Effects Of Dietary Tributylate On Growth Performance,Antioxidant Activity And Immune Of Juvenile Blunt Snout Bream (Megalobrama Amblycephala)

Megalobrama amblycephala is an important freshwater economic fish in China.This study,Juvenile blunt snout bream was studied to investigate the effects of dietary tributyrin(TB)on growth performance,immunity,intestinal tract and liver health.In this experiment,a single factor experimental design was adopted,and six TB diets with different gradients of isonitrogenous,isolipid and isoenergy [0%(control),0.03%,0.06%,0.09%,0.12% and0.15%] were set according to the commercial formula of Megalobrama amblycephala.Healthy and consistent juvenile blunt snout bream(6.5 ± 0.01 g)were randomly divided into 6 treatment groups with 3 replicates per group and 20 juveniles per replicate,and they were randomly divided into indoor recirculating aquaculture barrels(250 L).The period of experimental culture was 8 weeks.The experimental results are as follows:1.Effects of different TB levels on growth performance,physical indexes and body composition of Megalobrama amblycephalaAdding TB in the diet had positive effects on final weight(FW),weight gain rate(WG),specific growth rate(SGR)and feed ratio(FCR).Compared with the control group,FW,WG and SGR increased with the increase of dietary TB supplemental level(P<0.05),reached the maximum value when the dietary TB supplemental level was 0.06%,and then showed a downward trend.Compared with the control group,the condition factor(CF),visceral body ratio(VSI)and survival rate(SR)of Megalobrama amblycephala were not significantly affected by different TB levels in the diets(P>0.05).At the same time,different levels of TB in the diet had no significant effects on moisture,crude protein,crude lipid and ash content of the whole body(P<0.05).2.Effects of Different TB Levels on antioxidant and resistance to pathogenic infection of Megalobrama amblycephalaDiets supplemented with different levels of TB significantly increased the activities of total superoxide dismutase(T-SOD),glutathione peroxidase(GPx)and catalase(CAT)antioxidant enzymes in plasma(P<0.05).In addition,the plasma levels of anti-inflammatory cytokines [interleukin 10(IL-10)and transforming growth factor-β(TGF-β)] were significantly increased,while the levels of malondialdehyde(MDA)and pro-inflammatory cytokines [tumor necrosis factor-α(TNF-α)] were decreased(P<0.05).Through improve the body’s antioxidant capacity,reduce the inflammatory response to improve the body’s immune capacity.In addition,dietary TB supplementation significantly increased the levels of immunoglobulin [immunoglobulin M(Ig M),immunoglobulin G(Ig G)],Complement 3(C3)and interferon-γ(IFN-γ)(P<0.05).Surprisingly,0.06%-0.12%TB supplementation significantly increased the content of interleukin 1β(IL-1β)(P<0.05).However,different levels of TB had no significant effects on plasma glutathione(GSH),heat stress protein 70(HSP70),interleukin 8(IL-8)and total superoxide dismutase(T-AOC)activity(P>0.05).The mechanism of the improvement of immune capacity may be that TB activates phosphoinositide 3-kinase/protein kinase B/nuclear factor erythroid 2-related factor 2(PI3K/Akt/Nrf2)signaling pathway,inhibits nuclear factor-kappa B(NF-κB)signaling pathway,and further regulates the m RNA levels of the key genes of antioxidant capacity and inflammatory response.The m RNA levels of Nrf2,copperzinc superoxide dismutase(Cu/Zn-SOD),heme oxygenase 1(HO-1),CAT,Akt,PI3 K,GPx,IL-10 and TGF-β were up-regulated,and the m RNA levels of NF-κB and TNF-α were down-regulated(P<0.05).Different levels of TB had no significant effects on HSP70,manganese superoxide dismutase(Mn-SOD)and IL-8 m RNA(P>0.05).Aeromonas hydrophila challenge test showed that the mortality of the experimental group was lower than that of the control group.3.Effects of different TB levels on hepatic and intestinal protection ability of Megalobrama amblycephalaHE staining of the intestinal tract and liver of Megalobrama amblycephala was conducted.In the control group,the end of intestinal villi was dissolved and necrotic.The intestinal villi widened in 0.03% and 0.15% TB supplemental groups.In the control group,there was a small amount of inflammatory cell infiltration in the liver,while in the experimental group,the liver cells were arranged neatly,with clear contour and normal hepatic sinuses.Conciusion: The above results indicated that TB could increase FW,WG and decrease FCR in the growth of blunt blunt snout bream.In terms of improving the body’s immunity,TB can improve the activity of antioxidant enzymes and weaken the inflammatory response.In addition,TB supplementation can activate PI3K/Akt/Nrf2 and inhibit NF-κB signaling pathway,regulate health status,and prevent hepatic and intestinal injury.From the perspective of comprehensive growth performance and immune performance,the recommended addition dose of TB in feed is 0.06%.