Effects Of Dietary Manganese On Growth, Digestive And Absorptive Abilities, Intestinal Immune Capacity And The Potential Pathway For Young Grass Carp (Ctenopharyngodon Idellus)

To study the effects of manganese on growth performance, digestive and absorptive abilities, as well as the antioxidant and immune capacity and related singling molecules, a total of 540 healthy and uniform-sized fish with an average initial weight of 264±1g (mean±SD) were randomly distributed into 18 experimental cages. Each experimental diet was assigned to three cages in a completely randomized design. The initial weights were not significant in all treatments. The diets contain graded levels of manganese at 3.65 (control),8.62,13.48,18.24,22.97 and 27.86 mg/kg diet for 8 weeks.Study showed that optimum dietary manganese significantly improved the final body weight (FBW), percent weight gain (PWG), specific growth rate (SGR), feed intake (FI), feed efficiency (FE) and protein efficiency ratio (PER)(P< 0.05). The activities of trypsin, lipase in intestine and hepatopancreas, amylase in intestine, alkaline phosphatase, Na+, K+-ATPase, y-glutamyl transpeptidase (y-GT) and creatine kinase (CK) in three intestinal segments were significantly enhanced with optimum manganese supplementation(P< 0.05). The amylase in hepatopancreas was not influenced by dietary manganese levels (P> 0.05). The hepatopancreas weight (HW), hepatopancreas protein content (HPC), intestine weight (IW), intestine length (IL) and intestine protein content (IPC) were significantly enhanced with optimum dietary manganese levels (P< 0.05). However, the intestine length index (ILI), intestosomatic index (ISI) and hepatosomatic index (HSI) were not influenced by dietary manganese levels (P> 0.05). Additionally, dietary optimum manganese significantly decreased the protein carbonyl (PC) and malondialdehyde (MDA) contents in intestine and hepatopancreas (P< 0,05). The intestine and hepatopancreas anti-hydroxyl radical capacities (AHR), manganese superoxide dismutase (MnSOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase activities (GST), as well as the anti-superoxide anion (ASA) in intestine were significantly enhanced with dietary suitable manganese levels (P< 0.05). The ASA was not influenced by dietary manganese levels in hepatopancreas (P> 0.05). Manganese also significantly up-regulated the intestine gene expression of MnSOD, GPx and NF-E2-related factor-2 (Nrf2) (P< 0.05), significantly down-regulated the Kelch-like ECH associating protein 1a (Keap1a) gene expression (P< 0.05). Manganese significantly enhanced the lysozyme and acid phosphatase (ACP) activity in three intestinal segments, as well as the complement C3 in mid intestine and distal intestine (P< 0.05). The complement C3 in proximal intestine (PI) was not influenced by dietary manganese levels(P> 0.05). The further study showed that optimum dietary manganese significantly down-regulated the intestine tumor necrosis factor a (TNF-a), interleukin 8 (IL-8) and nuclear factor-xB (NF-κB) p65 gene expression (P<0.05), up-regulated the intestinal gene expression of interleukin 10 (IL-10), transforming growth factor β1 (TGF-β1), target ofrapamycin (TOR) and inhibitor of κB-α (IκB-α) (P< 0.05). Moreover, the optimum manganese also significantly up-regulated the intestine claudin b, claudin c, claudin 3, claudin 15, occludin and zonula occludens-1 gene expression in intestine (P< 0.05). However, the intestine claudin 12 was not influenced by dietary manganese levels (P> 0.05).In conclusion, optimum dietary manganese promoted the growth, enhanced the digestion and absorption abilities, improved the antioxidant capacity in the intestine and hepatopancreas, as well as the intestinal immune capacity and related singling molecules of young grass carp. Based on the quadratic regression analysis for PWG, MnSOD activity in intestine and hepatopancreas, the manganese requirement for grass carp (264-703 g) were 16.91,18.21 and 18.82 mg/kg diet, respectively.