Feasibility Study On The Use Of Vallisneria Natans As Feed Material For Grass Carp,Ctenopharyngodon Idellus

1.Effects of adding Vallisneria natans meal to diet on growth performance,physiological and biochemical properties of juvenile grass carp(Ctenopharyngodon idellus)In this study,the effect of Vallisneria natans meal used as feed ingredient in the diet of grass carp(Ctenopharyngodon idellus)on growth,physiological and biochemical properties was evaluated.Four isonitrogenous and isoenergic diets were formulated by replacing the secondary powder and rice bran with 0(VN0,control),10%(VN1),20%(VN2)and 30%(VN3)V.natans meal.In addition,the group that fed fish only with fresh V.natans was designed.Juvenile grass carp of initial weight(18.85±0.20)g were selected to be cultured for 8 weeks in indoor cement tank cages.The results showed that the addition of V.natans meal did not affect the survival rate and feed coefficient of grass carp,the weight gain rate of VN3 group was significantly higher than VN2 group.With the increase of the amount of V.natans meal,the visceral index and hepatopancreas index decreased significantly,the activity of amylase in the foregut was significantly increased,and that in the middle and rear intestines was significantly decreased.The activity of amylase in the front,middle and rear intestines in the VN group was significantly higher than that in the other groups.In the control group,foregut,middle and rear intestines protease activity in turn strengthened,and with the increase of the content of V.natans meal the activity of foregut protease was significantly increased,and midgut proteinase activity increased first,then decreased and increased again,the highest value was observed in the group VN1,and the protease activity in the posterior intestine showed a significant decrease trend.The SOD activity of hepatopancreas was significantly increased,while MDA content decreased first and then increased,and that in the group VN3 was the highest.The content of serum totalprotein increased significantly,the serum albumin content increased first and then decreased,and the highest value was found in group VN1.Compared with the control group,serum ALT activity was increased and then recovered to the control level,and serum AST activity significantly decreased in V.natans meal groups,and there was no significant difference among the V.natans meal groups.The addition of V.natans meal resulted in significantly reduced apparent digestibility of the diets and enhanced resistance ability of grass carp to Aeromonas hydrophila to some extent.The group VN showed negative growth and depressed tvisceral index,hepatopancreas index,serum albumin,globulin and ALT;The activity of amylase in the intestinal segments was significantly higher than that in all practical formulated diets;The activity of midgut protease in VN group was significantly higher than that of control group,and that of hindgut protease was significantly lower than that of control group.The above results showed that the addition of 10% ~ 30% V.natans meal in the diet had no effect on the growth of grass carp,but was beneficial to the health of the fish body.It indicated that V.natans meal used as the raw material of grass carp feed for resource utilization would be much better than fresh V.natans.2.Effects of Vallisneria natans meal on muscle nutrient composition,collagen content and collagen gene expression of juvenile grass carpIn order to explore the effects of V.natans meal on muscle nutrient composition,collagen content and collagen gene expression of juvenile grass carp.Four isonitrogenous and isoenergic diets were formulated by replacing the secondary powder and rice bran with 0(VN0,control),10%(VN1),20%(VN2)and 30%(VN3)V.natans meal.In addition,the group that fed fish only with fresh V.natans was designed.Juvenile grass carp of initial weight(18.85 ±0.20)g were selected to be cultured for 8weeks in indoor cement tank cages.The results showed that: With the increase of the content of V.natans meal,the content of grass carp muscle crude protein increased significantly,while the content of crude fat and muscle collagen decreased significantly.The contents of various fatty acids in muscle were also significantly reduced,while the contents of n-3/n-6 were significantly increased.The total amino acid content of muscle was significantly increased,and the umami amino acid content of the V.natans meal groups was significantly higher than that of the control group.The relative expression levels of both collagen genes showed a trend of decline.The content of crude fat inmuscle of fresh V.natans group was significantly lower than that of other groups,the content of collagen was significantly higher than that of other groups,and the expression level of collagen gene was significantly lower than that of other groups,but n3/n6 was significantly higher than that of other groups,and the content of amino acid was significantly lower than that of other groups.The above results showed that the addition of V.natans meal within 30% in the feed could improve the muscle quality and nutritional value,and at the same time,the fish muscle of the V.natans addition groups might be beneficial to the health of human.The best results were obtained with 30%added V.natans meal.3.Effects of Vallisneria natans on intestinal flora of juvenile grass carpIn order to explore the effect of submerged plant bitter grass on intestinal flora of grass carps.In this study,16 S rRNA gene sequencing was performed on the intestinal tract contents of juvenile grass