The study aims to evaluate the effects of dietary emodin,high-dose vitamin C(Vc)and their combination on growth,non-specific immunity and resistance to pathogens of Wuchang bream, Megalobrama amblycephala.1200 healthy fish with initial body weight(133.44±2.11)g were selected and randomly divided into four groups:one control and three tested.The control group was fed with basal diet(Vc content 50.3 mg/kg,with L-ascorbyl-2-ployphosphate as source).The three tested groups were fed with basal diets supplemented with 60 mg/kg emodin,700 mg/kg Vc,and 60 mg/kg emodin+Vc 700 mg/kg,respectively.Fish were fed twice daily(8:30 and 16:30)at a feeding rate of 2%-4% body weight.After 60 days feeding,the growth performance,muscle composition,biochemical parameters of serum and liver,the mRNA levels of two heat shock protein 70s(HSP70s),and survival rates after being infected with Aeromonas hydrophila were investigated.The results showed that compared with the control,the weight gain and specific growth rates,the levels of total protein(TP),lysozyme(LSZ)and the alkaline phosphatase(AKP)in serum,the activity of superoxide dismutase(SOD)and basal expression level of inducible HSP70 mRNA in liver were significantly improved(P<0.05),while feed coefficient,mortality,the contents of serum cortisol(COR)and triglycerides(TG),and liver malondialdehyde(MDA)were reduced(P<0.05)in emodin and Vc groups.Although the serum TP,LSZ levels,and the mRNA level of liver HSP70 increased significantly(P<0.05),and the liver MDA content also significantly decreased(P<0.05)in combination group,the synergism didn’t appear,and other indices were not significantly different(P>0.05)from the control.In addition,the liver catalase(CAT)activity was also significantly improved in emodin group compared with the control(P<0.05),while the CAT activities in Vc and combination groups were not significantly different from the control(P>0.05).Other indices,such as serum glucose(GLU),glutamicpyruvic transaminase(GPT),glutamicoxaloacetic transaminase(GOT),cholesterol(CHOL),the mRNA level of liver constitutive HSC70,the fish body indices,and muscle composition were not significantly different between groups(P>0.05).The challenge experiment with A.hydrophila showed that compared with the control the survival rates in emodin and Vc groups significantly increased(P<0.05)whereas the survival rate in combination group had no significant difference(P>0.05).These results indicate that the basal diets supplemented with emodin 60 mg/kg or Vc 700 mg/kg could promote the growth of fish,improve the nonspecific immunity,antioxidation capacity,and the basal expression level of HSP70 mRNA,and enhance disease resistance.However,the combination of emodin and highdose Vc showed no better effect,and the mechanism of their interaction remains to be further studied.