Effects Of Yeast Hydrolysate On Growth Performance,immune Function And Intestinal Flora Of The Red Swamp Crayfish (Procambarus Clarkii)

Procambarus clarkii plays an important role in freshwater economic shrimp culture in China.At present,the nutritional requirements of P.clarkii in high-density intensive culture are basically met by feeding artificial diets.If the diet formulation is not reasonable,the growth and development of crayfish and non-specific immunity will be adversely affected,and a variety of pathogenic bacteria will cause large-scale disease of crayfish.At present,there is a lack of treatment measures for P.clarkii disease.Mainly through strengthening daily management,nutrition regulation and other means to prevent the occurrence of diseases.Therefore,it is very important to seek high quality functional feed additives to maintain the growth and development of aquatic animals and normal physiological function.Yeast hydrolysate is a new type of high-quality feed additive prepared by a series of complex processes using fresh Saccharomyces cerevisiae as raw material,which can promote animal growth and development,enhance digestion and antioxidant capacity,improve immunity and maintain biological intestinal health.The field of aquaculture has made extensive use of yeast hydrolysates,but no studies on crayfish have been published.Consequently,The aim of this study was to investigate the effects of different concentrations of yeast hydrolysate on growth performance,digestive capacity,antioxidant capacity,non-specific immunity and intestinal flora of P.clarkii.In this study,300 healthy juvenile shrimp with an average body weight of(6.43 ± 0.55)g were randomly divided into 5 groups with 3 replicates in each group,and the culture density was 20 shrimp/tank.The amount of yeast hydrolysate in the basal diet was 0(control group),0.50%,1.00%,2.00% and 4.00%,respectively,and the feeding experiment lasted for 8 weeks.At the end of the experiment,the growth,digestion,antioxidant and immune indexes of crayfish were detected.The effects of yeast hydrolysate on the survival,growth,antioxidant defense system,non-specific immunity and intestinal flora of juvenile crayfish were analyzed.It aims to improve the feed preparation and healthy culture of P.clarkii,provide scientific basis for modern aquaculture and the use of feed additives,and provide a theoretical basis for yeast hydrolysate to improve the growth,digestion,antioxidant and non-specific immunity of P.clarkii.The results of this experiment are as follows:1.Dietary supplementation of 1.00% to 4.00% yeast hydrolysate had significant effects on the growth indexes of P.clarkii(P<0.05),among them,the survival,last body weight,body length and hepatopancreatic index of crayfish in the group with 2.00%yeast hydrolysate were the highest,and the weight gain rate and specific growth rate of crayfish with 1.00% yeast hydrolysate added to feed were the highest.The crude protein content of whole shrimp supplemented with 1.00% yeast hydrolysate was significantly higher than that of other groups(P<0.05).The crude protein and crude fat contents of muscle of crayfish in 2.00% yeast hydrolysate group were significantly increased(P<0.05).Compared with the control group,the addition of yeast hydrolysate to feed significantly increased the activity of stomach tissue and hepatopancreatic digestive enzyme activity of crayfish(P<0.05),the activity of stomach tissue and hepatopancreatic amylase and protease was the highest in the group with 2.00% yeast hydrolysate,and the activity of stomach tissue and hepatopancreatic lipase was highest in the group with 1.00% yeast hydrolysate.2.Compared with the control group,with the increase of the content of yeast hydrolysate in the diet,the intestinal folds of P.clarkii were significantly increased and the distribution was orderly.The 2.00% yeast hydrolysates supplementation group had the largest length and width of intestinal folds(P<0.05),increased intestinal folds,and decreased intestinal space,which could improve intestinal morphology and promote intestinal growth and development.In 0.50%-2.00% yeast hydrolysate groups,the intestinal cells were closely arranged and the connective tissue was numerous,and the density was higher than that of the control group.The number of yolk granules and peripheral follicular cells increased in 2.00% and 4.00% yeast hydrolysate groups.3.After adding yeast hydrolysate to the diet,the antioxidant properties and non-specific immunity of crayfish were significantly improved(P<0.05).The contents of total protein(TP)and albumin(ALB)in serum of 2.00% yeast hydrolysate supplemented group were significantly higher than those of control group(P<0.05),and the activities of serum alanine aminotransferase(ALT)and aspartate aminotransferase(AST)were significantly lower than those of control group(P<0.05).The antioxidant capacity of P.clarkii supplemented with yeast hydrolysate was significantly higher than that of the control group(P<0.05).The hepatopancreas CAT activity,T-SOD activity and T-AOC ability of 2.00% yeast hydrolysate added group were the highest,and the hepatopancreas GSH-PX activity of 1.00% yeast hydrolysate added group was the highest.The content of MDA in hepatopancreas was the lowest in the 2.00% yeast hydrolysate group.Compared with the control group,the 0.50%-4.00% yeast hydrolysate supplementation groups had significantly increased AKP,ACP and LZM activities of hepatopancreas(P<0.05).The highest AKP and ACP activities were observed in 2.00% yeast hydrolysate supplementation group,and the highest LZM activity was observed in 1.00% yeast hydrolysate supplementation group.4.Yeast hydrolysate can improve the gut microbiota structure of P.clarkii.High-throughput 16 s r DNA sequencing was used to analyze the composition and function of intestinal microbial structure in the control group and 2.00% yeast hydrolysate addition group.The results showed that the sequencing coverage rates were all more than 99.95%.There was no significant difference in intestinal microbial richness index and diversity index between the yeast hydrolysate groups(P>0.05),but the composition of intestinal flora was changed.At the phylum level,the top six dominant phyla of both groups were Proteobacteria,Tenericutes,Firmicutes,Bacteroidetes,Actinobacteria and TM 7,but the proportion was different.Compared to the control group,yeast hydrolysate group phase Proteus phylum abundance is reduced,increased abundance of Firmicutes and Bacteroides phylum.In the control group,the dominant genera were Anaerorhabdus(10.60%),Aeromonas(8.55%),Dysgonomonas(6.20%),Shewanella(1.66%),Pseudomonas(1.50%)and Rhodobacter(1.10%).The dominant genera in the yeast hydrolysate group were Anaerorhabdus(14.90%),Bacteroides(12.36%),Shewanella Shewanella(5.76%),Dysgonomonas(5.04%),Rhodobacter(4.92%),Acinetobacter(4.18%).According to the KEGG functional pathway abundance map,the relative abundance of differential genes is mainly concentrated in four metabolic pathways: carbohydrate metabolism,amino acid metabolism,cofactor and vitamins metabolism,and metabolism of terpenoids and polyketones.In conclusion,dietary supplementation of 2.00% yeast hydrolysate significantly improved the growth performance and digestive enzyme activities of P.clarkii.The antioxidant capacity of P.clarkii was improved when the amount of yeast hydrolysate was 1.00% to 2.0%.2.00% yeast hydrolysate significantly improved the immune status of crayfish and optimized the structure of intestinal micro flora.It is suggested that2.00% yeast hydrolysate should be added to the diet of young crayfish.