Screening Of Marine Rhodotorula And Preliminary Study On Its Application In Litopenaeus Vannamei Culture

In recent years,ecological prevention and biological control play an important role in improving aquaculture environment and treating diseases.In this study,93strains of Rhodotorula were isolated from Litopenaeus vannamei culture environment and aquaculture organisms of Litopenaeus vannamei.A total of 28 strains of Rhodotorula were screened through comprehensive analysis of colony and cell morphology,phenotypic characteristics,physiological and biochemical test results.11strains of Rhodotorula mucilaginosa,5 strains of Rhodotorula glutinis,1 strain Rhodotorula acheniorum,2 strains of Rhodotorula araucariae,3 strains of Rhodotorula slooffiae and 4 strains of Rhodotorula chungnamensis were identificated by 5.8S rDNA sequence alignment.strains 711LHt2 and 725BG1s1 may be new species of Rhodotorula sp,Rhodotorula mucilaginosa is the dominant species in this experiment.3 strains with good growth and high carotenoid yield were screened from28 strains of Marine Rhodotorula,which were 506XWb,711LHt1 and 725BG1c2,respectively.The culture conditions were optimized by temperature,pH,inoculum size, salinity and fermentation time by single factor method.The optimal culture conditions were combined into A₁B₁C₂D₂ by orthogonal test,culture time 96h,culture temperature 27°C,NaCl 16g/L,pH:5.0,inoculum size 8%,under the optimized culture conditions,the biological growth of No.2,No.16,No.24 Marine Rhodotorula was 5.35×16⁸ cfu/mL,2.6×10⁸ cfu/mL,4.375×10⁸ cfu/mL.The production of carotenoids was 520.315?g/g,633.32?g/g and 309.65?g/g,which were significantly higher than the growth of caryotenoids and carotenoid production before optimization?P<0.05?.Three strains of Marine Rhodotorula at the ratios of 0%,0.025%,0.05%and0.1%were added to the basic feed of Litopenaeus vannamei respectively to investigate the effects of different dosages of Marine Rhodotorula on the growth, digestive enzyme activity and intestinal flora of Marine Rhodotorula.The experiment showed that the weight gain rate?WGR?,the feed coefficient?FCR?and the specific growth rate?SGR?of the Litopenaeus vannamei were significantly higher than those of the control group when the three Marine Rhodotorula addition amount was 0.025%?P<0.05?.The growth indexes of the experimental group with the addition of Marine Rhodotorula No.2 and No.16 were significantly higher than those of the 24th Rhodotorula?P<0.05?.By studying the digestive enzymes and intestinal microflora of Litopenaeus vannamei the Marine Rhodotorula NO.2 and 16 group,the probiotic mechanism was known.Determination of the digestive enzymes activity of hepatopancreas of Litopenaeus vannamei by adding No.2 and No.16 Marine Rhodotorula,showed a fluctuating state at 10,20 and 40 days,but there was no significant difference among the groups,indicating that the two Marine Rhodotorula had no significant effect on the digestive enzymes activity of Litopenaeus vannamei.The intestinal flora of Litopenaeus vannamei fed with No.2 and No.16 Marine Rhodotorula fluctuated at different concentrations and sampling times.The dominant intestinal flora of Litopenaeus vannamei fed with No.2 Marine Rhodotorula were mainly Bacteroidetes and Proteobacteria.The dominant intestinal flora of Penaeus fed with No.16 Marine Rhodotorula were mainly Bacteroidetes,Firmicutes and Proteobacteria.The intestinal flora of Penaeus fed with Marine Rhodotorula was significantly lower than that of the control group.The results showed that Marine Rhodotorula could increase the growth of Penaeus and decrease the number of intestinal flora,but had no significant effect on digestive enzyme activity.In this experiment,the effects of different amounts of marine red yeast on the astaxanthin content,immune enzyme activity and pathogen stress of shrimp and shrimp shells were studied.The experiment shows that the Astaxanthin content of shrimp shells in the experimental group adding No.2 Marine Rhodotorula was significantly higher than that in the blank control group?P<0.05?.When the addition amount was 0.025%and 0.05%,the Astaxanthin extract content of the shrimp shell was 317.59?g/g and 312.8633?g/g respectively.When the addition of No.16 Marine Rhodotorula group was 0.025%,the Astaxanthin content of shrimp shell was 339.0267?g/g,which was significantly higher than that of the control group and other added groups?P<0.05?.The content of Astaxanthin in other concentration groups was slightly higher than that in the blank control group,but there was no significant difference?P>0.05?.The addition amount and feeding time of Marine Rhodotorula had an effect on the immune enzyme activity of Litopenaeus vannamei.The addition of No.2 Marine Rhodotorula was feeding on the 10th day,and the amount of was 0.025%-0.05%,catalase,lysozyme activity,acid phosphatase activity reached a higher level than the control group and other feeding time.The total superoxide dismutase activity showed fluctuations in each concentration group and different feeding time,no significant difference?P>0.05?.The No.16 Marine Rhodotorula was added to the feeding,and on the 10th day,the whole level of lysozyme activity and acid phosphatase activity of the shrimp was significantly increased;On the 20th day,the amount added was 0.025%in the experimental group,and the catalase activity reached a high level;The total superoxide dismutase activity showed fluctuations in each concentration group and different feeding time,and had no obvious effect. Pathogenic stress test was carried out on shrimp that were continuously fed with Marine Rhodotorula for 40 days.The study found that the mortality of the control group was significantly higher than that of the group of Marine Rhodotorula?P<0.05?,which proved that the experimental strain can effectively improve the disease resistance of shrimp.