Effect Of Zinc On Functions Of Digestion, Immune And Antioxidative Of Juvenile Jian Carp (Cyprinus Carpio Var. Jian)

This study was designed to determine the dietary zinc requirement of juvenile Jian carp(cyprinus carpio var.Jian) by determining the effect of the graded levels of dietary zinc on growth performance,digestive ability and immune function.A total of 900 Jian carp(mean initial weight 15.71±0.01g) were randomly distributed into six groups of each three replicates,feeding diets containing graded levels of zinc(15.30,26.89,40.78,58.21, 68.92 and 92.45 mg kg^-1 diet) for 6 weeks.After 6 weeks feeding,a challenge trial was couducted by injection of Aeromonas Hydrophila(AH) for 17 days.Results indicated that from 3 weeks Jian carp fed with the zinc-unsupplemented diet gradually exhibited anorexia and poor growth.Zinc has great significantly(P＜0.01) or significantly(P＜0.05) enhanced SGR,feed intake(FI),feed efficiency(FE),protein production value(PPV) and lipid production value(LPV).There were great significantly (P＜0.01) or significantly(P＜0.05) correlation between SGR and the graded levels of zinc, feed intake,feed conversion efficiency,PPV and LPV(r₁=+0.999,P＜0.05;r₂=+0.970, P＜0.01;r₃=+0.935,P＜0.01;r₄=+0.968,P＜0.01;r₅=+0.960,P＜0.01),and there were great significantly(P＜0.01) correlation between FE and PPV or LPV(r₁=+0.898,P＜0.05; r₂=+0.898,P＜0.05).The path-analysis results indicated that feed intake and FE had great significantly direct effect on PWG(P_0.2=0.8056,d_0.2=0.6490,P＜0.01;P_0.3=0.1673, d_0.3=0.0280,P＜0.01),this suggest that dietary zinc may enhance feed intake and protein production to promote growth of juvenile Jian carp.Hepatopancreas weight,intestine weight and intestine length,the protein contents of hepatopancreas and intestine,trypsin, chymotrypsin,amylase,lipase activities in intestine and hepatopancreas,AKP,Na⁺, K⁺-ATP,CK,γ-GT activities in intestine were great significantly(P＜0.01) or significantly (P＜0.05) increased with the increase of dietary inositol levels.There were great significantly(P＜0.01) or significantly(P＜0.05) correlation between PPV and intestine weight,trypsin,chymotrypsin,protein content of hepatopancreas and of intestine (r₁=+0.968,P＜0.01;r₂=+0.927,P＜0.01;r₃=+0.990,P＜0.01;r₄=+0.915,P＜0.05;r₅=+0.879, P＜0.05;r₆=+0.845,P＜0.05;r₇=+0.894,P＜0.05),and there were significant(P＜0.05) correlation between FE and Na⁺,K⁺-ATP,AKP,γ-GT in proximal intestine(PIS),mid intestine(MIS) and distal intestine(DIS),and CK in whole intestine(r₁=+0.846,P＜0.05; r₂=+0.853,P＜0.05;r₃=+0.929,P＜0.01;r₄=+0.960,P＜0.01;r₅=+0.968,P＜0.01;r₆=+0.823, P＜0.05;r₇=+0.859,P＜0.05;r₈=+0.891,P＜0.05;r₉=+0.912,P＜0.05;r₁₀=+0.868,P＜0.05). Those suggest that dietary zinc promote growth of digestive and absorptive organ,enhance the ability of secrete digestive enzymes,improve activities of digestive enzymes and brush border enzymes,and enhance the ability of digestion and absorption of nutrient. Aeromonas hydrophila(AH) in whole intestine great significantly decreased in response to the increasing levels of dietary zinc(P＜0.01).Lactobacillus(LB) great significantly increased with zinc levels(P＜0.01).The hago-rate of leukocyte,survival rate after vaccination,total iron-binding capacity(TIBC),ACP activity,lysozyme activity,the level of lectine,and the contents of complement C3,complement C4 and immunoglobulin M (IgM) were great significantly increased with the increase of dietary zinc levels(P＜0.01). There were great significantly(P＜0.01) or significantly(P＜0.05) correlation between hago-rate of leukocyte and the head kidney weight,white cell population,red cell population,C3,C4,IgM,lysozyme and ACP activity(r₁=+0.938,P＜0.01;r₂=+0.909, P＜0.05;r₃=+0.877,P＜0.05;r₄=+0.975,P＜0.01;r₅=+0.974,P＜0.01;r₆=+0.884,P＜0.05; r₇=+0.878,P＜0.05;r₈=+0.934,P＜0.01).Those results indicated that zinc promoted immune function.Zinc significantly(P＜0.05) decreased malondialdehyde(MDA) and protine carbonyl in serum,intestine,hepatosomatic and muscle tissue.Zinc significantly (P＜0.05) increased superoxide dismutase(SOD),catalase(CAT),glutathione peroxidase (GSH-Px),glutathione S-transferase(GST),glutathione reductase(GR),anti-superoxide anion(ASA) and anti-hydroxy radical(AHR) activities in serum,intestine,hepatosomatic and muscle tissue.MDA in serum was negative related to AHR and GST in serum(r₁= -0.824,P＜0.01;r₂= -0.854,P＜0.05).And the correlation-analysis results indicated that there were great significantly(P＜0.01) or significantly(P＜0.05) negative correlation between MDA with the activities of SOD,CAT,GSH-Px,GST and GR in intestine(r₁= -0.970,P＜0.01;r₂= -0.851,P＜0.05;r₃= -0.983,P＜0.01;r₄= -0.916,P＜0.01).The effect of zinc on the activites of antioxidative enzymes in hepatosomatic and muscle have similar pattem with intestine.These results indicated that zinc may enhance the activites of SOD, CAT,GSH-Px,GST and GR,thus increased antioxidative defense systemes in fish.In summary,dietary zinc promote growth of digestive and absorptive organ,enhance the ability of secrete digestive enzymes,improve activitie digestive enzymes and brush border enzymes,and enhance the ability of digestion and absorption of nutrient;promote growth of juvenile Jian carp;dietary zinc improve phago-rate of leukocyte,lysozyme activity,C3,C4 and serum lectin to enhance the ability of recognization,chemotaxis, adherence,regulation,sterilization and bacteriostasis,and also improve antibody titer and IgM concentrations to enhance the ability of daptive immunity;dietary zinc promoted fish antioxidant capacity by removing superoxide anion and lipid peroxidative product.For 15-42g juvenile Jian carp appeared best growth performance as feeding the diets containing 48.69 mg zinc kg^-1 diet.Jian carp appeared best trypsin activity in intestine, AKP activity in proximal intestine,phago-rate of leukocyte,lysozyme activity and MDA in serum as feeding the diets containing inositol level of 43.10,69.29,41.47,44.60 and 60.86 mg kg^-1 diet,respectively.