Effects Of Bacillus Natto And Lactosucrose On Growth And Relative Gene Expression Of Juvenile Grass Carp (Ctenopharyngodon Idella)

Grass carp(Ctenopharynodon idellus)is one of the most popular cultured species in China.Grass carp is a favorate species for fish farmers.Meanwhile,it is a delicious,nutritious fish which shows fast growth.Feed additives could stimulate growth of aquatic livestocks,improve feed utilization,prevention of various diseases,reduce the loss of nutrients in feed,and improve quality of aquatic product.Lactosucrose(Ls)can promote growth and improve survival rate.Bacillus natto could produce digestive enzymes,such as proteases,amylases and lipases,induce digestion and absorption of feed.In addition,Bacillus natto could improve morphology of intestinal mucosal,increase villi length and crypt depth deepen.As immunostimulant,Bacillus natto also helpful for treatment of gastrointestinal diseases.The present study used grass carp as subject.The Bacillus natto and lactosucrose were used as feed additives to discuss the effects on growth,metabolism,oxidation resistance,immune system and gene expression.The results are:1.Seperation and identification of Bacillus natto and preparation of high density bacterium dietsUsing fermentation technology to obtain Bacillus natto and prepared diets to feed grass carp,the additive was prepared.The results indicated that among the A,B,C strains from our laboratory,C strain as dry powder had the best activity.After 14 h culture,the Bacillus natto entered the plateau phase and had the best activity.Thus,the following experiment used 14 h cultured Bacillus natto as additive.After 14 h culture,the number of viable cells were 6.78×10~9CFU/ml which was suitable for the present study.2.Effects of Bacillus natto additive on growth of grass carpBy using Bacillus natto additive,the effect of Bacillus natto on growth and serum indexes in grass carp were investigated.By tissues sections,the histology changes after feeding with Bacillus natto additive were analyzed.After added 0.6%,0.8%and 1.0%Bacillus natto in diets,the weight gain and specific growth rate increased significantly.Bacillus natto additive induced protein metabolism and increased serum total protein and urea nitrogen while no changes could be found in fat metabolism.Compared to control,0.4%,0.6%,0.8%and 1.0%additive of Bacillus natto in diets increased T-SOD significantly.Finally,by adding Bacillus natto,the development of foregut and mid-gut were increased.3.Small RNA changes after Bacillus natto additiveThe muscle development-related genes and miRNAs changes after Bacillus natto additive were detected.The results showed that 0.8%and 1.0%additive groups increased expression of miR-1a,miR-181a,miR-23a and miR-206,while myostatin and MEF2C were decreased.Thus,Bacillus natto additive promotes growth of grass carp by regulating expression of muscle development-related genes and miRNAs.4.Effects of lactosucrose additive on growth and liver transcriptome in grass carpInstand of antibiotics,1.5%addition of Ls to feed adolescent grass carp and investigated the transcriptome status of the genes was used.The body weight gain,specific growth rate and feed conversion efficiency were increased to 14.2%,9.2%and 10.1%,respectively after feeding with 1.5%addition of Ls.By biological microarray,we assayed the gene changes in liver after feeding with Ls.In total,416 pairs of genes with different expression were identified.Among them,266 pairs of genes were increased and 150 pairs of genes were decreased.These increased genes were mainly participated into growth,immunization and glucose metabolism while the decreased genes belonged to Ras family and v-myc homologs and apoptosis-related genes.The present results provide basic information for investigation of additives for grass carp and offered preliminary evidences for exploitation of Ls and Bacillus natto.