| In recent years,China’s aquaculture industry has developed rapidly,and its aquaculture output ranks first in the world.However,with the promotion of supply side reform and the increasing attention to environment protection,consumers’requirements for fish quality and aquaculture tail water emissions are gradually increasing.High-energy diet,that is,high fat and high carbohydrate diet,has been used in aquaculture feed for its advantages of effective addition in feed,low price and obvious sparing effect on protein.Although it plays a positive role in cost saving,reducing N and P emissions,it also causes the burden of fat metabolism of cultured fish to a certain extent.Moreover,the effects of high fat and high carbohydrate diets on fish muscle quality are still unknow.Blunt snout bream（Megalobrama amblycephala）is the sixth largest freshwater fish in China.It is popular because of its delicious meat and strong disease resistance.In view of this,this experiment will explore the effects of high fat and high carbohydrate diets on muscle fiber development and fat metabolism of Megalobrama amblycephala,in order to provide suggestions for reducing and avoiding fat metabolism diseases and producing healthy fish products while using high energy feed in aquaculture.This experiment is divided into the following two aspects.Experiment 1 Effect of high energy diet on growth performance and muscle fiber development of blunt snout bream Megalobrama amblycephalaThis study was carried out to explore the effect of high energy diets（high lipid/carbohydrate diet）on muscle growth of blunt snout bream.In vivo,three experimental diets,a control diet（6%lipid and 28%carbohydrate,CD）,a high lipid diet（11%lipid and 28%carbohydrate,HLD）and a high carbohydrate diet（6%lipid and 40%carbohydrate,HCD）,were formulated.Megalobrama amblycephala（19.80±0.15g）with good health and similar size were randomly divided into 3 groups,6replicates in each group,20 in each replicate.After 12 weeks,the samples were collected and analyzed.The results showed that high energy diet had no effect on the growth performance of blunt snout bream（P>0.05）.The springiness,gumminess,chewiness and muscle fiber density were significantly up-regulated in the high energy diet groups than CD group（P<0.05）.HLD significantly increase the muscle fiber CSA and muscle fiber diameter in the white muscle,whereas the opposite was true in the HCD group（P<0.05）.The hardness were significantly elevated in the HCD group（P<0.05）.High energy diet significantly elevate the transcriptional levels of Myf5,Myog and Mrf4,and reduce the transcriptional levels of Myod,MSTNa and MSTNb（P<0.05）.From these results,we can see that high energy diets can promote the muscle fiber hyperplasia.The transcriptional levels of AMPKα1,AMPKα2 and SIRT1 were significantly elevated in the HLD group（P<0.05）.The protein expressions of AMPK,p-AMPK,SIRT1 and p-AMPK/AMPK in the HLD group were significantly higher than that of CD group and HCD group（P<0.05）.The CAMK and CAN protein levels were significantly increased in the HCD group（P<0.05）.In vitro,the isolated primary hepatocytes from blunt snout bream were coincubated with 0.4m M OA and 40 m M D-glucose respectively.The results clearly state that 0.4 m M OA significantly increased the transcriptional levels of AMPKα1,AMPKα2 and SIRT1,the protein level of AMPK,p-AMPK,p-AMPK/AMPK and SIRT1（P<0.05）.The protein expression of CAMK and CAN in hepatocytes treated with 40 m M D-glucose were significantly higher than that in the other two treatments（P<0.05）.In summary,High lipid and high carbohydrate diets promote muscle growth through AMPK/SIRT1pathway and Ca2+-dependent pathway,respectively.Experiment 2 Effect of high energy diet on fat deposition and secretion in liver of blunt snout bream Megalobrama amblycephalaThis study was aimed to investigate the effect of high energy diet on fat deposition and secretion in the liver of Megalobrama amblycephala.The fish were randomly divided into the control diet group（6%lipid and 28%carbohydrate,CD）,high lipid diet group（11%fat and 28%carbohydrate,HLD）,high carbohydrate diet group（6%lipid and 40%carbohydrate,HCD）.After 12 weeks,the samples were collected for the determination of liver histology and molecular indicators.The results showed that the high enrgy diet had no significant effect on the growth performance of Megalobrama amblycephala（P>0.05）.The IPF of fish in the HLD group was significantly higher than that of CD group and HCD group.The HSI of fish in the HCD group was higher than that of CD group and HLD group（P<0.05）.The VLDL content in the serum of fish in the HLD group was significantly lower than that in the CD group（P<0.05）.High energy diet caused a large amount of fat deposition in the liver of Megalobrama amblycephala.The results showed that the transcription levels of DGAT1,FATP and FABP were significantly increased in the high energy diet groups（P<0.05）.The transcription levels of Cide B,GRP78,IRE1,XBP1s and XBP1u in HLD group were significantly higher than those of other two groups（P<0.05）,but the relative gene expression level of MTTP and ADRP were significantly lower（P<0.05）.In conclusion,high energy diet caused excessive fat deposition in the liver;high lipid diet led to endoplasmic reticulum stress and the decrease of VLDL exocrine level,but the increase of Cide B transcription level led to the increase of TG carried by VLDL;although high carbohydrate diet caused excessive deposition in the liver,but endoplasmic reticulum stress did not occur. |
