The Physiological Adaptation Mechanisms Of Micropterus Salmoides For High-lipid Diet

High-energy diets of good quality has become an important ensure for the sustainable development of ecological aquaculture at the present time.Not only can Highenergy diets have a growth promotion in fish,it also provides a protein-sparing effect.Appropriate amount of lipids in diets is able to hasten the growth of farmed fish;However,excessively high lipids in diet can easily trigger a supperabudant or abnormal fat depostion in fish,leading to metabolic disorders,growth inhibition and even death,which may increase risks of fish food.It remains unclear,at present,that how well and what the adaptation and adaptive mechanisms of fish to dietary lipids is.Consequently,it is a must that the adaptive machanisms of fish to high-lipid diets be thoroughly understood.Therefore,with Micropterus salmoides as the experimental object in our study,two isonitrogenous practical diets containing 1%(low-lipid group)and 7%(high-lipid group)crude lipid were fed to Micropterus salmoides,aiming to find out the effect of high-lipid diets on growth performance,lipid metabolism and liver antioxidant ability of Micropterus salmoides.1.Physiological adaptations of Micropterus salmoides triggered by high-lipid dietsThe results showed that the growth performance of Micropterus salmoides was significantly affected by the lipid levels.The final body weight,protein efficiency ratio and specific growth rate are significantly higher in high-lipid group than those in the lowlipid group(P<0.05).On the contrary,feed conversion rate and feed intake significantly lower in high-lipid group than in the low-lipid group(P<0.05).Two groups showed no significant differences in hepatosomatic index,viscera index and the lipid content in liver(P>0.05).The content of triglyceride,total cholesterol,high density lipoprotein cholesterol and low density lipoprotein cholesterol were significantly higher in high-lipid group than those in the low-lipid group(P<0.05),while no significant difference occurred in the Alanine aminotransaminase and Aspartate Aminotransferase of the two groups(P>0.05).Higher activity of catalase and content of malonaldehyde were observed in high-lipid group(P<0.05);while the activity of superoxide dismutase of two groups showed no significant change(P>0.05).The acetyl-Co A carboxylase,carnitine acyl transferase-? and adenosine monophosphate activated protein kinase showed higher activity in high-lipid group than those in the low-lipid group(P<0.05).Thus it can be seen that dietary lipids can be effectively utilized by Micropterus salmoides and promote its controling its food intake.Moreover,Micropterus salmoides are able to ease the highlipid imapact by increasing lipid oxidation and strengthening lipid extrahepatic transport,avoiding excessive lipid deposition in liver.2.Transcriptome analysis of Micropterus salmoides liver in response to high-lipid dietTwo isonitrogenous practical diets containing 1%(low-lipid group)and 7%(highlipid group)crude lipid were fed to Micropterus salmoides for 8 weeks.Then the extraction of RNA for both groups was conducted,after which the RNA sequencing techniques(Illumina Hi Seq)were carried out.Finally,the process generated 187802442 clean reads and 137977 Unigenes.55259 Unigenes were annotated in the 7 public databases,which accounted for 40.04% of the whole Unigenes.After analysis of the differencially expressed genes between the two groups of Micropterus salmoides,highlipid group showed 371 differencially expressed genes,among which 155 such genes were up-regulated,with rest ones being down-regulated.These genes were significantly enriched in several KEGG pathways,which mainly belonged to the following physiological process: fatty acid metabolism,adipocytokine signaling pathway,peroxisome proliferator activated receptors signaling pathway and Neuroactive ligandreceptor interaction,most of which are highly correlated with lipid metabolism.Real-time PCR showed that the results of RNA-seq are accurate and reliable.The research data is a good foundation for the study of the physiological adaptation of Micropterus salmoides to high-lipid diet.