| The largemouth bass(Micropterus salmoides)is an important economic breeding fish in China.The breeding production of largemouth bass has reached700,000 tons in 2021.At present,the feed preparation technology is still limited by many factors,which affects the green and healthy development of the industry.Theories such as "antibiotic-free farming,green ecology and sustainable development" are deeply rooted in the hearts of the people.Natural medicinal plants with green,wide resources and rich bioactive components have the effect of enhancing animal liver and intestinal function and regulating intestinal flora,which has attracted wide attention from the industry.Therefore,this study took largemouth bass as the experimental object to explore the improvement effects of four medicinal plants,including Folium Mori,Perilla frutescens,Illicium verum and Artemisia annua,on the health of largemouth bass from the perspectives of growth performance and liver and intestinal health,and to clarify the protective effects of medicinal plants on fish health.In order to provide a new way for the development of green and high quality compound feed and healthy breeding of largemouth bass.(1)The effects of three medicinal plant extracts on the growth and health of the largemouth bass(Micropterus salmoides)To explore the application effect of different medicinal plants on largemouth bass diet.In this experiment,four kinds of experimental diets with isonitrogen(49.41%protein)and isolipid(11.36% crude fat)were arranged,and the basal diet was used as the control group(CON),and 0.075% extracts of Perilla frutescens(PFE),Illicium verum(IVE)and Artemisia annua(AEE)were added,respectively.The juvenile largemouth bass with an average weight of(18.20 ± 0.20)g were fed for 80 days with three replicates per group(tank volume 180 L,25 fish/tank).The results showed that IVE and AEE groups significantly improved the growth performance of largemouth bass,and decreased the liver lipid content and liver body ratio(P < 0.05).The addition of IVE and AEE could increase the liver antioxidant capacity(CAT,GSH-PX,T-SOD)and anti-inflammatory cytokines(il-10,tgf-β)mRNA expression levels,while the serum transaminase activity decreased.The addition of PFE and AEE increased the contents of serum albumin and globulin,while the contents of IgM and complement C4 in IVE group were higher than those in other groups(P < 0.05).At the same time,IVE and AEE could improve the intestinal tissue structure of fish,upregulate the relative expression levels of occuldin-1 and claudin-1,and reduce the contents of D-lac and LPS in serum(P < 0.05).In addition,IVE and AEE groups significantly increased theα-diversity of intestinal flora,inhibited the abundance of potentially harmful bacteria(Aeromonas and Shigella),and increased the abundance of probiotics(Lactobacillus)(P< 0.05).In the acute challenge experiment,when all the CON group died,the cumulative survival rate of the IVE group was 26.6%.In conclusion,IVE and AEE enhance the liver function and intestinal physical barrier of largemouth bass,and then promote the growth of fish.Considering all the indicators,IVE has the best immune effect and has the potential to be developed as a medical-plant feed additive to improve fish health.(2)Effects of mulberry leaves of different processes on growth and health of largemouth bass(Micropterus salmoides)In order to evaluate the application effects of mulberry leaves with different processes in the diet of largemouth bass,this experiment used the basic diet as the control group,and added the general mulberry leaf powder(MG),broken wall mulberry leaf powder(MB)and mulberry leaf extract(ME)based on 4% raw material,respectively,to prepare four experimental diets of isonitrogenous and isolipid.The largemouth bass with an average weight of(8.72 ± 0.03)g were divided into 12 tanks(180L volume,30 tail/tank)with three replicates per group and fed for 70 days.The results showed that compared with the control group,MG treatment had no effect on the growth performance of largemouth bass,while the ME group had a certain promotion effect(P > 0.05),while the MB group significantly increased the final body weight(FBW)and specific growth rate(SGR),and decreased the fish body lipid and lipid deposition rate of largemouth bass(P < 0.05).After mulberry leaves were added,the liver color was ruddy,the number of liver cells increased,the vacuolization rate decreased significantly,and the content of lipid droplets was less in MB group.The contents of glycogen and lipid in liver and the contents of glucose,VLDL,TG and TC in serum were also decreased(P < 0.05).Mulberry leaf supplementation increased the mRNA expression levels of glycolysis(gk,pfk)and lipolysis(cpt1,lpl),and down-regulated the expression levels of gluconeogenesis(g6pc)and Fat synthesis(acc,fac)genes in the liver of largemouth bass(P < 0.05).Mulberry leaves of different processes can increase the activity of GSH-PX and CAT and the expression of related genes in the liver of largemouth bass,and the content of malondialdehyde and the activity of AST(P < 0.05).Compared with the control group,the mRNA expression of pro-inflammatory cytokines(il-8,tnf-α)was significantly down-regulated,and the mRNA expression of anti-inflammatory cytokines(il-10,tgf-β)was increased in BM group(P < 0.05).In addition,MB treatment inhibited hepatocyte apoptosis in largemouth bass and reduced intestinal dysbiosis by limiting the development of Gram-negative bacteria.In conclusion,mulberry leaves can improve liver health by regulating glucose and lipid metabolism,inhibiting cell apoptosis,and improving liver health.The biological potency of mulberry leaves with different processes is different,and the effect of broken wall mulberry leaf is the best. |
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