Effects Of Earthworm Peptide On Growth Performance,Immune Function And Antioxidant Capacity Of Procambarus Clarkii

Procambarus clarkii is an important freshwater economic shrimp in China.After years of continuous development,the market demand for P.clarkii is growing.Its breeding practitioners continuously improve the density of breeding and pursue high mu yield.At the same time,diseases occur frequently.The long-term use of antibiotics is easy to cause drug resistance and other problems,and the control effect is also poor.Therefore,it has become a research hotspot to select appropriate feed additives to improve animal production performance and anti-stress ability to the environment,and reduce the incidence of disease.Earthworm peptide is a kind of earthworm hydrolysate in vitro,which is rich in small peptides,free amino acids,etc.because of its wide source and low price,and earthworm has a good effect on other aquatic animals.However,the application of earthworm peptide in P.clarkii has not been studied.This experiment was conducted to investigate the effects of earthworm peptide on growth performance,antioxidant capacity and immune function of P.clarkii.The juvenile P.clarkii(2.5 ± 0.5 g)with the similar body weight were randomly divided into 6 groups,with 3 repetitions in each group and 20 shrimp in each tank.Earthworm peptides of 0.0,0.5,1.0,2.0,3.0 and 4.0 g/kg were added to the basal diet for 8 weeks.No feeding shall be conducted 24 hours before sampling after breeding.Record the number and weight of shrimp surviving in each tank,obtain hemolymph samples,and then immediately dissect the hepatopancreas and intestinal tissues on ice for backup.The effects of earthworm peptide on the growth performance,antioxidant function and immune ability of P.clarkii were systematically evaluated from the growth performance,intestinal digestive enzyme activity,antioxidant gene expression,midgut morphology,muscle nutrients,serum biochemical indicators,hepatopancreas antioxidant capacity,immune enzyme activity,immune related gene expression and other indicators.The purpose of this study was to find out the appropriate addition of earthworm peptide in the diet of P.clarkii,and to provide basis for feed production practice.The existing test results are as follows:1、After adding earthworm peptide to the diet for 8 weeks,it was found that the weight gain rate and specific growth rate of P.clarkii increased significantly at the addition of 2.0 and 3.0 g/kg(P < 0.05).The linear analysis of earthworm peptide addition,weight gain rate and feed coefficient showed that the appropriate addition in the diet was 3.15-3.58 g/kg.In addition,earthworm peptide and P.clarkii muscle nutrients,intestinal digestive enzyme activity were not significantly affected(P >0.05).Earthworm peptide had no significant effect on the duplicature length of midgut of P.clarkii(P>0.05),and the duplicature width was significantly increased in the diet supplemented with earthworm peptide of 2.0-4.0 g/kg(P<0.05).2、After adding earthworm peptide to the basic diet,the activities of antioxidant enzymes in the intestine and hepatopancreas of P.clarkii were significantly increased.SOD and cat in intestine and hepatopancreas increased at first and then decreased.The activity of SOD in hepatopancreas and intestine increased significantly in the group with earthworm peptide addition of 1.0-3.0 g/kg(P<0.05);The intestinal CAT activity reached the maximum when earthworm peptide was added at 2.0 g/kg,and the hepatopancreas CAT activity reached the maximum when earthworm peptide was added at 2.0 and 3.0 g/kg(P<0.05).The intestinal GSH PX activity reached the maximum when earthworm peptide was added at 4.0 g/kg,and the hepatopancreas GSH PX activity reached the maximum when earthworm peptide was added at 2.0-3.0g/kg(P<0.05).In addition,the midgut antioxidant genes(hsp70,fer,mt)increased first and then decreased.The relative expression of HSP70 was the highest when earthworm peptide was added to the diet at 2.0-3.0 g/kg(P < 0.05);The relative expression of fer was the highest when earthworm peptide was added to the diet at 3.0g/kg(P < 0.05);The relative expression of MT was the highest when earthworm peptide was added to the diet at 2.0 g/kg(P<0.05).3、The addition of earthworm peptide to the diet of P.clarkii could significantly affect the content of TP in serum.The content of TP in serum was significantly higher than that in the control group when the amount of earthworm peptide was 2.0-3.0 g/kg,but significantly lower when the amount of earthworm peptide was 4.0 g/kg(P <0.05).ALT in serum was significantly higher than that in control group(P<0.05).Got in serum was significantly higher than that in control group when earthworm peptide was added at 3.0-4.0 g/kg,and significantly lower than that in control group when earthworm peptide was added at 0.5-2.0 g/kg(P<0.05).With the increase of earthworm peptide in diet,LZM activity in hepatopancreas did not change significantly(P>0.05),while ACP and AKP activities increased gradually.Among them,ACP activity was significantly higher than other groups when earthworm peptide was added to the diet at 2.0-4.0 g/kg,and AKP activity reached the maximum when earthworm peptide was added to the diet at 4.0 g/kg(P<0.05).The relative expression of three immune genes in hepatopancreas showed a trend of increasing first and then decreasing.The relative expression of crustin and alf was the largest when earthworm peptide was added to the diet at 3.0 g/kg,and the relative expressio of lectin was the largest when earthworm peptide was added to the diet at 2.0-3.0 g/kg.At the end of the experiment,a 5-day bacterial infection experiment was carried out.It was found that 120 hours after Aeromonas veronii infected P.clarkii,the survival rate of the diet supplemented with earthworm peptide was higher than that of the control group,and the highest survival rate was in the diet supplemented with earthworm peptide of 3.0 g/kg.