Study On Digestive Physiology And Muscle Nutritional Quality Of Grass Carp From Different Habitats

The grassfish has high dependence on habitats,and its survival and muscle nutrient quality is susceptible to various habitat factors.Grass carp muscle from four habitats,including river,lake,high-density cultured pond and low-density cultured reservoir as research objects in this study,to determine the three aspects including digestion physiology,muscle nutritional compositions and quality characteristic,then compare the difference of different habitats on the digestive physiology and nutritional quality of grass carp.The main findings are as follows:(1)The gut tissue morphology of grass carp from different habitats showed that,the mucosafold height of grass carp in the cultured habitat was more,arrange more tight,the number of goblet cells in intestinal tissue was less than that of grass carp in natural habitats,the hindgut intestinal tissue lamina propria was separated and mucosal interstitial atrophy was damaged in the high-density pond culture habitat,which was a threat to the intestinal health of grass carps.There were significant differences in the activities of protease in the intestines of grass carps from four different habitats,but there were no significant differences in the activities of amylase and lipase,the activity of digestive enzymes of grass carp in high-density culture pond was significantly higher than that in the other other three habitats.Microbial diversity of the foregut was higher in the cultured habitats than natural habitats,whereas the diversity of the hindgut microbial community had the opposite trend,the intestinal microorganism composition of grass carps from different habitats mainly consisted of four species,the composition of the intestinal microflora of grass carps in different habitats was different,and the proportion of the intestinal microflora of grass carps in different sections in the same habitat was different,habitat had an effect on the intestinal microbial composition and community characteristics of grass carp,the larger proportion of Shewanella in the foregut of grass carp in high-density pond culture habitat,which has potential risk of disease.(2)The muscle fat content of grass carps from two breeding habitats was significantly higher than that from two natural habitats by comparing the nutritional composition of grass carps in different habitats.The ash content of grass carp in high-density pond culture habitat was the highest,indicating that the content of minerals and trace elements in muscle was higher.The muscle of grass carps from four different habitats had 17 kinds of amino acids,and the content of glutamate was the highest,and the contents of various amino acids were different.The TEAA/TAA and TEAA/TNEAA in muscle of grass carp were higher and the protein quality was better in high-density pond culture habitat.The EAAI value of muscle of grass carps in two breeding habitats indicated that the amino acid composition was more reasonable.The musculature of grass carps in the two natural habitats had a large proportion of umami amino acids,and the musculature of grass carps had better umami.18 kinds of fatty acids were detected in muscle of grass carps in four habitats,and the contents of various fatty acids were significantly different.The contents of n-6series fatty acids in muscle of grass carps cultured in ponds with high density were significantly higher,while the contents of n-3 series fatty acids were lower,with lower nutritional value and worse flavor.(3)The muscle color of grass carps in different habitats was different.The muscle a* value of grass carps in the two breeding habitats was lower,while the muscle b* value was higher,and the flesh color of grass carps in the two natural habitats was more yellowish green.In comparison,the muscle color of grass carps in the two natural habitats was better.The muscle hardness of grass carp in the two natural habitats was higher,the drip loss and the water loss rate after cooking were lower,which indicated that the muscle was tighter and the water power was stronger.The content of bitter histidine in muscle free amino acids of grass carp in two breeding habitats was higher,while the content of sweet amino acids such as glycine and umami glutamic acid in muscle free amino acids of grass carp in two natural habitats was higher,and the grass carp growing in natural habitat tasted more delicious.The content of unpleasant smell compounds,such as hexanal,1-octene-3-alcohol and 2-methylnaphthalene was higher in muscle of grass carp in culture habitat,and the fishy flavor and earthy flavor were stronger.