| Chinese mitten crab(Eriocheir sinensis),also known as river crab.Chinese mitten crab is also an omnivorous crustacean,which is fond of aquatic organisms such as water grass and snail.Snails are very important in crab aquaculture.It can not only be used as "natural guard" to purify water,but also be used as diet for river crab.However,whether snails can meet the nutritional needs of Chinese mitten crab,and what are the advantages and disadvantages of snails in terms of growth and basic metabolism compared with formulated feed? In this paper,the juvenile Chinese mitten crab "River & Sea 21" were used as the experimental crab,and the individual crab breeding system " Dragon Palace" was used to culture crab.The differences in the growth and molting of river crabs under two diets(snail and formulated feed)at a whole cycle were analyzed.At the same time,non-targeted metabolism LC-MS technology and microbial diversity study were used to analyze and compare the metabolic and gut microbiome of river crab fed with two diets,in order to provide reference for green culture and artificial selection of Chinese mitten crab.The main research results are as follows:1.Effects on molting and growth of Chinese mitten crab fed with snails and formulated feedIn order to understand the effects of different diets on the molting and growth of Chinese mitten crab,an individual culture system was used in this experiment.The differences in survival rate,weight gain rate,molting interval and digestive enzyme activities of Chinese mitten crab were analyzed and compared at one whole cycle under two different diets(Group L: snails;Group S: formulated feed).The results showed that: the survival rate of group L and group S was 86.67% and 93.33%,respectively.The body weight gain rate of group S after molting was significantly higher than that of group L(P < 0.05).The weight gain rate of group S was concentrated in 55-65%,while that of group L was mostly concentrated in 45-55%,and the molting interval of group S was about 5 days shorter than group L(P < 0.05).The hepatopancreas index of crabs in group S was significantly higher than that of group L(P < 0.05),but the meat yield rate of group S was significantly lower than that of group L(P < 0.05).The condition factor of two groups was the lowest at the postmolt stage and the highest at the premolt stage,however,there was no significant difference in both groups(P > 0.05).The next molting of Chinese mitten crab would start when its condition factor reached 60%.The trypsin activity in group S was significantly higher than that in group L(P < 0.01),the α-amylase activity was significantly higher than that in group L(P < 0.05),and there was no significant difference in lipase activity(P > 0.05).The results indicated the crab fed with formulated diet can better meet the nutrient requirements than that fed with snail,and crabs fed with formulated feed grow better.2.Effects on metabolomics analysis of Chinese mitten crab fed with snails and formulated feedThe feeding of formulated feed has become the mainstream trend of river crab culture,and snail plays an important role in the growth and development of river crab.However,there are few studies on the physiological metabolism of river crab at present.Therefore,in this study,the metabolomic analysis was conducted on the river crab fed with two kinds of diet by liquid chromatography-mass spectrometry(LC-MS).The results showed that: A total of 362 metabolites were identified and the metabolites were mainly enriched in 33 KEGG pathways.The pathways were mainly concentrated in lipid and amino acid metabolism pathways.The PCA and PLS-DA analysis showed that there were significant differences between the two groups.187 differential metabolites were identified.Compared with group L,132 metabolites were upregulated and 55 metabolites were down-regulated in group S.The up-regulated metabolites in group S were mainly concentrated in purine metabolism,choline metabolism and glycerolipid metabolism pathways.The up-regulated metabolites in group L were mainly enriched in glycolysis/gluconeogenesis,choline metabolism,inverse nerve signal and glycerolipid metabolism,and the purine metabolites in group S were more abundant than that in group L.About 65% of the differential metabolites were Lipids,and the rest were carbohydrates,nucleic acids,peptides,vitamins and cofactors,and steroids.The contents of pantothenic acid、allocholic acid and carnosine in group S were significantly higher than those in group L,and the contents of glucose,L-carnitine and heptadecanoyl carnitine in group L were significantly higher than those in group S.The results suggested that different diets had an effect on the metabolism of Chinese mitten crab.Feeding snail would increase the metabolism of L-carnitine and might inhibit the body weight gain of crabs.Feeding formulated feed would increase LPCs and might be harmful for health.3.Effects on gut microbiome analysis Chinese mitten crab fed with snails and formulated feedIngestion,living environment,growth stage and health status of the organism all affect the structure of intestinal microorganism.In order to understand the effects of different diets on the gut microbiome composition of Chinese mitten crab,the differences in gut microbiome composition of Chinese mitten crab under two diets were analyzed in this chapter.The results showed that: The dominant bacteria in group L were Firmicutes,Bacteroidetes and Proteobacteria,and the dominant bacteria in the group S were Actinobacteria besides the above three.The Chao index of group S was higher than that of group L,but there was no significant difference(P > 0.05).The Shannon index was significantly higher than that of group L(P < 0.01).The results showed that there was no significant difference in bacterial richness between the two groups,but the bacterial diversity in the group S was significantly higher than that in the group L.The composition of gut microbiome was closely related to the weight gain rate of Chinese mitten crab and different diets had a great influence on the difference of gut microbiome of Chinese mitten crab,which further affected its molting and growth. |
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