Study On The Effects Of Lactococcus Lactis And Astaxanthin On The Growth,Intestinal Flora And Antibacterial Ability Of Litopenaeus Vannamei

Lactic acid bacteria(LAB),as a recognized important probiotic,is widely used in aquaculture.Current evaluations of effects are mostly focused on Lactobacillus plantarum.The effect of Lactococcus lactis is still unclear;astaxanthin is another A commonly used feed additive for aquatic products also has an equally important position,but its effect in Litopenaeus vannamei is rarely reported.To this end,this article intends to study the effects of Lactococcus lactis and astaxanthin on the growth,digestive and immune enzyme activities,immune-related gene expression and intestinal flora of Litopenaeus vannamei,and comprehensively evaluate Lactococcus lactis and astaxanthin The effect on the growth ability,digestion ability and immunity of Litopenaeus vannamei provides scientific guidance for the scientific application of two types of feed additives.A total of 4 experimental groups were set up in this article,namely the mixed group of Lactococcus lactis and basic feed(Lac280 group)with a concentration of 10~8CFU/m L,and the mixed group of astaxanthin and basic feed(ASTA group)with 250mg/kg of astaxanthin,10~8CFU/m L Lactococcus lactis and 250mg/kg of astaxanthin mixed with basic feed group(Lac280+ASTA group),40m L/kg lactic acid bacteria preparation and basic feed mixed group(PP group),and a control Group(basic feed,CK group).Other management methods are the same,the test period is 4 weeks,and the specific results are as follows:The growth index measurement of Litopenaeus vannamei showed that the weight gain of Litopenaeus vannamei in the Lac280 group was 8.8±1.73g after 4 weeks,which was significantly higher than that of the control group 5.58±0.03g(P<0.05);the weight of Litopenaeus vannamei increased in the ASTA group.The weight was 10.57±1.38g,which was significantly higher than the weight gain of the prawns in the control group;however,the weight gain of the prawns in the Lac280+ASTA group and the PP group was not significant compared with the control group.This shows that the use of Lactococcus lactis or astaxanthin alone can significantly promote the growth of Litopenaeus vannamei.It also shows that Lactococcus lactis or astaxanthin used in this article improves the growth ability of Litopenaeus vannamei compared with commercially available lactic acid bacteria preparations.The effect is better.The digestive enzyme activities of the intestinal samples of Litopenaeus vannamei were determined.The results showed that:in the first week,the amylase activities of the Lac280 group,the ASTA group and the Lac280+ASTA group were 170.33±17.97(U/mg prot),respectively.239.42±34.02(U/mg prot)and 222.61±22.83(U/mg prot),which were significantly higher than 87.56±0.39(U/mg prot)in the control group(P<0.05),while the amylase activity of Litopenaeus vannamei in the pp group was103.02±2.16(U/mg prot),no significant difference from the control group;the lipase activities of the Lac280 group and the ASTA group were 29.38±8.31(U/g prot)and28.38±8.3(U/g prot),which were significantly higher than the control group The lipase activity of the Lac280+ASTA group and the PP group were 17.82±3.7(U/g prot)and13.81±2.44(U/g prot),respectively,compared with the control group.difference.At the fourth week,the trypsin activity of Lac280 group,ASTA group,Lac280+ASTA group and pp group were 2.35±0.02(U/mg prot),3.77±0.08(U/mg prot),2.26±0.2(U/mg prot).And 1.37±0.05(U/mg prot),both were significantly higher than 0.77±0.02(U/mg prot)in the control group(P<0.05).However,the time for each additive to achieve the best effect is different.Each treatment group basically achieves the best effect in the breeding cycle in the first week,and only the ASTA group has a significant increase in trypsin activity in the fourth week.These results show that,like the growth ability,the use of Lactococcus lactis or astaxanthin alone can significantly increase the activity of digestive enzymes.However,the mixed use of Lactococcus lactis and astaxanthin has an effect on the digestive enzymes of Litopenaeus vannamei.On the contrary,it is not significant.The expression of main immune genes of Litopenaeus vannamei after 4 weeks of cultivation,and the infection test of Vibrio alginolyticus was carried out at the same time.The results showed that the immune-related genes such as pro-PO,LGBP,SOD,p EN3α,and Crustin in the Lac280 group were significantly improved(P<0.05);only the Crustin gene in the ASTA group was significantly improved(P<0.05),and for other genes No effect;the PP group had a significant effect on the expression of the above genes(P<0.05).In this paper,the experimental results of the infection of Litopenaeus vannamei with Vibrio alginolyticus HN08155 as the pathogen are:the cumulative mortality of the ASTA group,the Lac280+ASTA group and the PP group was significantly lower than that of the control group,while the cumulative mortality of Lac280 was no higher than that of the control group.difference.These results indicate that the addition of Lactococcus lactis to the feed can significantly increase the expression level of immune-related genes of Litopenaeus vannamei,but cannot improve the resistance of Litopenaeus vannamei to the infection of Vibrio alginolyticus;adding astaxanthin to the feed,although It can only increase the expression of the Crustin gene of Litopenaeus vannamei,but it can significantly reduce the infection of Litopenaeus vannamei by Vibrio alginolyticus.Therefore,pro-PO,LGBP,SOD,p EN3α,Crustin and other genes have no obvious correlation with the resistance of Litopenaeus vannamei to Vibrio infection,but Lysozyme may be related to the resistance of Litopenaeus vannamei to Vibrio alginolyticus.The high-throughput sequencing technology based on the Illumina Mi Seq platform was used to analyze the intestinal bacteria of Litopenaeus vannamei in the first and fourth weeks.The intestinal diversity of Litopenaeus prawns has no effect;at the phylum level,the dominant bacterial phyla of the five groups are Proteobacteria,Bacteroidota,Actinobacteria,and Verrucomicrons.The phylum(Verrucomicrobiota)and Firmicutes(Firmicutes),these dominant phylums accounted for more than 95%of the overall sequence;however,statistics on the microbial diversity of each group at the subordinate level found that in the first week,the control group contained higher The content of lactic acid bacteria in the Vibrio was relatively low,while the content of Vibrio in each test group was relatively low.Among them,the content of lactic acid bacteria in the Lac280 group and the Lac280+ASTA group was relatively high;in the fourth week,the content of Vibrio in the control group increased.The content of lactic acid bacteria decreased.The content of Vibrio in the Lac280 group,Lac280+ASTA group and the PP group was relatively consistent with that of lactic acid bacteria.The amount of Vibrio in the ASTA group was greater than that of lactic acid bacteria.In general,the Vibrio and lactic acid bacteria in the intestinal tract of Litopenaeus vannamei.The total amount remains the same.Because the intestinal flora is saturated,there is a competitive relationship between Vibrio and lactic acid bacteria.An increase in one side will lead to a decrease in the other.Adding lactic acid bacteria in the short term can reduce the number of Vibrio in the intestines of Litopenaeus vannamei,but it will have no effect in the long term.A scientific feeding strategy can be formulated accordingly.In summary,Lactococcus lactis can significantly promote the growth of Litopenaeus vannamei by improving the activity of its digestive enzymes.At the same time,the bacteria can also inhibit the growth of Vibrio in the intestines;astaxanthin can significantly improve Litopenaeus vannamei Growth capacity,digestive enzyme activity,total antioxidant capacity and antibacterial capacity.