Effects of dietary manganese source and supplemental levels on growth performance, antioxidant enzymes activities, tissue Mn concentrations and cytosolic manganese superoxide dismutase (cMnSOD) mRNA expression level of juvenile Litopenaeus vannamei

This experiment was conducted to study the effects of different forms and levels of manganese (Mn) on the growth performance, antioxidant activities, tissue Mn content and cytosolic manganese superoxide dismutase (cMnSOD) gene expression of Litopenaeus vannamei. Treatments consisted of 0, 10, 20, 30, 40 and 60 mg Mn kg(-1) from manganese sulphate (Mn-S) and manganese methionine (Mn-Met), providing the actual dietary value of 5.17, 15.62, 25.55, 34.22, 44.48 and 67.90 mg Mn kg(-1) Mn-S, and 5.17, 15.71, 25.36, 35.86, 45.16 and 65.06 mg Mn kg(-1) Mn-Met, respectively. Each diet was fed to triplicate groups of L.vannamei (initial body weight: 1.925 +/- 0.002 g) in a recirculated fresh water rearing system for 8weeks. Weight gain rate (WGR) increased in prawns provided with from 25.55 to 44.48 mg Mn kg(-1) Mn-S and 15.71 to 45.16 mg Mn kg(-1) Mn-Met and then declined above these levels. The lowest protein efficiency ratio (PER) and the highest feed conversion rate (FCR) were observed in prawns fed the control diet (P < 0.05) and showed no significant differences among other treatments (P > 0.05). Survival rate (SR) was not affected by the dietary treatments (P > 0.05). Total SOD and Mn-SOD activities were higher in the hepatopancreas of prawns fed with Mn-supplemented diets from 15.71 to 44.48 mg Mn kg(-1) (P < 0.05). On the contrary, malondialdehyde (MDA) content was lower in the hepatopancreas of prawns fed the basal diet (P < 0.05). Mn concentrations in the hepatopancreas and muscles increased with increasing levels of dietary Mn supplementation. Moreover, Mn accumulation was lower in the muscle than in the hepatopancreas of the prawns. The mRNA expression of cMnSOD gene in the hepatopancreas of prawns was upregulated with increasing dietary Mn levels of Mn-S from 25.55 to 44.48 mg Mn kg(-1), Mn-Met from 15.71 to 45.16 mg Mn kg(-1) and then plateaued above these levels. Broken-line regression analysis of WGR indicated that the optimal dietary Mn requirements for juvenile L.vannamei were 32.26 mg Mn kg(-1) Mn-S and 23.90 mg Mn kg(-1) Mn-Met, respectively.