Effects Of Peanut Skin Proanthocyanidins Supplemented In Diets Of Juvenile American Eel (Anguilla Rostrata) On Growth,Antioxidant Capacity And Lipid Metabolism

In recent years,there are more and more studies on grape seed proanthocyanidins as a functional feed additive to improve the growth and health status of many fish species,while no research on the application of other sources of proanthocyanidins is conducted in fish diet.In the present study,different levels of peanut skin proanthocyanidins(PSPc)were supplemented in the diet of American eels(Anguilla rostrata).The changes in parameters related to growth performance,body antioxidant capacity,intestinal flora,and lipid metabolism were used to evaluate the supplementation effect,which could provide the reference for the PSPc application in the eel diet and the development of a new source of proanthocyanidins.A total of 450 juvenile American eels with an average body weight of 10.50±0.03 g per fish were randomly divided into five treatment groups,and they were fed with basal diet(PSPc0 group),PSPc supplemented with 300 mg/kg(PSPc300 group),600 mg/kg(PSPc600 group),900 mg/kg(PSPc900 group)and 1200 mg/kg(PSPc1200 group),respectively.There were three replicates with 30 fish in each replicate in each treatment group.The trial period was 8 weeks.Results:Compared with PSPc0 group,the eels in PSPc supplementation groups had the higher values of final body weight,weight gain rate and specific growth rate,feed efficiency(except for PSPc300group),and feeding rate(except for PSPc600 and PSPc1200 group)(P<0.05),the eels in PSPc900 group had the best growth performance.The optimal levels of PSPc supplementation based on weight gain rate and feed efficiency in the diet of the eel are 922.17 mg/kg and 934.73 mg/kg,respectively.The juvenile American eels in PSPc supplementation groups had the lower crude lipid content of the whole fish(except for PSPc300 group)(P<0.05),the lowest lipid content was found in PSPc900 group.The eels in PSPc supplementation groups had higher activities of intestinal lipase and protease(P<0.05),the activities values of those enzymes were the highest in the PSPc900 group.The increased villus height and muscular thickness(except PSPc300 group)of the intestine were found in PSPc supplementation groups(P<0.05).Compared with PSPc0 group,the eels in PSPc supplementation groups had the higher levels of total antioxidant and reduced glutathione and the activities of superoxide dismutase,catalase,glutathione peroxidase,and glutathione S-transferase in serum,liver,and intestine(P<0.05),and the changes of these parameters showed a trend of firstly increased and then decreased with the increasing dietary PSPc supplementation level,the highest values of the above parameters were shown in eels of the PSPc900 group(except for glutathione S-transferase in intestine).The lower level of malondialdehyde was in the serum,liver,and intestine of the eels in PSPc groups(P<0.05).The change of malondialdehyde level showed a trend of firstly decreased and then increased with the increasing dietary PSPc supplementation level,the lowest level of malondialdehyde in serum and intestine was in eels of the PSPc900 group,the lowest level of malondialdehyde in liver was in eels of the PSPc600 group.The eels in PSPc supplementation groups had lower levels of hydrogen peroxide and nitric oxide and higher ability of anti-free radical superoxide anion and anti-free radical hydroxyl ability in the liver and intestine(P<0.05),the eels in PSPc900 group had the lowest levels of the free radicals.The diversity and richness of intestinal flora of eels in PSPc900 group were lower than those of PSPc0 group.At the phyla level,the relative abundances of Firmicutes,Proteobacteria,and Actinobacteria were increased in the intestine of eels in PSPc supplementation groups,while the relative abundances of Tenericutes and Fusobacteria were decreased.At the genus level,the relative abundances of Citrobacter,Chroococcidiopsis,Escherichia shigella,Cupriavidus,Pelomonas,and Romboutsia were higher in PSPc0 group(P<0.05),the relative abundance of Xanthomonadaceae was significantly higher in PSPc900 group(P<0.05).Compared with PSPc0 group,the eels in PSPc supplementation groups had the lower levels of serum triglyceride and low density lipoprotein cholesterol(P<0.05),only the eels in PSPc900 group had the lower levels of serum total cholesterol and higher levels of high density lipoprotein cholesterol(P<0.05).The eels in PSPc supplementation groups had lower levels of triglyceride and total cholesterol in the liver(P<0.05),and there were no significant differences of low density lipoprotein cholesterol and high density lipoprotein cholesterol in the liver among all treatments groups(P>0.05).The activities of lipoprotein lipase,hepatic lipase,and total lipase in the liver of eels in PSPc supplementation groups(except for PSPc300 group)were significantly increased(P<0.05),and the activities of fatty acid synthase and acetyl-Co A carboxylase in the liver were significantly decreased(P<0.05).Liver oil red O staining showed that the number of lipid droplets in PSPc0 group was less than those in all PSPc supplementation groups,almost no lipid droplets were found in the liver of eels in PSPc900 group.Compared with PSPc0 group,dietary 900 mg/kg PSPc supplementation up-regulated the levels of phosphatidylcholine and phosphatidylethanolamine and down-regulated the levels of ceramide and 2-lysophosphatidylcholine in the liver of juvenile American eel,and regulated lipid metabolism by affecting autophagy,sphingolipid metabolism,glycerophospholipid metabolism,and linoleic acid metabolism pathways.In conclusion,an appropriate level of PSPc supplemented in diet could promote growth by improving the activities of some intestinal digestive enzymes and morphology of intestine,positively regulating intestinal flora,improving the antioxidant capacity,reducing levels of serum lipid and liver lipid,regulating the activities of lipid metabolism enzymes,lowering the lipid accumulation of liver,and inhibiting lipid synthesis of the liver by affecting autophagy,sphingolipid metabolism,glycerophospholipid metabolism and linoleic acid metabolism pathways in liver of juvenile American eel.However,excessive supplementation of PSPc is detrimental to the growth,body antioxidant capacity and intestinal health of juvenile American eels.The recommended supplementation range of PSPc in the diet might be 922.17-934.73 mg/kg for the best growth performance of juvenile American eels.