Analysis Of Difference In Morphological Structure And Enzyme Activity On Different Parts Of Black Carp Intestine

Black carp is one of the four major fishes in freshwater aquaculture in China,and it is also an important species in aquaculture.With the development of intensive cultivation,the environment and health of farmed black carp have attracted more and more attention.Meanwhile,intestinal health and function are closely related to its growth and development.Therefore,in this study,we used the histological semi-quantitative system to evaluate the health status of farmed black carp,and used RNA-seq sequencing technology,histology and enzyme activity detection methods to investigate differentiate the digestive absorption and immune mechanisms of black carp foregut and hindgut.The specific research results are as follows:1.Histological indicators of farmed Black carp health statusHealth of fish in aquaculture is of increasing concern.In this study,we used the semi-quantitative histological system to evaluate the health status of Black carp raised under intensive aquaculture conditions.Gills,liver,kidney and intestine were fixed and dehydrated,and tissue sections were made using standard techniques.According to the scoring scheme proposed by Zimmerli et al.,the organ index of each tissue was calculated and used to classify the severity of histological change.The results showed that the gills,liver,and spleen of black carp were in good condition with class I and class II change.The intestine was the most affected organ with grade III changes.Intestinal histological analysis revealed intestinal mucosal epithelial cell hyperplasia and lamina propria friable and necrotic.Fulton's Conditional factor(CF)of the black carp ranged from 1.45 to 2.94,with an average value of 1.52;Hepatic somatic index(HSI)ranged from 0.29 to 0.93,with an average of 0.58,which indicated that the detected fish were in good condition.2.Study on the difference of tissue structure and distribution of digestive enzyme and antioxidant enzyme in different intestinal segments of black carpWe analyzed the difference of tissue structure and the distribution of digestive enzymes and antioxidant capacity in different intestinal segments of black carp by histological and enzyme activity detection methods.The results showed that the height of intestinal villi,mucosal thickness,muscular layer thickness and longitudinal section area of intestinal villi in black carp foregut were significantly higher than those in hindgut(p<0.05).However,the crypt depth and the number of goblet cells in black carp foregut were significantly lower than those in hindgut(p<0.05).At the same time,there are also significant differences in digestive enzymes and antioxidant capacity in the foregut and hindgut of black carp.The activity of amylase,lipase and trypsin in foregut is significantly higher than hindgut(P < 0.05).Different from the distribution of digestive enzyme activity,the activity of superoxide dismutase(SOD),slutathione reductase(GR),catalase(CAT)and the content of total antioxidant capacity(T-AOC)in the hindgut were significantly higher than that foregut(P < 0.05).The results indicate that the foregut of black carp may be the main part of its digestion and absorption of nutrients,and the hindgut plays a key role in resisting oxidative damage,anti-stress and protecting intestinal health.3.Transcriptome analysis of differentially expressed genes in foregut and hindgut of black carp.Fish intestines act for nutrient absorption,and also play an important role in immune barrier to inflammation and pathogen infection.This functional diversity is distributed in different segments of intestine.To explore the molecular mechanisms of functional varieties for the intestine,the transcriptomes of black carp foregut were compared to the hindgut.From the RNA of three foregut libraries and three hindgut libraries,we obtained 329.38 million raw reads,48.19 Gb clean bases,and 48,061 unigenes.We identified 1761 differentially expressed genes(DEGs)in the foregut and the hindgut.Of all DEGs,861 were significantly up regulated and 950 were significantly down regulated in the foregut as compared to the hindgut.Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)analysis indicated that the DEGs were primarily enriched in foregut for lipid metabolism,and hindgut for immune system.The transcriptome profiles of foregut and hindgut mass provide insights to the molecular basis underlying the functional specialization of intestine.