Effect Of Different Lipid Source And Level On The Growth And Lipid Metabolism In Juvenile Grass Carp (Ctenopharyngodon Idellus)

Grass carp is the experimental animal,this study is divided into two parts.The first part studies the effects of different lipid source on growth,immunity,meat and lipid metabolism in grass carp;and the other part researches on the effect of high lipid level on growth,immune,and gene expression of lipid metabolism in the liver and muscle of grass carp.Experiment one: Palm oil(PO),rapeseed oil(RO),soybean oil(SO),linseed oil(LO)and fish oil(FO)as the lipid source,respectively,in diets of juvenile grass carp(Ctenopharyngodon idellus)(mean initial body weight,40.1 ± 0.3g)were to investigate the effect of dietary vegetable oil(VO)levels on growth performance,immune,meat quality and lipid deposition of liver and muscle.Each diet was randomly fed to triplicate groups in cages of the reservoir to apparent satiation for 8-week.Each cage range 35 tail fish.Experimental results show that different lipid source had no significant effect on the survival rate of grass carp(P>0.05).FO group had no significant effect with PO,RO,LO group in weight gain rate(P>0.05).The hepatosmatic index in FO group was significantly higher than other source of lipid groups(P<0.05).And condition factor of grass carp in RO,PO or LO groups all were significantly higher than FO and SO group(P<0.05).Dietary different lipid source have no significant influence on liver fat,whole fish protein,moisture and crude ash,but significantly affect the whole fish and muscle fat content.Grass carp’s crude fat in PO group was significantly higher than SO and RO group(P<0.05).FO group had a lower fat content in muscle than the other groups(P<0.05),and the LO group had the maximum value.The content of TC,TG and LDL in serum of the fish oil group were significantly higher than the other groups(P<0.05),and PO group had the maximum value of NEFA content in serum.There were highest muscle elasticity in FO group and PO group,and muscle adhesiveness and cohesion in FO group were significantly lower than the other groups(P<0.05),muscle chewiness and elasticity in linseed oil group were significantly higher than other groups(P<0.05).Compared with the FO group,the intestinal lipase,amylase and trypsin activity of grass carp in vegetable oil groups were significantly lower(P<0.05).ME activities of liver in RO and SO group was significantly higher than PO and LO group(P<0.05),but there was no significant difference between FO group and VO groups(P>0.05).Liver MDA content significantly increased in the PO group;and RO,PO and LO group showed a higher activities of LPL,HL,TL in liver,and significantly higher than FO and SO groups(P<0.05).The content of serum complement C4 in grass carp fed diets with FO is significantly higher than the VO groups(P<0.05),and GPT activity is significantly lower than the other groups(P<0.05).The activity of T-AOC in PO and LO group was significantly lower than other oil groups,LO group had a significantly higher GPT activity than other groups,and SOD activity was lowest in SO group.In brief,the different lipid source would affect the growth,muscle quality and health of grass carp,and under this experimental condition we could consider that RO may be the ideal vegetable oil source in grass carp diet.Experiment two: Soybean oil(SO)was as the lipid source,and set two kind of lipid level as 5%(normal level of lipid)and 15%(high level of lipid),respectively,in diets of juvenile grass carp(Ctenopharyngodon idellus)(mean initial body weight,113.7 ± 0.6g)were to investigate the effect of dietary oil levels on growth performance,immune,and the expression of lipid metabolism gene.Each diet was randomly fed to triplicate groups in cages of the reservoir to apparent satiation for 8-week.Each cage range 25 tail fish.Experimental results show that dietary high lipid level had no significant effect on survival ratio,condition factor,hepatosmatic index and organ-body ratios(P>0.05),but significantly increased the weight gain and specific growth ratio(P<0.05).The content of TG,TC in serum is not affected by high lipid level diet,but the serum GLU content was significantly increased(P < 0.05).The SOD activity is also have a trend to increase,however it had no significant difference with the control group(P>0.05);TP content and CAT activity were significantly decreased(P<0.05),among which TP content have significant difference with the control group(P<0.05).Gene expression of lipid synthesis genes,such as G6 PD,LXR,ICDH in liver in the high lipid group were significantly higher than the control group(P<0.05).Gene expression of SREBP1 in muscle was significantly decreased(P<0.05),and gene expression of FAS and LXR was on the decline,but no significant difference was found compare with the control group(P>0.05).Dietary high lipid significantly increased the gene expression of PPAR alpha,CPT1,LPL,HSL in liver(P<0.05),but have no significant impact on CPT1,LPL,HSL gene expression in muscle(P>0.05).On the contrary,PPAR alpha gene expression in muscle was significantly increased by dietary high lipid level(P<0.05).In brief,under the condition of this experiment,high lipid level has a promoting effect on grass carp growth,but it would affect the health of the grass carp.High lipid levels might promote the gene expression of lipid synthesis and lipolysis in liver,while it would reduce lipid synthesis in muscle in the cell to adapt to high intracellular lipid level.And there will have a synthesis regulation of FAS pathway as LXR-SREBP 1-FAS in liver and muscle.