carps from the basic feed group(VN0),30% V.natans meal supplemental group(VN3)and fresh V.natans group(VN).The dominant phyla of grass carp intestinal was mainly Firmicutes,Proteobacteria and Actinobacteria.Community diversity and community abundance in the VN3 group were significantly higher than those in other groups,while those in the VN group were significantly lower than those in other groups(P < 0.05).At the phylum level,the relative abundance of Firmicutes and Gemmatimonadetes in VN3 group was significantly higher than that in VN0 group(P < 0.05)and the relative abundance of Firmicutes in VN group was also significantly higher than that in VN0 group(P < 0.05).At the genus level,the relative abundance of VN3 in Exiguobacterium and Bacillus was significantly higher than that in the VN0 group(P < 0.05).The relative abundance of VN group in Streptococcus and Erysipelatoclostridium was significantly higher than that in VN0 group(P < 0.05).The relative abundance of VN in the genera Exiguobacterium and Erysipelatoclostridium was significantly higher than that in the VN3 group(P < 0.05).The above results showed that different feeds could affect the structure of intestinal flora of grass carps,and the addition of V.natans meal could improve the diversity and abundance of intestinal flora of grass carps,promote the ability of the gut to disintegrate and utilize cellulose,and contribute to the health of fish.Feeding fresh V.natans not only reduced the diversity but abundance of intestinal flora,which was not conducive to intestinal health.4.Study on the metabolism for juvenile grass carp intestinal tract under different feed compositionIn this study,GC/MS non-targeted metabolomics was used to further explore the metabolomics of VN0(control group),VN3(30% V.natans group)and VN(fresh V.natans group)mentioned in chapter 1,and the obtained results were compared in two groups.The results showed that there were 114 different metabolites in group VN0 and VN3,including 21 amino acids,8 sugars and 7 nucleosides.There were 88 different metabolites in group VN0 and VN,including 14 amino acids,11 nucleosides,10 sugars and 4 fatty acids.There were a total of 58 different metabolites in group VN3 and VN,among which 7 were nucleosides,4 were sugars,4 were fatty acids,3 were organic acids,and 3 were energy metabolites.In addition,KEGG pathway mapper function analysis was used to show differences in metabolic pathways.V.natans have a significant effect on grass carp metabolic pathways,VN0 and VN3 group,and there was a total of 15 significant difference of path diagrams between VN0 and VN3 group,mainly containing ammonia acyl biosynthesis,valine,leucine and isoleucine biosynthesis,glycine,serine and threonine metabolism,purine metabolism,arginine and proline metabolism,valine,leucine and isoleucine degradation,tryptophan metabolism pathways.Between VN0 and VN group,there were 12 pathways with significant differences,including aminoacyl biosynthesis,aminoacyl biosynthesis,valine,glycine,serine and threonine metabolism,leucine and isoleucine,propionic acid metabolism,phenylalanine metabolism and other metabolic pathways.Compared VN3 group to VN group,there were 6 metabolic pathways with significant differences,mainly including purine metabolism,ascorbic acid and uronic acid metabolism,glutathione metabolism and galactose metabolism.The above results showed that different feeds had a great influence on the metabolites and the metabolic pathways enriched by different metabolites of grass carps.5.Effects of practical feed with fresh Vallisneria natans on growth performance,tissue biochemical indexes and muscle nutrients of juvenile grass carpOn the basis of the research in chapter 1 and chapter 2,in order to explore theeffects of different cultivation modes of V.natans on growth performance,tissue biochemical indexes,muscle nutrients and muscle collagen gene of juvenile grass carps.The basic feed(PA group)without V.natans meal was used as the control group,and the combination of the basic feed fed in the morning and fresh V.natans fed in the afternoon(PAB group)were acted as the experimental group.Grass carp with the initial average weight of 23.47 g were selected for the 8-week cultivation experiment in the indoor cement tank cage.The results showed that the weight gain rate and hepatopancreas index of grass carps in PAB group were lower than those in control group.The SOD,MDA and ALT levels of PAB in hepatopancreas were higher than those in PA group,and the levels of CAT and AST were lower than those in PA group.The total serum protein content in the PAB group was higher than that in the PA group,while other indexes were lower than those in the PA group.The content of crude protein and crude fat in muscle in the PAB group was lower than that in the control group.Total amino acids,non-essential amino acids and umami amino acids in PAB group were all higher than those in PA group.The total amount of saturated fatty acids,monounsaturated fatty acids,polyunsaturated fatty acids,and n-6 unsaturated fatty acids of PAB were all lower than those of the PA group,while the n-3/n-6 was higher than that of the PA group.There was no significant difference in collagen gene expression.The above results showed that grass carps grew rapidly when only fed with practical feed,but their muscle flavor and nutritional value were lower.When the practical feed and fresh V.natans were used alternately,the growth speed of grass carp was relatively slower,but the muscle quality was better,and the disease resistance of the fish might be stronger.