.51 ± 1.43 g). Six iso-nitrogenous (42.40% Protein) and iso-lipidic (10.27% Lipid) purified diets based on casein-gelatin were formulated to contain varied graded (MnSO4·H2O as a Mn source) levels of 0.40, 9.50, 16.80, 25.80, 33.40 and 41.20 Mn mg/kg. Fish were reared in a freshwater flow-through rearing system and fed to apparent satiation 3 times daily. No significant effects were found on the survival rate, morphological indices, whole-body proximate composition (p > .05) among the groups. However, higher dietary Mn supplementation level than 25.80 mg/kg improved the growth performance, increased the deposition of Mn in whole-body and vertebral, improved hepatic digestive enzyme activity, enhanced anti-oxidative enzyme activities, and decreased the malondialdehyde content in liver and serum (p < .05). Hepatic and serum total antioxidant capacity, glutathione peroxidase, glutathione reductase, total superoxide dismutase, Mn-superoxide dismutase and catalase activities were enhanced with increasing level of dietary Mn, and then stabilized when dietary Mn level up to 25.80 mg/kg. Using the cubic analysis (based on specific growth rate and feed conversion ratio), the optimal dietary Mn levels were 33.25 and 29.55 mg/kg, respectively. Using the broken-line analysis (based on the deposition of Mn, Mn-superoxide dismutase in liver and serum), the dietary Mn requirements of coho salmon post-smolts were estimated to be 24.52, 26.34, 24.74 and 26.05 mg/kg, respectively.