Regulation Effects Of Antimicrobial Peptide Isalo Scorpion Cytotoxic Peptide(IsCT) On Growth Performance And Intestinal Health In On-growing Grass Carp(Ctenopharyngodon Idella)

In this study,we are the first to investigate the effects of antimicrobial peptide Isalo scorpion Cytotoxic peptide（Is CT）on growth performance,intestinal antioxidant ability and immune function as well as the possible the potential mechanisms of on-growing grass carp.A total of 540 fish（136.88±0.72 g）were randomly divided into six groups for a growth trial and fed six levels of Is CT(0,0.6,1.2,1.8,2.4,and 3.0 mg kg^-1 diet)for 60 days.And then,fish were challenged with A.hydrophila for 6 days to examine the effect of Is CT on intestinal immune function and further related mechanism of on-growing grass carp.The results of our study revealed that,compared with the control group(0 mg kg^-1 diet),appropriate Is CT supplementation in the diet:（1）elevated feed intake（feed intake）,feed efficiency（FE）,percentage weight gain（PWG）,specific weight gain（SGR）and intestinal growth（intestine weight and intestine length）,enhanced the enteritis resistance and the balance of the intestinal microflora of on-growing grass carp;（2）improved intestinal antioxidant ability might be reletaed to enhance the activity of Cu Zn SOD,Mn SOD,CAT,GPx and GST,as well as down-regulated the content of ROS,MDA and PC;（3）icreased the m RNA levels of liver-xpressed antimicrobial peptide（LEAP）-2B,LEAP-2A,hepcidin,mucin2 andβ-defensin-1 and the contents of Immunoglobulin（Ig）M,complement（C）4 and C3 and the activity of lysozyme in the three intestinal segments of fish;（4）attenuated the inflammatory response by up-regulated the studied anti-inflammatory cytokines TGF-β1,TGF-β2,IL-4/13A,IL-4/13B,IL-10 and IL-11m RNA levels,which might be partly regulated to JAK1,JAK2 and JAK3 signalling and STAT3b1/b2（not STAT3a）,STAT5b and STAT6（not STAT2）signalling in the three intestinal segments of fish,and down-regulated the main pro-inflammatory cytokines TNF-α,IFN-γ2,IL-1β,IL-6,IL-8,IL-12p40（except for IL-12p35）,IL-15 and IL-17D m RNA levels in the three intestinal segments of fish,which might be partly regulated to TYK2 signalling and STAT1,STAT4（not STAT2）signalling.In summary,the appropriate Is CT could enhance the growth performance and the balance of the intestinal microflora of on-growing grass carp;And Is CT could increase the enzyme activity of antioxidant enzymes to enhance the intestinal antioxidant ability and increase fish immune substances as well as up-regulate the m RNA levels of endogenous AMP to enhance the intestinal immune function of on-growing grass carp.Further research shows that Is CT could attenuated the inflammatory response by regulate the inflammatory which might be partly regulated to JAKs/STATs Signaling pathway.Finally,based on PWG,SGR,FI,enteritis morbidity,the content of MDA in the PI,ACP and C3 activity in the PI,the optimal dose of Is CT for on-growing grass carp（136.88-507.78 g）were estimated to be1.52,1.53,1.49,2.00,1.75,1.88 and 1.56 mg kg^-1 diet,respectively.