The Physiological Response Of Largemouth Bass(Micropterus Salmoides)to Dietary Starch Levels

Largemouth bass?Micropterus salmoides?is a typical carnivorous freshwater economic fish with poor ability to utilize carbohydrates.In production practice,largemouth bass fed with commercial compound feeds may experience metabolic disturbances,liver disease,and even death in the middle and late stages of breeding.Carbohydrates,as an economical and abundant feed energy substance,are essential in commercial fish feed formulations.For this reason,this experiment aims to explore the adaptive response of largemouth bass to dietary starch level from the perspectives of body metabolism,liver health,and transcriptomics,with a view to providing a basis for the scientific formulation of largemouth bass feed formulas.The main results of this study are as follows:1.Effects of dietary starch level on plasma biochemistry,glucose and lipid metabolism and liver health of largemouth BassImported steam fish meal,soy protein isolate?sugar-free?,wheat protein as the main protein source,fish oil,soybean oil?3:5?as the main lipid source,and corn starch as the sugar source.The starch levels are 5%,10%,and 15%Three kinds of isonitrogenous?CP47%?and isolipidic?EE11%?diets were fed largemouth bass with an initial weight of 8.63±0.05g for 8 weeks.The results showed that the dietary starch level significantly affected the growth performance and feed utilization of the largemouth bass.With the increase of starch level,the terminal average weight?FBW?and specific growth rate?SGR?of largemouth bass decreased significantly,while the feed conversion ratio?FCR?increased significantly?P<0.05?.Plasma alanine aminotransferase?ALT?,aspartate aminotransferase?AST?activity,and glucose?Glu?,liver glycogen,and liver lipid content in the largemouth bass in the15%starch level group were significantly higher than those in the 5%starch level group.The plasma triglyceride?TG?and total cholesterol?TC?levels were significantly lower than those in the 5%starch level group?P<0.05?.At the same time,it was found that the relative expression level of liver glucokinase?gk?was highest in the 15%starch level group,and the relative expression level of phosphoenolpyruvate carboxykinase?pepck?was the lowest?P<0.05?,while fructose-1,6-diphosphatase?fbpase?and glucose-6-phosphatase?g6pase?expression did not differ between groups.In addition,the relative expression levels of liver hormone-sensitive lipase?hsl?,peroxisome proliferator-activated receptor??ppar??,and carnitine palmitoyl transferase 1??cpt1??mRNA in the5%starch level group were all higher than 15%Starch level?P<0.05?.In contrast,the relative expression levels of liver fatty acid synthase?fas?,acetyl-CoA carboxylase?acc?,peroxisome proliferator-activated receptor??ppar??,and interleukin-8?il-8?mRNA were The 5%starch level was the lowest?P<0.05?,while there was no difference between 10%and 15%starch levels?P>0.05?.In addition,liver superoxide dismutase?sod?,catalase?cat?,glutathione peroxidase?gsh-px?,and interleukin-10?il-10?The relative expression of genes was the lowest?P<0.05?.With the increase of starch level,Bax gene expression was significantly up-regulated,while B lymphoma-2?bcl-2?gene expression decreased?P<0.05?.It can be seen that largemouth bass can adapt to changes in exogenous starch levels by regulating the expression levels of carbohydrate metabolism enzymes and lipid metabolism enzymes in the body.Excessive feed starch level inhibits the expression of liver lipolytic enzymes and promotes fat synthase,thereby increasing the content of liver glycogen and liver fat,causing the liver of largemouth bass to undergo inflammatory reactions,cell death,and reduce liver antioxidant capacity.This has a negative impact on the growth and health of largemouth bass.2.Effects of formulated diet and fresh frozen Hypophthalmichthys molitrix on growth,body composition and plasma biochemistry of largemouth bassLargemouth bass?initial weight:8.58±0.15g?was fed with 15%starch level?starch group?compound feed and fresh frozen Hypophthalmichthys molitrix?frozen H.molitrix group?for 8 weeks.The results showed that the final average weight?FBW?,crude lipid of whole fish,plasma TG,TC,and albumin?ALB?in the starch group were significantly lower than those in the frozen H.molitrix group?P<0.05?.The alkaline phosphatase?ALP?activity,calcium?Ca?,Glu,liver glycogen,and liver lipid content were significantly higher than those in the frozen H.molitrix group?P<0.05?.There was no significant difference in water content,ash content,and muscle glycogen content in the whole experimental groups?P>0.05?.It can be seen that compared with frozen H.molitrix group,the addition of starch diet can affect the growth and body composition of largemouth bass,and starch levels induce liver glycogen and lipid deposition.3.Transcriptomic analysis of largemouth bass liver after formulated diet and fresh frozen Hypophthalmichthys molitrixAfter feeding largemouth bass?initial average weight:8.58±0.15g?with 15%starch level?starch group?and fresh frozen Hypophthalmichthys molitrix?frozen H.molitrix group?for 8 weeks,the liver RNA of largemouth bass from starch group and frozen Hypophthalmichthys molitrix group was extracted,and Illumina HiSeq ^TM 4000 was used for Throughput sequencing.In the end,a total of283783492 clean reads and 181691 Unigene were obtained.After analyzing the gene expression levels of largemouth bass in two treatment groups,it was found that a total of 15738 differential genes appeared between the two treatment groups.Compared with the frozen Hypophthalmichthys molitrix group,a total of 13409 genes were up-regulated and 2329 genes were down-regulated in the starch group.There are 17 KEGG pathways significantly enriched:Cytokine-cytokine receptor interaction,Phagosome,Cell adhesion molecules?CAMs?,Jak-STAT signaling,PPAR signaling pathway and apoptosis etc.These pathways are highly correlated with immunity,apoptosis and energy metabolism.Besides the Drug metabolism-cytochrome P450 pathway,the number of genes with up-regulated differential expression is greater than that with down-regulated differential expression.Compared with the frozen Hypophthalmichthys molitrix group,the expression of glycometabolism-related genes hk,pfk and pk was significantly up-regulated?P<0.05?,while the expression of g6pase and pepck was significantly down-regulated?P<0.05?.The expression levels of tgf-beta,il1-beta,il-8,ccl2,ccl4 and ccl20,which are different genes between some inflammatory factors and chemokines,were significantly up-regulated?P<0.05?.The expression of some apoptosis-related genes,caspase-3,caspase-8 and caspase-9,were significantly up-regulated in the liver of largemouth bass?P<0.05?.It can be seen that compared with fresh frozen Hypophthalmichthys molitrix,the starch level of diet will affect the glucose metabolism of largemouth bass and damage the liver health.The metabolic characteristics of largemouth bass on fresh frozen Hypophthalmichthys molitrix and starch diet were comparatively studied in order to explore the mechanism of low-starch utilization of largemouth bass.