The Growth Performance,Intestinal Microbe Composition And Feeding Habit Of Juvenile Chinese Mitten Crabs (Eriocheir Sinensis) Under Three Diet Feeding Modes

The diet feeding mode of the bait plays a crucial role in the growth and development of the juvenile Chinese mitten crab（Eriocheir sinensis）.In the early experiments of this research group,it was found that Alternanthera philoxeroides and formulated diet are the favorite bait for juvenile crabs.There is a lack of research results on the effects of these two foods on juvenile crabs in all aspects.Therefore,this study will compare the effects of different diet feeding modes on the growth,physiology and biochemistry,intestinal microbes,and food sources of juvenile crabs.At the same time,water peanuts will be added to the juvenile crab diet as a plant-feeding diet,with a view to improving Chinese mitten crabs.The promotion of formulated diet feeding mode for juvenile crabs and the development of formulated diet provide theoretical reference and practical basis.1.Effects of three diet feeding modes on growth performance of juvenile Chinese mitten crab（Eriocheir sinensis）The experiment took juvenile Chinese mitten crab as the research object,compared the growth performance,digestive enzymes,antioxidant enzymes and immune enzymes activities of E.sinensis in the Alternanthera philoxeroides（Diet1）,formulated diet（Diet2）and mixed treatment（Diet3）.Three replicates were set for each treatment with an experimental period of 120d.The results showed that,（1）At the end of culture,the terminal mass,weight gain rate,specific growth rate and hepatopancreatic index of juvenile E.sinensis in Diet 2 group were significantly higher than those in Diet1 and Diet3 groups.（2）Hepatopancreas and body crude fat content of juvenile E.sinensis in Diet2 and Diet3 groups were significantly higher than that in Diet1,while ash content showed an opposite trend.（3）Hepatopancreasα-amylase activity was the highest in Diet3（P<0.05）,while lipase activity was the highest in Diet2group（P<0.05）.（4）Serum catalase activity was the highest in the Diet1,while the total antioxidant capacity and malondialdehyde contents in the Diet2 and Diet3 groups were significantly higher than those in the Diet1 group.（5）Hepatopancreas serum catalase enzyme activity of juvenile E.sinensis was the highest in Diet1 group,superoxide dismutase activity and the total antioxidant capacity activity of female crabs in Diet2group were the highest（P<0.05）,and total antioxidant capacity activity of male crabs in Diet3 group was the highest（P<0.05）.（6）The activity of acid phosphatase and alkaline phosphatase in the serum of juvenile E.sinensis in Diet2 and Diet3 groups were significantly higher than that in Diet1 group,while in the hepatopancreas of male and female crabs,there was no significant difference in the activity of acid phosphatase and alkaline phosphatase among the three treatments（P>0.05）.Therefore,under the pond culture model of E.sinensis,feeding formulated diet based on reasonable planting of A.philoxeroides is beneficial to the growth,digestion and fat accumulation of juvenile E.sinensis,and enhances the antioxidant and immune capabilities of juvenile E.sinensis.This research could provide scientific reference and theoretical basis for the development of formulated diet for juvenile E.sinensis by adding A.philoxeroides as a plant-feeding diet.2.Effects of three diet feeding modes on the intestinal microbe composition of juvenile Chinese mitten crab（Eriocheir sinensis）The experiment took juvenile Chinese mitten crab as the research object,the experiment compared the intestinal microbe composition of E.sinensis in the Alternanthera philoxeroides（Diet1）,formulated diet（Diet2）and mixed treatment（Diet3）.Three replicates were set for each treatment with an experimental period of120d.The results showed that,（1）In juvenile crab intestinal contents and intima,the Simpson index was significantly different between Diet1,Diet2 and Diet3 groups（P<0.05）,while the Chao index in juvenile intestinal intestine was only between Diet1and Diet1.There were significant differences between the Diet3 groups（P<0.05）;in the Diet1,Diet2,and Diet3 groups,the inclusion and intimal Simpson index were only significantly different in the Diet1 and Diet3 groups（P<0.05）;（2）There was no significant difference in the three feeding modes of the intestinal contents and the bacterial groups in the inner membrane（P>0.05）.However,under the same feeding mode,the relative abundance of Firmicutes and Bacteroides in the intestinal lining of Diet1 was significantly higher than that of intestinal contents（P<0.05）.The relative abundance of the soft-walled bacteria in Diet2 intestinal contents was significantly higher than that in the intestinal lining（P<0.05）,while the Bacteroides