Effects Of Vitamin C On The Growth And Health Of Juvenile Procambarus Clarkii

Procambarus clarkii,commonly known as crayfish,is one of the main aquatic varieties in China.Vitamin C(VC)also known as ascorbic acid,is an important nutrient and immunoregulatory substance for fish and shrimp,but there are few studies on its nutrition in the feed of P.clarkii.Therefore,this experiment studied the regulation effect of feed with different VC content on the growth,metabolism,and immune resistance of P.clarkii,and proposed an appropriate amount of VC in the feed to promote the growth and health of the crayfish,and explored the stability of different VC forms in feed and the differences in the growth and immune response of P.clarkii,so as to screen out reasonable formulations for feed.The main findings are as follows:1.Effect of dietary coated vitamin C on the growth and health of P.clarkiiSix experimental diets(control,VC3,VC6,VC9,VC12 and VC15)with different levels of coated vitamin C(0.00%,0.03%,0.06%,0.09%,0.12% and 0.15%,respectively)were fed to juvenile crayfish(average weight: 7 g)for 10 weeks.The highest values of final body weight,specific growth rate,and muscle rate all occurred in the VC12 group(P < 0.05).Broken-line regression analysis on specific growth rate indicated that the optimal dietary coated vitamin C requirement of P.clarkii was estimated to be a 265.67mg/kg diet.Compared with the control group,the hepatosomatic index of the VC6 to VC15 group was significantly increased and reached the highest in the VC9 group(P <0.05);the feed conversion ratio was significantly reduced and reached the lowest in the VC12 group(P < 0.05);The crude protein and crude fat content of crayfish body increased significantly(P < 0.05).These results indicated that the appropriate addition of coated vitamin C in the feed could promote the growth and nutrient metabolism of crayfish,and feeding performance.The histology of the crayfish hepatopancreas in the control group showed that the hepatopancreas tubules were compressed,and the shape and size of the epithelial cells were deformed,which made cell identification difficult.The shape of crayfish hepatopancreas epithelial cells supplemented with coated vitamin C was more uniform.These results indicated that dietary supplementation of VC could improve the histology of hepatopancreas of crayfish.Blood immune indicators showed that with the increase of coated vitamin C content,crayfish serum phenol oxidase,lysozyme,superoxide dismutase,nitric oxide synthase,acid phosphatase,anti-superoxide anion activities,and nitric oxide content were significantly increased(P < 0.05);Crayfish total hemocyte count and blood cell respiratory burst activity were also significantly improved(P < 0.05).Hepatopancreas antioxidant capacity indicators showed that adding different coated vitamin C levels in feed could significantly increase the catalase and glutathione peroxidase activities and glutathione content(P < 0.05);Malondialdehyde content decreased significantly with the increase of coated vitamin C level(P < 0.05).These results indicated that supplementing the appropriate amount of VC in the feed could improve the non-specific immunity and antioxidant capacity of crayfish.2.Effect of P.clarkii fed with different vitamin C levels on the disease resistance of the white spot syndrome virus.A five-day challenge experiment was conducted on crayfish after the growth experiment of coated vitamin C.The results showed that the cumulative mortality of crayfish supplemented with VC was significantly lower than that in the control group(P <0.05).This showed that dietary VC could enhance the disease resistance of crayfish.3.Effect of dietary L-ascorbyl-2-monophosphate on the growth and health of P.clarkii.Six experimental diets(AMP0,AMP15,AMP30,AMP45,AMP60 and AMP75)with different levels of L-ascorbyl-2-monophosphate(0.00%,0.015%,0.03%,0.045%,0.06%and 0.075%,respectively)were fed to juvenile crayfish(average weight: 0.7 g)for 10 weeks.The results showed that compared with coated vitamin C,L-ascorbyl-2-monophosphate in the diet also improved the growth and feeding performance of crayfish.Broken-line regression analysis on specific growth rate indicated that the optimal dietary L-ascorbyl-2-monophosphate requirement of P.clarkii was estimated to be 300.95 mg/kg diet;the crude protein content of crayfish body increased significantly(P < 0.05).These results indicated that P.clarkii had a higher requirement for dietary L-ascorbyl-2-monophosphate,and the addition of L-ascorbyl-2-monophosphate to the diet also promoted the nutritional reserve of P.clarkii.After adding a suitable L-ascorbyl-2-monophosphate,part of the blood immune parameters significantly enhanced(P < 0.05).This result indicated that dietary L-ascorbyl-2-monophosphate could also improve the immunity of crayfish.By comparing the retention rate of the two forms after feed processing,the retention rate of L-ascorbyl-2-monophosphate in this test feed is higher.This study can provide a theoretical basis and reference data for the preparation and health adjustment of crayfish’s feed,so as to promote the growth of crayfish and reduce the occurrence of diseases and deaths of cultured crayfish.