Comparative Study On The Growth,Nutritional Quality,and Digestive Capacity Of Chinese Mitten Crab (Eriocheir Sinensis) Between Liaohe And Yangtze River Strains In Paddy Farming Environment

Eriocheir sinensis is widely distributed,reaching as far north as Heilongjiang and south as Fujian.Chinese mitten crab is the largest cultured crab species in China,and is an important aquatic economic animal with high economic and nutritional value.The Chinese mitten crab can be mainly divided into two strains: the Yangtze crab and the Liaohe crab.The northern part mainly breeds the Liaohe crab,while the southern part mainly breeds the Yangtze crab.With the problems of breeding environment and breeding mode,the milk sickness of Liaohe crabs in the north is extremely serious,which seriously reduces the survival rate and economic benefits of breeding,while Yangtze crabs in the south rarely get sick.In addition,Yangtze crabs are large in size and have high market value.Therefore,Yangtze crabs are selected to replace Liaohe crabs in the north for breeding,but further research is needed to prove the solution to the milk sickness of northern crabs.Therefore,this experiment takes Liaohe and Yangtze crabs as the research objects.On the first day(June 8th,T1 stage),15 th day(June 23 rd,T2 stage),30 th day(July 8th,T3 stage),44 th day(July 22 nd,T4 stage),57 th day(August 4th,T5 stage),72 nd day(August 19 th,T6 stage),81 st day(August 28 th,T7 stage)On the 95 th day(September 11 th,T8stage),60 crab samples(30 females and 30 males each)were randomly captured from each paddy field,and their growth performance,nutritional quality of edible parts,digestive function and other related indicators were tested to explore the differences in growth and nutritional quality between the two types of crabs at different growth stages in the symbiotic environment of rice crabs in the north,providing theoretical basis and reference for the application and promotion of crab farming in Northeast rice fields.The following conclusions are drawn:(1)Growth and Variation of Liaohe Crab and Yangtze Crab at Different Growth Stages in Paddy Field EnvironmentMale crab: the average weight of Yangtze crab was 125.18±2.35 g,hepatopancreatic index and gonadal index reached their maximum values at T2 and T8 stages,respectively.That was significantly higher than those in other groups(P<0.05).Both the weight gain rate and the specific growth rate reach their maximum values in the T8 stage.Average weight of Liaohe crab was 122.61±3.82 g,hepatopancreatic index and gonadal index reached their maximum values at T3 and T8 stages,respectively(P<0.05).Both the weight gain rate and the specific growth rate reach their maximum values in the T3 stage(P<0.05).Female crab: average weight of Yangtze crab was 92.99±2.88 g,T2 stage had the maximum values of hepatopancreatic index,weight gain rate and the specific growth rate(P<0.05).Gonadal index reached their maximum values at T8 stages(P<0.05).Average weight of Liaohe crab was 82.25±1.21 g,the maximum specific growth rate and weight gain rate were observed during the T3 period(P<0.05).The hepatopancreatic index showed a trend of first increasing and then decreasing,reaching its maximum value during the T5 period,the gonadal index reaches its maximum value during the T8 period(P<0.05).(2)Changes in Nutritional Quality of Liaohe Crab and Yangtze Crab at Different Growth Stages in Paddy Field EnvironmentNutritional quality: the gonadal crude fat content of Yangtze male crab was significantly lower than Liaohe male crab(P <0.05).The muscular crude protein content of Yangtze female crab was significantly higher than Liaohe crab(P <0.05).The hepatopancreatic crude fat content of Yangtze female crab was significantly higher than Liaohe female crab(P <0.05).The ovarian crude protein content of Yangtze female crab was significantly higher than Liaohe crab(P<0.05).Amino acid composition: the level of ∑TAA and ∑EAA in Liaohe male crab muscle significantly higher than that of Yangtze crab,the hepatopancreatic methionine level of Yangtze male crab significantly higher than that of Liaohe male crab,the level of valine in Yangtze male crab gonad significantly higher than that of Liaohe crab(P<0.05).Liaohe female crab had the higher level of ∑TAA and ∑NEAA in the muscles(P<0.05).Liaohe female crab also had the higher level of ∑TAA in the ovary(P<0.05).Fatty acid composition: the muscles C18:2n6c,C18:3n3,C20:3n6 level of Liaohe male crabs were significantly higher than that of Yangtze crabs,the muscles C20:2,C20:5n3(EPA),n-3 PUFA,n3/n6 level of Yangtze male crabs were significantly higher than that of Liaohe male crabs(P<0.05).Liaohe male crab had the higher level of ∑SFA and DHA/EPA in the gonads than that of Yangtze crabs(P<0.05).The ovarian ∑PUFA,∑n-3PUFA and n3/n6 level of Yangtze female crabs were significantly higher than that of Liaohe female crabs,on the contrary,Liaohe female crab had the higher level of ∑SFA(P<0.05).(3)Digestive Physiological Changes of Liaohe Crab and Yangtze Crab at Different Growth Stages in Paddy Field EnvironmentMale crab: the high expression levels of IL,TGL,CTRB1,PRS44,and TRYP m RNA in the hepatopancreas of Yangtze crab and Liaohe crab were at T6-T8 stages.Female crabs: the high expression levels of IL,TGL,CTRB1,PRS44,and TRYP m RNA in the hepatopancreas of Yangtze crab and Liaohe crab were at T4-T8 stages.Under the experimental conditions,survival rate of Liaohe crab was higher than that of Yangtze crab.However,average weight of Yangtze crab was higher than that of Liaohe crab.Gonadal index reached their maximum values at T8 stages.The rapid development stage of the Liaohe crab was July.The rapid development stage of Yangtze male crab was middle of July to middle of September,the rapid development stage of Yangtze female crab was June to August.The gonadal development of male and female crabs differs from each other.The Yangtze male crab and Liaohe male crab(T4 stage)are earlier than the Yangtze female crab(T5 stage)and Liaohe female crab(T6 stage).Considering the approximate composition,Liaohe male crab was better than Yangtze male crab,and Yangtze female crab was better than Liaohe female crab.For amino acid,Liaohe crab was better than Yangtze crab.Yangtze crab and Liaohe crab had the similar fatty acid results of the edible tissues.Whether in the Yangtze crab or the Liaohe crab,the m RNA expression levels of protein and lipid utilization related genes in male(T7-T8)and female crabs(T4-T8)were increased,indicating that these periods are the periods of rapid accumulation of nutrients in both types of crabs,at which time the digestive ability is strongest.