Effect Of Dietary Ascorbic Acid Level On The Growth Performance,Antioxidant Status And Hepatic Lipometabolism Of Grass Carp,Ctenopharyngodon Idella

The study was conducted to investigate the effects of dietary ascorbic acid on growth performance,antioxidant status,andlipid metabolism of juvenile Ctenopharyngodon idella.The results would provide the scientific basis for the application of ascorbic acid of grass carp feed.The results summarized as follows:1.Effects of dietary ascorbic acid on growth performance,feeding capacity of juvenile Ctenopharyngodon idella.6 experimental diets with 0,36,108,144,324,612mg/kgascorbic acid each,just indicatde as C1,C2,C3,C4,C5,C6.Juvenile grass carp with an initial body weight of（3.39±0.03）g were feed with a 56-days experiment.The results indicated that there were no significant difference in the survival rate（SR）,and weight gain（WG）between experimental groups and control group（P>0.05）,but an obvious uptrend.The feed intake（FI）was markedly higher than group C1（P<0.05）.The optimum addition level of dietary ascorbic acid was 334 and307mg/kg base on the broken-line model.2.Effects of dietary ascorbic acid on antioxidant capacity,disease resistance of Aeromonashydrophila strain of juvenile grass carp.After 56-days feeding experiment finished,fish were injected with Aeromonas Hydrophilaby intraperitoneal injection for 14 days,and the infection concentration was 2.4×10⁵ CFU/ml.The results showed that the mortality of all the treatmentswere not uplifted after 72 hours injected.The mortality of all the treatmentswere markedly lower than those of fish fed on the control diet C1（P<0.05）.After the feeding experiment,serum SOD and GSH-Px activity were no significant difference in other treatments（P>0.05）.After infection,dietary ascorbic acid levels still had no effect on SOD activityof fish fed all the diets（P>0.05）,but there was asignificant upward trend of serum GSH-Px activity of fish（P<0.05）.Before infection,liver SOD activityof fish fed the group C4 was markedly higher than those of fish fed on the other diets（P<0.05）,while no differences were observed in the activity of liver GSH-Px between other treatments（P>0.05）.After infection,SOD and GSH-Px activitysignificantly increased with the increasing dietary ascorbic acid level（P<0.05）.The optimum addition level of dietary ascorbic acid was 155-254mg/kg base on the broken-line model.3.Effects of dietary ascorbic acid on meat quality and hepatic lipometabolism.After the feeding experiment finished,the meat quality was analyzed and the result showed that shear force of fish fed group C5 was significantly less than other groups（P<0.05）.The groups C3,C5,C6 were significantly lowerthan control group C1（P<0.05）.Dietary ascorbic acid levels had no effect on the muscle diameterof fish fed all the diets（P>0.05）.The fatty acid was analyzed as the same time and the result showed that,the content of MUFA,PUFA,n-3PUFA and n-6 PUFA in liver had a declined tendency and then rised with the rising ascorbic acid levels.The result of muscular fatty acid was completely opposite.Hepatic mRNA expression of hepatic lipometabolism was analyzed and the result showed that the expression of FAS（fatty acid synthetase）,ACC（acetyl-coa carboxylase）and PPAR-γ（peroxisome proliferator-activated receptor-γ）mRNA had a significantly dropped tendency（P<0.05）.Hepatic mRNA expression ofUCP1（uncoupling protein 1）and CPT1（carnitine palmitoyl transferase 1）had a rised tendency and then dropped a bit,but no significant differents among all the treatments with the rising ascorbic acid levels（P>0.05）.In conclusion,ascorbic acid addition could increase the food intake and meat quality in a certain degree and many positive effects such as enhancing antioxidant capacity,protecting liver and promoting hepatic lipometabolism.O n the basis of the ascorbic acid content of serum and liver,the optima of ascorbic acid level was310-330mg/kg.And on the basis of the antioxidant capacity of grass carp,the optima of ascorbic acid level was 155-254mg/kg.