The Nutritional And Physiological Adaptation Of Largemouth Bass To High Starch Feed

Carbohydrate is the cheapest energy material in feed,and its rational addition has been a key factor in the cost control of aquatic feed.The ability to use carbohydrates varies greatly depending on the species of fish,but in general,compared with mammals,the ability of carbohydrates in fish is low.The research object largemouth bass(Micropterus salmoides)belongs to the carnivorous fish whose carbohydrate utilization ability is very poor,in production practice,feeding the conventional commercial feed will cause it to appear in the middle breeding metabolic disorder,liver disease,and even death.This experiment is based on a practical feed formulation,with respectively 5%,20% of the dietary carbohydrate level,together with adjusted of the level of fat to make 2 kinds of diets with same level of nitrogen and energy,aims to explore the effect of dietary carbohydrate levels on the growth performance carbohydrate metabolism and antioxidant capacity of liver and serum biochemical indexes of largemouth bass,through the liver transcriptome analysis to investigate the mechanism of physiological response of largemouth bass on high starch feed from gene level.1.Effect of diet starch on growth performance,metabolism and antioxidant capacity of largemouth bassBased on a practical formula feed,set 5%?10% and 20%respectively of feed starch levels,together with a flexible feed fat level,to make 3 kinds of feeds with same nitrogen and energy level.Results show that diet starch levels significantly affected the growth performance of the largemouth bass.In the 4th and the 12 th week of the feeding experiment,the specific growth rate and protein efficiency of the 20% starch-level diet group were significantly lower than that in the 5% starch-level diet group(P<0.05),and the feed coefficient was on the opposite.In the 4th weeks,specific growth rate of largemouth bass in 10% starch-level diet group was significantly lower than that in 5% starch-level diet group(P<0.05),but at the 12 th week,it makes no significant difference(P>0.05),and significantly higher than the high carbohydrate group(P<0.05).The HSI of largemouth bass in 20% starch-level diet group was significantly higher than that it in the 5% starch-level diet group(P<0.05),and 20% starch-level diet group largemouth bass had a significantly higher liver,muscle glycogen content than 10% starch-level diet group and 5% starch-level diet group(P<0.05).The serum ALT and AST activity of 20% starch-level diet group were significantly higher than that in the 5% starch-level diet group(P<0.05),while the plasma TG level was significantly lower(P<0.05).The difference in ALP,TP,ALB,TC,GLU and insulin was not significant between the 5% starch-level diet group and the 20% starch-level diet group(P>0.05).GK,PFK and PK activity were significantly higher in 20% starch-level diet group(P<0.05),while the activity of PC and FBP was significantly lower(P<0.05).The level of dietary starch had no significant effect on the activity of HK,PEPCK and G6 Pase in largemouth bass(P>0.05).The activity of SOD and CAT was significantly lower in the liver and plasma of fishes in 20% starch-level diet group than that in the 5% starch-level diet group(P<0.05).There was no significant difference in the content of MDA in liver and plasma(P>0.05).Thus,largemouth bass can respond to feed carbohydrate levels adaptively by adjusting the activity of carbohydrate metabolic enzyme,to increase the carbohydrate storage in the body of the oxidation decomposition and conversion,but high level of feed carbohydrate makes liver damage to largemouth bass caused by excessive accumulation of hepatic glycogen,and make the oxidation resistance reduced,do harmful to the growth and health of the largemouth bass.2.Transcriptomics analysis of the liver of largemouth bass after feeding high carbohydrate diet.Feed the largemouth bass 12 weeks with diet starch level of 5%(low-starch group)and 25%(high-starch group)the do extraction to Largemouth Bass liver RNA,using Illumina Hi Seq for high throughput sequencing.Finally,we got 326651168 clean reads and 181691 Unigene,of which 81984 Unigene were successfully annotated in 7 public databases,accounting for 45.12% of total Unigene.The analysis found that the expression level of low-starch group and high-starch group of largemouth bass genes,7512 genes in total between different groups,high-cabohydrate group compared with the low-starch group,a total of 3038 up-regulated genes and 4474 downregulated genes.These genes were significantly enriched in these listed KEGG pathways: peroxisome proliferator activated receptor alpha signaling pathway,endoplasmic reticulum protein processing,peroxisomal fatty acid biosynthesis,signal transduction,biosynthesis of unsaturated fatty acids,starch and sucrose metabolism,is highly related to these pathways and growth and energy metabolism.The real time fluorescence quantitative PCR was used to verify the results,which proved that the results of RNA-seq were accurate and reliable.The data laid a good foundation for the further studies on the physiology adaptation mechanism to high carbohydrate feed of largemouth bass.