Effects Of Different Diets On Intestinal Tissue Structure,Digestive And Immune Enzymes Activities,Microbiota Of Common Carp(Cyprinus Carpio)

In order to explore the effects of different diets on intestinal health of common carp,270 carps were randomly divided into three groups.They were fed with earthworms(Animal diets,group A),earthworms + duckweed(Mixed diets,group M),duckweed(Plant diets,group P).The differences of intestinal tissue structure,digestive and immune enzyme activities,intestinal microbiota were analyzed in order to provide a theoretical basis for healthy breeding of common carp.1.intestinal tissue structureExcept of the midgut fold height,common carp of group A had better intestinal fold height,fold width and fold absorption area than other groups(P < 0.05),especially in the foregut.In addition,there was no difference in fold width and fold absorption area of common carp in group M and group P(P > 0.05),but the height of intestinal folds in group M was significantly higher than that in group P(P < 0.05).The intestinal mucous cells of common carp are mainly type II and type IV,especially type II mucous cells.In present study,the total number of mucous cells in group P was the largest,followed by the group M,and group A was the least.2.Intestinal digestive and immune enzymes activitiesThe results showed that activities of trypsin and lipase in group A was the highest,followed by group M,that in group P was the lowest.However,the activities ofα-amylase and cellulase were opposite to the activities of trypsin and lipase.Although the activities of immune enzymes showed different characteristics,in general,the contents of malondialdehyde(MDA)and nitric oxide(NO)in intestine of common carp in group M were lower,while the activities of lysozyme(LZM),acid phosphatase(ACP),alkaline phosphatase(AKP),total antioxidant capacity(T-AOC),superoxide dismutase(SOD),glutathione peroxidase(GSH-PX)and catalase(CAT)were higher.3.Intestinal microbiota analysisThe higher diversity and abundance of intestinal microbiota were observed in group M and group P(P < 0.05),but there was no significant difference between group M and group P(P > 0.05).Sequencing results showed that the dominant microbiota of the common carp intestine were the Proteobacteria,Bacteroidetes,Firmicutes and Fusobacteria.Common bacteria and unique bacteria were found in the intestinal tract of common carp in different feeding groups.The results of bacterial quantification showed that the total number of bacteria in group P was the highest,followed group M and finally by group A,significant differences among the three groups was measured(P < 0.05).In addition,the numbers of Firmicutes present in groups M and P were both significantly higher than those present in group A(P <0.05).Nevertheless,the number of Bacteroidetes in group P was significantly higher than group A and M(P < 0.05).In conclusion,the intestinal folds,the number of mucous cells,digestive enzymes and immune enzymes activities,microbiota of common carp were affected by the diets.These results indicate that common carp feeding on earthworms can improve their intestinal absorption capacity;the main parts of carp digesting and absorbing animal diets are concentrated in the foregut,while the digestion and absorption of plant diets are carried out in the whole intestine;mixed diets may be more conducive to the intestinal health of common carp;the dominant intestinal microbiota is conducive to the digestion of common carp.