Effects Of Adding Bacillus Megaterium To Plant Protein Meal On Growth Performance And Immunity Of Juvenile Hybrid Sturgeon And Its Mechanism

This experiment was conducted to study the effects of adding Bacillus megaterium to plant protein meal on growth performance and immunity of juvenile hybrid sturgeon(Acipenser schrenckii?�Acipenser baeri?).The fish in the 4 experimental groups were fed plant protein meal(group PM)with 106 cfu/g Bacillus subtili(group ?),105 cfu/g(group ?),106 cfu/g(group ?)and 107 cfu/g Bacillus megaterium(group ?),respectively,taking the fish meal(group FM)and group PM as control groups.After the acclimation,A total of 750 juvenile hybrid sturgeon with an initial body weight of(12.87�0.65)g were randomly divided into 6 groups with 5 replicates and 25 fish per replicate.During the experiment,the water temperature controlled in 21�0.5?,and dissolved oxygen is greater than 5 mg/L,and keep in the natural light.The fish was fed 3 times a day by hand to apparent satiation at 7:00,12:00,and 17:00.At the same time,recording the amount of feeding,regularly change water,disinfection,to ensure good water quality.The experiment was lasted for 8 weeks.The results showed as follows:(1)The final weight and weight gain rate were higher in group FM compared with the other groups(P<0.05),and the group ? was higher compared with group PM(P<0.05).The feed efficiency ratio were lower in group FM and group ? compared with the other groups(P<0.05),and the group ? was lower compared with group PM(P<0.05).The protein efficiency ratio were higher in group FM and group ? compared with the other groups(P<0.05),and the group ? was higher compared with group PM(P<0.05).The dietary Bacillus megaterium levels had no significant effect on the viscerosomatic index,dry matter,crude lipid,crude protein and ash of whole body(P>0.05).(2)The content of lysozyme(LSZ),the activity of alkaline phosphatase(AKP)were higher in serum and liver in group FM,group ? and group ? compared with the group PM(P<0.05).The activity of MPO were higher in serum in group ? and group ? compared with the group PM(P<0.05).The activity of myeloperoxidase(MPO)were higher in liver in group ? compared with the group PM and group ?(P<0.05).The mortality rate of juvenile hybrid sturgeon after challenged with Aeromonas hydrophila in group FM and all experimental groups were lower compared with the group PM.(3)The total protein(TP)content and the globulin(GLB)content were higher in serum in group FM and all experimental groups compared with the group PM(P<0.05).The content of uric acid(UA)were lower in serum in group FM and group ? compared with the group PM(P<0.05).The activity of alanine transarninase(ALT)were lower in serum in group FM and group ? compared with the group PM(P<0.05).The activity of aspartate aminotransferase(AST)were lower in serum in group?,group ? and group ? compared with the group PM(P<0.05).The content of glucose(Glu)were lower in serum in group ? compared with the group PM(P<0.05).(4)The content of glutataione(GSH),the activity of total antioxidant activity(T-AOC),antisuperoxide anion free radical(ASAFR)and superoxide dismutase(SOD)were higher in serum,liver and duodenum in group ? compared with the group PM(P<0.05).The activity of catalase(CAT)were higher in serum in group ? compared with the group PM(P<0.05).The activity of xanthine oxidase(XOD)were lower in serum and liver in group ? and group ? compared with the group PM(P<0.05).The content of GSH,the activity of T-AOC and SOD were higher in pyloric caeca in group ?,group ? and group ? compared with the group PM(P<0.05),and had no significant difference with the group FM(P>0.05).(5)The protease activity in stomach,intestine were higher in group ? and group?compared with the group PM(P<0.05).The amylase activity were higher in stomach,pyloric caeca and intestine in group FM and group ? compared with the group PM(P<0.05).The amylase activity in stomach were higher in group ? compared with the other groups(P<0.05).The lipase activity were higher in stomach,pyloric caeca and intestine in group FM and group ? compared with the group PM(P<0.05).(6)The NF-kB,HSP90 and HSP70 relative gene expression in group ? and group? were higher in spleen compared with the group PM and group FM(P<0.05).The NF-kB,HSP70,MyD88 and HSP90 relative gene expression in intestine were higher in group?compared with the group PM(P<0.05).(7)The villus height and muscular thickness were higher in duodenum in group FM,group ?,group ? and group ? compared with the group PM(P<0.05).The folds depth were higher in duodenum in group ? and group ? compared with the group PM(P<0.05).The villus height,folds depth and muscular thickness were higher in valvula intestine in group FM,group ? and group ? compared with the group PM(P<0.05).(8)The value of Ace were higher in group ? and group ? compared with the other groups.The value of Chao and Shannon were higher in group ? compared with the other groups.The value of simpson were higher in group ?,group ? and group ?compared with the group PM.In category level,fusobacteria and firmicutes are the main bacteria in intestinal contents of juvenile hybrid sturgeon.With the increase of Bacillus megaterium added,relative abundance of firmicutes gradually increased,relative abundance of fusobacteria and proteobacteria decreased.It is concluded that plant protein meal supplemented appropriate Bacillus megaterium levels has a positive effect on the weight gain rate and the protein utilization rate and enhance the activities of intestinal digestive enzyme,promote the development of intestinal morphology,regulate the intestinal flora.What's more,plant protein meal supplemented appropriate Bacillus megaterium levels can enhance the antioxidant capacity,nonspecific immune and up-regulate the relative expression of immunity genes.In conclusion,the effects of adding 105 cfu/g Bacillus megaterium to plant protein meal on growth performance and immunity of juvenile hybrid sturgeon is better.