Study On The Feeding Habit And Intestinal Microbes Of Eriocheir Sinensis In The Yangtze River Estuary

Eriocheir sinensis belongs to Grapsidae,Decapoda,Malacostraca,which are migratory crustaceans.In recent years,the resources of E.sinensis declined sharply due to human overfishing,reclamation activities and habitat degradation in the Yangtze River Estuary.Spawning period is the key stage to determine E.sinensis population resources as the most important life stage in the life history.In this study,that were studied by gastric material analysis and high-throughput sequencing of the dietary composition and differences of the female crabs before and after spawning in the Yangtze River Estuary,and the diversity of intestinal microbes was studied,Providing reference for the habitat restoration and resource conservation of E.sinensis,enriching its basic biology knowledge.1.Dietary and feeding intensity of female E.sinensis in the Yangtze River Estuary during migratory periodTo study the feeding habits and nutritional structure of female E.sinensis in the Yangtze River Estuary during reproductive migration,the feeding composition,feeding intensity and trophic level were analyzed by the gastric contents of female E.sinensis which were collected from October 2017 to April 2018.The results showed that the feeding rate,food fullness index and mean gastric fullness index of female E.sinensis had obvious monthly changes.The indexes before the spawning were highest in October-November(autumn)and lowest in December-February(winter).After the female crab is spawning,the indicators are the lowest in December-February(winter)and the highest in March-April(spring).The female crabs in the migratory stage have various feed sources including Aquatic plants,Algae,Crustacean,Polychaeta,Piscium,Mollusca,Echinodermata,Eggs,Detritus etc,belonging to omnivorous aquatic animals.Algae,Detritus and Crustacean were the main diets of the female crab before spawning,and the frequency percentage were 68.13%,54.76%,19.05% respectively.Algae,Detritus and Aquatic plants were the main diets for female crabs after spawning,and the percentage of frequency were 70.35%,73.91%,25.39%respectively.There was a significant difference in food composition of female crabbefore and after spawning(?2=21.57,P<0.05).The food composition that contributed most to the differences were detritus(?2=8.32),crustacean(?2=5.49)and aquatic plants(?2=4.02).The trophic level of female crabs before and after spawning were3.60 and 3.10,the average trophic level was 3.35.Thus,the crabs belong to the third trophic level animals.The results showed that the female crabs in the migratory stage did not stop eating before and after spawning,and the food sources were diverse,belonging to the third trophic level carnivorous animals.In the habitat restoration technology,according to the feeding composition of female crabs in the migratory stage,the bait selection and delivery were carried out to meet the energy requirements of mating,spawning and hatching of E.sinensis,and the production rate and hatching rate were improved.2.Study on the feeding habits of female E.sinensis based on high-throughput sequencing techniqueIn this study,high-throughput sequencing was used to study the feeding habits of E.sinensis in the Yangtze River Estuary.The results showed that the high-quality sequences of 37 samples were between 53288 and 90598.Through cluster analysis of423 OTU,food types were obtained including Bacillariophyta,Chlorophyta,Pyrrophyta,Chrysophyta,Rhodophyta,Advanced plants,Piscium,Crustacea,Granulifusus kiranus,Rotifer,Protozoa.The main foods were Advanced plants(57.92%),Crustacean(16.18%)and Piscium(8.6%)of female crab before spawning,and the main foods were Advanced plants(45.96%)and algae(40.41%)for female crabs after spawning.However,the main foods were mainly algae and detritus by analysis of gastric contents of the female crabs before and after spawning.The percentages of algae were 43.33% and 66.82% respectively and the frequency of detritus reached 50%-80% of the female crabs before and after spawning.One of the reasons for the difference of two ways is that the food in the gastric was analyzed by the gastric content method,while the intestinal contents were analyzed by the high-throughput sequencing method.The algaes were easy to digest and absorb,most of the algae had been digested when the food residues reached the intestinal tract,resulting in the decrease of the proportion of algae in the high-throughput sequencing method.On the other hand,the reason was that the indistinguishable and detritusmay be formed by the digestion and decomposition of plants and animals in the gastric contents in the first chapter,which are identified in high-throughput sequencing method.Therefore,that increases of the proportion of food for plants and animals.Atthe same time,comparing with morphology,animal foods were identified by high-throughput method,such as Liza haematocheila,Acanthogobius ommaturus,Nassarius festivus,Exopalaemon annandalei,Daphnia,Lamellibranchia,Opepoda,and plant foods were identified such as Phragmites communis,Eichhornia crassipes,Scirpus mariqueter,Spartina alterniflora.3.Intestinal microbial diversity of female E.sinensis during migratory period in the Yangtze EstuaryThe intestinal microbial diversities were studied by 16 s V4 high-throughput sequencing technique of female crab before and after spawning in the Yangtze Estuary.The results showed that OUT were detected accounted for 313 and 376 respectively in the female crab before and after spawning,and the specific OUT accounted for35.78% and 46.54%,respectively.Tenericutes,Proteobacteria,Firmicutes and Bacteroidetes are the main flora of intestinal.There are differences in the microbial diversities of female crab before and after spawning(P<0.05).At the phylum level,Tenericutes and Platytomycetes in the female crab after spawning are larger than that of female crab before spawning.The reason for the high content of the Phytophthora in female crab after spawning is related to the fact that Phytophthora is a microorganism that maintains the healthy growth and development of the embryo.The relative content of Planctomycetes in the sediment is relatively high.Therefore,The reason for the high content of the Planctomycetes female crab after spawning is related to the spawning is buried in the sediment and the detritus in the food is relatively large.At the genus level,the Anaerorhabdus in the female crab before spawning were larger than the female crabs after spawning(P<0.05),while the Lactobacillus was smaller than the female crabs after spawning(P<0.05).Anaerorhabdus mostly exist in the intestinal tract of carnivorous organisms,while Lactobacillus mostly exists in the intestinal tract of herbivorous organisms.Gastric analysis and high-throughput sequencing studies have shown that: the proportion of animal foods for female crabs before spawning was larger than that for female crabs after spawning,while the proportion of algae and aquatic plants were smaller than that for female crabs after spawning,indicating that the difference in foods was one of the reasons for the difference in intestinal diversities for female crabs before and after spawning.At the same time,Vibrio and Aeromonas were detected in the female crabs before and after spawning in this study,these two kinds of bacteria are usually found in omnivorous animals.