Effects Of Different Dietary Protein Levels On Growth Performance,Biochemical Composition,Digestive Ability And Protein Metabolism Of Eriocheir Sinensis Under Rice-crab Culture Systems

Protein is the most critical nutrient in feed,which has a very important impact on the growth of aquatic animals.The accurate protein nutritional needs in feed are the prerequisites for accurate nutrition and accurate feeding.At present,the cultivation of crabs in rice fields in Jilin Province is still dominated by extensive farming.The feeding and management of rice crabs mainly refer to the pond model.However,there are huge differences in the breeding cycle and breeding environment of Chinese mitten crab(Eriocheir sinensis,also known as river crab)under the two models.Therefore,the demand for protein of Chinese mitten crab is not the same,and there is also a lack of matching artificial compound feed for rice crabs,which is extremely unfavorable for further expanding the scale of crab farming in northern rice fields and forming a characteristic fishing rice industry cluster.With the continuous promotion and development of rice-crab symbiosis model,the demand for special compound feed is increasing,and the precise nutritional needs of rice-crab feed protein is an urgent industrial problem to be solved.Therefore,this experiment was conducted under rice-crab culture systems.The Chinese mitten crab(6.74±0.25 g)was used as the test object,and a three-month feeding experiment was conducted in 15 rice fields with the same area(996 m~2)and geographical environment.Each 3 rice fields(3 replicates)were fed a feed to study the effects of five different protein levels(20%,25%,30%,35%and 40%,recorded as P1-P5)on the growth performance,edible part biochemical composition,digestive ability and protein metabolism of female and male crabs.The results are as follows:1.Effects of dietary protein level on growth performance of Chinese mitten crab in rice field culture modeFemale crabs:BW,WGR and SGR all reached the maximum in P5 group,and P4 and P5 groups were significantly higher than other groups(P<0.05);h SI reached the maximum value in P5 group,and HSI in P3,P4 and P5 groups was significantly higher than that in other groups(P<0.05).The expression of IGF2 mRNA in muscle of P2 group was significantly increased(P<0.05).Male crab:BW,WGR and SGR all reached the maximum in P5 group,and P1 and P2groups were significantly lower than other groups(P<0.05);h SI in P5 group was significantly higher than that in other groups(P<0.05).The GSI of P3 group was significantly higher than that of other groups(P<0.05).The expression of IGF2,CHI and EcR mRNA in muscle of P1 group was significantly decreased(P<0.05),and the expression of RXR mRNA was significantly increased in P3 group.2.Effects of dietary protein level on the biochemical composition of the edible part of Chinese mitten crab in rice field culture modeFemale crabs:The crude protein content of hepatopancreas in P2,P3 and P5 groups was significantly higher than that in P1 group(P<0.05).The content of crude protein in muscle decreased significantly in P5 group(P<0.05),and the content of crude fat increased significantly in P5 group.Male crab:hepatopancreas crude protein content decreased significantly in P2 group(P<0.05);the crude protein content of muscle in P5 group was significantly higher than that in P1 and P2 groups(P<0.05).The crude protein content of gonad in P5 group was significantly higher than that in P4 group(P<0.05).3.Effects of dietary protein level on digestive ability of Chinese mitten crab in rice field culture modeFemale crabs:the activities of trypsin,amylase and lipase in hepatopancreas were significantly increased in P3 group(P<0.05),and the expression of TGL mRNA in intestine was significantly increased in P3 group(P<0.05).The expression of IL and TRYP mRNA was significantly increased in P2 and P4 groups(P<0.05),and the expression of CTRB1mRNA was significantly increased in P2 group(P<0.05).Hepatopancreas:TGL,TRYP and CTRB1 mRNA expression were significantly increased in P5 group(P<0.05),and PRS44 mRNA expression was significantly increased in P4 group(P<0.05).Male crab:hepatopancreas trypsin activity was significantly increased in P5 group(P<0.05),and lipase and amylase activities were significantly decreased in P3,P4 and P5 groups(P<0.05).Intestinal:TGL,IL,TRYP,PRS44,CTRB1 mRNA expression were significantly increased in P2 group(P<0.05);hepatopancreas:TGL mRNA expression was significantly increased in P3 group(P<0.05),TRYP and CTRB1 mRNA expression were significantly increased in P2 group(P<0.05).4.Effects of dietary protein level on protein metabolism of Chinese mitten crab in rice field culture modeFemale crabs:GOT activity and TG content in hepatopancreas were significantly increased in P3 group(P<0.05).Serum GOT activity and TG content were significantly increased in P4 group(P<0.05).The expression of mTOR and S6K1 mRNA in hepatopancreas was significantly increased in P4 group(P<0.05).The expression of S6mRNA in P3 group was significantly higher than that in other groups(P<0.05).The expression of 4E-BP1 mRNA was significantly increased in P5 group(P<0.05).Male crabs:GOT and TC contents in hepatopancreas were significantly increased in P4group(P<0.05),and GOT activity and TC content in serum were significantly increased in P1 group(P<0.05).The expression of mTOR mRNA in hepatopancreas was significantly increased in P3 group,and the expression of S6K1 and S6 mRNA was significantly increased in P2 group(P<0.05).Too high or too low dietary protein levels will adversely affect the growth,digestion and protein metabolism of Chinese mitten crab under the mode of rice-crab culture in Jilin Province,.Based on the growth data,other indicators and economic factors,it is recommended that the appropriate dietary protein level for female crabs is 25%-30%,and the appropriate dietary protein level for male crabs is 30%-35%.