Effects Of Isoleucine On Growth Performance And Intestinal Health Of Hybrid Bagrid Catfish

The intestinal health of fish is critical to its growth.The present study was conducted to evaluate the effects of graded Ile(Ile)levels on growth performance and the intestinal health of hybrid bagrid catfish(Pelteobagrus vachelli × Leiocassis longirostris).The 630 fish(33.0±0.1g)were randomly divided into 7 treatment groups(n=30).Fish were feed with 7 different experiment diets for 8 weeks containing graded levels of Ile at 5.0,7.5,10.0,12.5,15.0,17.5 and 20.0 g/kg,respectively.In order to explore the effect of dietary Ile on growth performance and the intestinal health of hybrid bagrid catfish.The main research contents are presented as follows:1.Effects of Ile on growth performance of hybrid bagrid catfishThe results showed that optimal Ile level in diet:(1)the percent weight gain(PWG),feed intake(FI),specific growth rate(SGR),feed efficiency(FE)and protein efficiency rate(PER)were significantly increased(P< 0.05);(2)the crude protein,crude lipid,protein deposition value(PPV),lipid deposition value(LPV)and ash deposition value(APV)were significantly increased(P< 0.05),while the moisture and ash content of fish were no significant difference(P> 0.05);Under the experimental conditions,based on the quadratic regression analysis of PWG,the Ile requirement of hybrid bagrid catfish were12.43 g/kg diet or 32.05 g/kg dietary protein.2.Effects of Ile on intestinal health of hybrid bagrid catfishThe results showed that optimal Ile level in diet:(1)significantly increased the relative gut length(RGL)(P< 0.05),but had no significant effect on the intestinal weight(IW)and intestosomatic index(ISI)(P> 0.05);(2)The intestinal fold height(IFH),intestinal fold width(IFW),intestinal fold sectional area(IFSA),intestinal muscle thickness(IMT)and goblet cells(GCS)of hybrid bagrid catfish were significantly increased(P< 0.05).(3)the mRNA levels of mucin2(MUC2),zonula occludens-2(ZO-2),claudin3 and claudin7 were significantly increased(P< 0.05),while the mRNA levels of ZO-1,occludin,claudin2 and myosin light chain kinase(MLCK)were significantly decreased(P< 0.05);(4)The reactive oxygen species(ROS),malondialdehyde(MDA)and protein carbonyl(PC)contents were significantly decreased(P< 0.05),total superoxide dismutase(T-SOD),catalase(CAT),glutathione-s-transferase(GST),glutathione peroxidase(GPX),glutathione reductase(GR),anti-superoxide anion(ASA),anti-Hydroxyl radical(AHR)activities and glutathione(GSH)content were significantly increased(P< 0.05);(5)The gene expressions of GST,GPx1 a and transcription factor nuclear factor-erythroid 2-related factor2(Nrf2)were significantly increased(P< 0.05);while the Cu Zn SOD,CAT,glutamate-cysteine ligase catalytic subunit(GCLC)and Kelch-like ECH-associated protein 1(Keap1)mRNA levels were significantly decreased(P< 0.05);(6)significantly increased the gene expressions of serine/threonine kinase 1(Akt1),Akt2,Akt3,amino acid terminal kinase 1(JNK1),JNK2,JNK3,and forkhead box protein 6(FOXO6)(P< 0.05),while the mRNA levels of FOXO1,FOXO3 a,and FOXO4 were significantly decreased(P< 0.05);(7)The lysozyme(LZM),acid phosphatase(ACP),alkaline phosphatase(AKP)activities and the contents of complement 3(C3),C4,and immunoglobulin M(Ig M)were significantly increased(P< 0.05);(8)significantly increased the gene expressions of c-type-lectin,c-LZM,g-LZM,and hepcidin(P< 0.05).(9)sirtuin 1(sirt1),ribosome S6 protein kinase(p90rsk),and β-defensin mRNA levels were significantly increased(P< 0.05);while the extracellular signal modulation stimulation 1(ERK1)and ERK2 mRNA levels were significantly decreased(P< 0.05);(10)caspase 3and caspase 9 mRNA levels had no significantly differences(P> 0.05).Collectively,the optimal dietary Ile can improve the growth performance and promote intestinal development;Ile could improve the Nrf2/Keap1,Akt/FOXO3 a and JNK/FOXO4signaling-related molecules gene transcriptions to regulate the antioxidant enzymes related genes expression,and then increase the activities of antioxidant enzymes and antioxidant content,which would reduce the oxidative damage of proteins and lipids and improve the intestinal antioxidant status.Meanwhile,Ile could inhibit the apoptosis of intestinal cell,thus ensuring the integrity of intestinal cells.In addition,isoleucine could promote the expression of MUC2 gene,regulate the expression of tight junction protein gene in fish intestine through MLCK molecule,and improve the tight junction of intestine.Ile could increase the LZM,ACP,AKP activities,C3,C4 and Ig M contents,as well as β-defensin,c-type-lectin,c-LZM,g-LZM and hepcidin gene expressions,and then enhance the chemical barrier function of intestine.Meanwhile,the increase of mRNA levels ofβ-defensin,c-type-lectin and c-LZM was related to the gene transcriptions of sirt1/ERK1/2/p90 rsk signaling molecules.