Studies On Selection Of Probiotics From The Intestine Of Cynoglossus Semilaevis And Their Application

Cynoglossus semilaevis（C.semilaevis）is a large number of fish cultured in China.In recent years,the number of bacterial diseases of C.semilaevis has increased,which has brought great economic losses to the breeding industry.In this study,a probiotic strain named PP-1 was isolated from the intestine of healthy C.semilaevis.Based on the physiological and biochemical characteristics of the strain and 16 S r DNA gene,the strain PP-1 was identified as Bacillus licheniformis（B.licheniformis）.It was found that the growth characteristics of the strain could be measured at p H 5-9 and salinity10-50 ppt,the temperature of 26-38 ℃;PP-1 drug sensitivity test,the results show that: the bacteria is highly sensitive to ceftriaxone,Cefradine,cefixime,enrofloxacin,moderate sensitive to norfloxacin,penicillin,gentamicin,amoxicillin,piperacillin,and not sensitive to azithromycin,vancomycin.The results showed that B.licheniformis had no pathogenicity to C.semilaevis.After that,the effects on growth performance,serum immunity index and intestinal flora structure of C.semilaevis were studied.The experiment was divided into two groups.The control group was fed with basic diet without B.licheniformis,and the experimental group was fed with diet with B.licheniformis for 21 days.The results showed that compared with the control group,the FBW and WGR of the experimental group increased significantly,the activities of lysozm,ALP and ACP in the serum increased significantly（P < 0.05）,the C3 and C4 in the serum were also increased,which was significantly different from the control group.The results showed that the mortality rate of the experimental group was 30% and that of the control group was80%.The results showed that there were 1168 OTUs in the control group,874 OTUs in the experimental group and 677 OTUs in the two groups.There was a significant difference between the two groups（P < 0.05）.The observed spectrum index,Chao,Ace and Shannon index of the experimental group were lower than those of the control group,while Simpson index was higher than that of the control group.Among the top ten dominant phylum in the experimental group and the control group,Proteobacteria,Actinobacteria,SR1,thermi,BRC1,GN02 and tenericutes were shared by the two groups.In conclusion,the probiotics isolated from the intestine of C.semilaevis is B.licheniformis,which is safe for C.semilaevis.Feeding B.licheniformis can improve the growth performance and immune index activity of C.semilaevis,and improve the resistance of C.semilaevis to Vibrio vulnificus;and can change the intestinal microflora structure of C.semilaevis,which is beneficial to the organism Increase,thus improving the disease resistance of C.semilaevis.