The Effects Of Different Dietary Alpha-linolenic Acid/linoleic Acid Ratios On The Digestive And Absorptive Capacity, Intestinal Immune Function And Its Regulation Mechanism Of Juvenile Grass Carp(Ctenopharyngodon Idellus)

The aim of this study was to investigate the impacts of dietary ALA/LNA ratios on growth performance, digestive and absorptive capacities as well as intestinal immune function of juvenile grass carp (Ctenopharyngodon idellus), thereby evaluate the optimal ratio of dietary ALA/LNA. A total of 1260 healthy and uniform-sized fish (8.78±0.03 g) were randomly distributed into 21 experimental cages. All of the experimental fish were fed diets with different ALA/LNA ratios (0.01,0.34,0.68,1.03,1.41,1.76 and 2.15) for 60 days.The results showed that optimal ALA/LNA ratio significantly improved percent weight gain (PWG) and feed efficiency (FE) of juvenile grass carp (P< 0.05). Meanwhile, data reported herein demonstrated that appropriate dietary ALA/LNA ratio significantly enhanced (P< 0.05):(1) trypsin, chymotrypsin, amylase and lipase activities in the hepatopancreas and intestine, as well as Na+/K+-ATPase, alkaline phosphatase (AKP), y-glutamyl transpeptidase (y-GT) and creatine kinase (CK) activities in the intestine; (2) cholecystokinin (CCK) content in the proximal intestine; (3) mRNA levels of trypsinogen-2, chymotrypsinogen and amylase in the hepatopancreas, as well as Na+/K+-ATPase alpha subunit isoform 1 (atp1a1a.1), Na+/K+-ATPase alpha subunit isoform 8 (atp1a1a.4) and CK gene expression in the intestine; (4) anti-superoxide anion (ASA) and anti-hydroxyl radical capacities (AHR) capacities in the intestine; (5) Cu/Zn superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), glutathion peroxidase (GPx), glutathione-S-transferase activities (GST) and glutathione reductase (GR) activities and gene expression of CuZnSOD, catalase (CAT), GPx, GST and GR, as well as signaling molecules Nrf2 mRNA levels; (6) lysozyme and acid phosphatase activities as well as complement C3 content in three intestinal segments; (7) interleukin 10 (IL-10), transforming growth factor β1 (TGF-β1) and the signaling molecule IκBα gene expression; (8) the tight junction proteins (claudin-3, claudin-b, claudin-c, claudin-12, occludin and ZO-1) gene transcript levels in three intestinal segments of juvenile grass carp. Nevertheless, optimal ratio of dietary ALA/LNA noticeably decreased (P< 0.05):(1) reactive oxygen species (ROS), malonaldehyde (MDA) and protein carbonyl (PC) content as well as CAT activity; (2) interleukin β1 (IL-β1), interleukin 8 (IL-8), tumor necrosis factor a (TNF-a), interferon γ2 (IFN-y2), MnSOD and claudin-15a mRNA levels; (3) relative signaling molecules (Keap1a, Keap1b, NF-κB p65, IKK-p, IKK-y and MLCK) gene expression in the intestine of juvenile grass carp. However, dietary ALA/LNA ratios had no significantly effects on signaling molecule IKKa gene transcriptional abundance in three intestinal segments of juvenile grass carp (P>0.05). In conclusion, optimal dietary ALA/LNA ratio significantly strengthened intestinal immune barrier and physical barrier partly through modulating the relative signaling molecules gene expression, thereby enhancing fish digestive and absorptive capacities, and ultimately improved fish growth performance. Additionally, based on the quadratic regression analysis of PWG, optimal dietary ALA/LNA ratio of juvenile grass carp (8.78-72.00 g) were estimated to be 1.08.