phylum in the intestinal lining was significantly higher than the intestinal contents（P<0.05）,the relative abundance of the soft-walled bacteria in the intestinal lining of Diet3 is significantly higher than that in the intestinal lining,and the firm-walled phylum in the intestinal lining is significantly higher than the intestinal contents;（3）The 12 genera of intestinal contents and intima showed no significant difference among the three feeding modes（P>0.05）.The relative abundances of Mycoplasmataceae and Rhizobiales Incertae Sedis in the intestinal contents of Diet1 were significantly higher than those in the intestinal lining（P<0.05）,and the relative abundances of Roseimarinus and Dysgonomonas in the intestinal contents of Diet2 were significantly higher than those in the intestinal lining,Diet3 The relative abundance of intestinal contents Mycoplasmataceae was significantly higher than that of the intestinal lining（P<0.05）;（4）In different feeding methods,there are 382 genera in the intestinal content and 389genera in the intestinal lining,accounting for 51.4%and 42.1%of the total genera respectively.Candidatus Bacilloplasma and Mycoplasmataceae（12.73%）share the most common intestinal contents（>10%）,and Candidatus Bacilloplasma and Rhizobiales Incertae Sedis（18.11%）share the most common genera in the intestinal lining（>10%）;（5）In terms of different diet feeding modes,the intestinal contents and the common bacterial genera of the inner membrane under the Diet1,Diet2 and Diet3modes are 465,359 and 281,respectively,and account for 47.1%,42.5%and 41.9%of the total bacterial genera,respectively;（6）In terms of the composition of the bacterial community of the intestinal contents,Diet1 and Diet2 have the highest similarity,Diet2and Diet3 have the second highest similarity,and Diet1 and Diet3 have the lowest similarity.In terms of the composition of the bacterial community in the intestinal lining,Diet2 and Diet3 have the highest similarity,Diet1 and Diet3 have the second highest similarity,and Diet1 and Diet2 have the lowest similarity.However,for the same diet feeding mode,the intestinal contents of Diet1,Diet2 and Diet3 are relatively like the bacterial community composition of the intestinal lining.Therefore,under the pond culture model of Chinese mitten crab,feeding formulated diet based on reasonable planting of water peanuts is beneficial to the healthy growth of juvenile crabs.3.Study on the feeding habit of juvenile Chinese mitten crab（Eriocheir sinensis）under three diet feeding modesThe experiment took juvenile Chinese mitten crab as the research object,the experiment compared the feeding hab of E.sinensis in the Alternanthera philoxeroides（Diet1）,formulated diet（Diet2）and mixed treatment（Diet3）.Three replicates were set for each treatment with an experimental period of 120d.The results showed that,（1）In the stomach contents of juvenile crabs,the Shannon index was significantly higher than that of Diet2 in Diet1 and Diet3（P<0.05）.Chao index was significantly lowest in Diet2（P<0.05）;（2）The relative abundance ranking of the 7 most important phyla is:Chloroplastida>SAR>Arthropoda>Cryptomycota>Phragmoplastophyta>Rotifera>Unnamed Eukaryota（Eukaryota）,among which the SAR gate in the stomach content of Diet2 juvenile crabs is significantly higher than that in Diet1 and Diet3,and the Phragmoplastophyta in the stomach content of Diet1 juvenile crabs is significantly higher than that in Diet2 and Diet3,and Diet3 juvenile crabs Rotifera in stomach content was significantly higher than Diet1 and Diet2;（3）Regarding the stable isotope of juvenile crab muscle,the value of Diet1δ¹³C‰was significantly the lowest（P<0.05）,while the value ofδ¹⁵N‰was not significantly different among the three groups.As far as the juvenile crab food source is concerned,theδ¹³C‰values of the diets in Diet1,Diet2 and Diet3 are significantly different among the three groups（P<0.05）,and theδ¹⁵N‰value is significantly highest in Diet3;（4）Under the Alternanthera philoxeroides diet feeding mode,the first food source of juvenile crabs is water peanut,with an average contribution rate of 28.91%.Under the formulated feeding mode,the first food source of juvenile crabs is formulated feed,with an average contribution rate of 33.35%.In mixed feeding mode,the first food source of juvenile crabs is POM.Further analysis of the specific food contribution of the mixed group showed that the contribution rates of water peanut,zooplankton,POM and formulated diet were 10.39%,8.22%,20.63%and 33.15%,respectively.Therefore,in the pond culture mode of Chinese mitten crab,POM is essential as an energy supplement for juvenile crabs.It is recommended that Alternanthera philoxeroides be fed with a diet of 10.39%as the source of juvenile crabs to benefit the growth of juvenile crabs.