Effects Of Eucommia Extract,Tea Polyphenols And Compound Chinese Herbs On Growth,Antioxidant Capacity And Disease Resistance Of Larimichthys Crocea

Larimichthys crocea is the most productive marine fish in China.However,with the expansion of aquaculture scale,the disease of L.crocea seriously restricts the sustainable development of L.crocea aquaculture industry.Natural plant extracts have the effects of promoting growth,improving disease resistance,increasing feeding rate and enhancing efficacy.They are commonly used as immune additives,growth promoters,vaccine adjuvants,etc.,and play an important role in aquaculture production activities.This study uses L.crocea as the research object to investigate the effects of three combinations of Eucommia extract,Eucommia extract+tea polyphenols and Eucommia extract+Mixed powder(main components:Pueraria powder,Gynostemma pentaphyllumh,licorice)on the growth,disease resistance,antioxidant capacity,intestinal microbial composition and bile acid enterohepatic circulation of L.crocea at a certain concentration,and to explore the different effects of three combinations on L.crocea.This study is divided into three parts:In order to explore the effects of Eucommia ulmoides,tea polyphenols and compound Chinese herbs on the growth,liver and intestine of juvenile L.crocea.The experiment was divided into four groups:Esu group(0.2%Eucommia extract),Tea group(0.2%Eucommia extract+0.05%tea polyphenols),Mix group(0.2%Eucommia extract+0.2%mixed powder)and Nor group(control group).The juvenile L.crocea(16.91±0.04 g)was cultured in the cage for 30 days(length×widthxheight:1 m× 1 m× 2 m),and the artificial infection experiment of Pseudomonas plecoglossicida was carried out for 16 days.The effects of different combinations on the growth index,feed coefficient,survival rate of challenge infection,immune gene expression(MCHII-α,IL-10,Mx),liver transcriptome and intestinal microbial composition of L.crocea were analyzed based on the results of culture and artificial challenge.The results showed that:1.the survival rate and growth performance of juvenile L.crocea fed with three combinations were not significantly different from those of the Nor group(P>0.05);2.Eucommia extract significantly improved the disease resistance of juvenile L.crocea(P<0.05).In the experiment of Pseudomonas plecoglossicida challenge infection,the relative protection rate of Esu group reached 64.32%,and the relative protection rates of Tea group and Mix group decreased to 33.97%and 29.46%,respectively,but still significantly higher than that of Nor group(P<0.05).3.Compared with Nor group,Esu group affected the functional genes related to endoplasmic reticulum and alcohol metabolism in liver,while Tea group and Mix group affected the functional genes related to metabolic pathway and endoplasmic reticulum,respectively.4.The combination of Eucommia extract+tea polyphenols affected the proportion of Firmicutes and Bacteroidetes in the intestine of juvenile L.crocea.The ratio of the two in Tea group(0.15)was significantly higher than that in Nor group(0.03)(P<0.05),but there was no significant difference between Esu group and Mix group and Nor group(P>0.05).In order to explore the effects of Eucommia ulmoides.tea polyphenols and compound Chinese herbs on the growth,antioxidant capacity and intestinal tract of L.crocea.The experiment was divided into four groups:Esu S group(0.2%Eucommia extract+4%soybean oil),Tea S group(0.2%Eucommia extract+0.05%tea polyphenols+4%soybean oil)and Mix S group(0.2%Eucommia extract+0.2%mmm mixed powder+4%soybean oil)and S group(4%soybean oil).The(184.66±10.72)g was cultured in cages for 20 days(length×width×height:1.5 m× 1.5 m× 3 m),and samples were collected at 10 days and 20 days,respectively.The results showed that:The survival rate and growth performance of L.crocea fed with three combinations had no significant effect compared with the control group(P>0.05).The content of malondialdehyde(0.37 nmol/mg)in liver of L.crocea in Esu S group was significantly lower than that in S group(1.07 nmol/mg)(P<0.05),and the content of bile acid in intestine(29.62 μmol/g)was also significantly lower than that in S group(37.59μmol/g)(P<0.05).but there was no significant difference between Esu S group and S group after 20 days(P>0.05).3.After 10 days of culture,the antioxidant capacity of Tea S group was not significantly different from that of S group(P>0.05).but after 20 days,the content of malondialdehyde in serum and liver was 1.33 and 3.69 times higher than that of S group,respectively(P<0.05).The combination of Eucommia extract and mixed powder for 10 days reduced the oxidative stress level of L.crocea.The serum malondialdehyde content of Mix S group was significantly lower than that of S group by 48%(P<0.05).At the same time,the intestinal bile acid content also decreased by 56%.the difference was significant(P<0.05).and there was no significant difference at 20 days(P>0.05).To explore the effects of Eucommia ulmoides,tea polyphenols and compound Chinese herbs on the growth and antioxidant capacity of L.crocea reared with oxidized oil.The experiment was divided into 5 groups:Esu OS group(0.2%Eucommia extract+4%oxidized soybean oil),Tea OS group(0.2%Eucommia extract+0.05%tea polyphenols+4%oxidized soybean oil)and Mix OS group(0.2%Eucommia extract+0.2%mixed powder+4%oxidized soybean oil),S group(4%soybean oil)and OS group(4%oxidized soybean oil).The L.crocea(184.66±10.72)g was cultured in the cage for 20 days,and the samples were taken after the culture.The results showed that:1.The growth performance of L.crocea fed with 4%oxidized oil diet was significantly reduced.The weight gain rate and specific growth rate of OS group were 46%and 41%lower than those of S group(P<0.05),and the feed coefficient was significantly increased by 92%(P<0.05).At the same time,the level of oxidative stress was increased and the antioxidant capacity was decreased.The serum malondialdehyde content in OS group(25.62 nmol/mg)was significantly higher than that in S group(13.18 nmol/mg)(P<0.05).The total bile acid content of liver in OS group(7.09μmol/g)was significantly higher than that in S group(5.06 μmol/g)(P<0.05).2.Under the condition of feed containing oxidized oil,the growth performance of L.crocea could be restored by adding Eucommia extract,and the metabolic excretion of intestinal bile acid was promoted.The content of bile acid in the intestine of Esu OS group(16.46 μmol/g)was significantly lower than that of OS group(34.20 μmol/g)(P<0.05).3.Eucommia extract+tea polyphenols could restore the enterohepatic circulation of bile acids in L.crocea fed with oxidized oil feed to the level of S group,but had no significant effect on growth performance,antioxidant capacity and oxidative stress level(P>0.05).4.Eucommia extract+mixed powder could significantly reduce the oxidative stress level of L.crocea fed with oxidized oil feed.The malondialdehyde content in serum and liver of Mix OS group(17.60 nmol/mg and 0.40 nmol/mg)was significantly lower than that of OS group(25.62 nmol/mg and 1.07 nmol/mg)(P<0.05),and returned to the level of S group.Based on the above results,it is found that.The addition of 0.2%Eucommia extract to the feed had no significant effect on the growth of L.crocea,but it could restore the growthdamage and liverdamage caused by oxidized oil,and effectively promote thedisease resistance of L.crocea.0.2%Eucommia extract+0.05%tea polyphenols can adjust the changes of microbial composition in the intestine of L.crocea,but it will cause the increase of oxidative stress level.0.2%Eucommia extract+0.2%mixed powder can effectively reduce the oxidative stress level of L.crocea.