Effects Of Dietary Choline On Flesh Quality And Gill Immune Function Of Young Grass Carp (Ctenopharyngodon Idella) And The Mechanisms

Grass carp (average initial weight 266.9±0.6 g) was fed diets containing 197.385,770, 1082,1436 and 1795 mg choline/kg diet, respectively, for eight weeks, which used to research the effects of choline on fish growth performance, flesh quality, gills immune function and determine the choline requirement of young grass carp.The results showed that (1) appropriate choline markedly enhanced growth performance, feed intake and feed efficiency of young grass carp (P< 0.05). (2) Appropriate choline significantly improved flesh quality of grass carp. Muscle protein, fat and some essential amino acids composition as well as muscle shear force, collagen content were elevated by appropriate choline supplementation; oppositely, cooking loss, cathepsin B and L activities were decreased by choline supplementation. Moreover, the decreased muscle cooking loss may be partly due to that choline increased Cu/Zn-SOD, GPx, GST activities and GSH content as well as attenuated muscle oxidative damage. (3) The increased antioxidant enzymes and GSH content in fish muscle may be partly due to the elevated expression levels of these antioxidant enzymes, which maybe regulated by Nrf2, Keap1a and Keap1b.(4) Additional, appropriate choline markedly increased lysozyme, acid phosphatase activities and complement 3 content as well as the relative expression level of hepcidin, LEAP2 mRNA in the gills. Moreover, the relative expression level of IL-10 and TGFβ1 mRNA were up regulated by appropriate choline supplementation,nevertheless, down regulated the relative expression level of IL-1β, TNFα,IFNγ,IL-8, which may be associated with the enhanced expression of TOR,IκBα and decreased expression of NF-κB, IKKβ and IKKy. In addtion. appropriate choline markedly elevated the relative mRNA expression level of occludin,ZO-1,claudin b. claudin c, claudin 3 and claudin 12, which may be partly reguelated by decreased MLCK mRNA level, but there is no difference in claudin 15 mRNA expression.In conclusion, optimal choline improved growth, flesh quality, gill immunity and physical barrier function, and regulated the mRNA levels of related signaling molecules. Based on PWG, the choline requirement for young grass carp (266.5-787.1 g) was 1136.5 mg/kg diet.