This study aimed to investigate the effects of dietary emodin, high-dose vitamin E
and their combination on the growth of Megalobrama amblycephala and its resistance
to acute crowding stress. The fish were randomly divided into four groups: a control
group fed with basal diet, and three treatment groups fed with basal diet supplemented
with 60 mg/kg emodin (the emodin group), 500 mg/kg vitamin E (the vit E group), and
60 mg/kg emodin together with 500 mg/kg vitamin E (the combination group). After 60
days, the fish were exposed to acute crowding stress for 24 h. The results showed
that the weight gain of the vit E group, specific growth rate of the vit E group,
total serum protein concentration (TP) of the vit E group, serum lysozyme activity
of the emodin group, serum superoxide dismutase (SOD) activity of the emodin group,
hepatic heat shock protein 70 (HSP70) levels of the vit E group and the emodin group,
and serum alanine aminotransferase (ALT) activity of the combination group significantly
increased while the weight gain and specific growth rate of the combination group
significantly decreased compared with the control group before stress. After crowding
stress, the vit E group had improved serum TP 12 h post-stress, hepatic SOD activity
24 h post-stress, and hepatic HSP70 mRNA levels 12 and 24 h post-stress while the
emodin group had enhanced serum SOD activity 12 and 24 h post-stress and hepatic HSP70
mRNA levels 12 and 24 h post-stress, as compared with the control. However, the serum
cortisol content of the three treatment groups 12 and 24 h post-stress, ALT activity
in the vit E group and emodin group 24 h post-stress, and serum alkaline phosphatase
and liver catalase activity in the combination group 24 h post-stress were lower than
those in the control group. The cumulative mortality was lower in the emodin, vit
E, and combination group after Aeromonas hydrophila infection compared with the control
group. Therefore, dietary supplementation with 60 mg/kg emodin or 500 mg/kg vitamin
E can improve HSP70 mRNA levels and antioxidant capabilities, resistance to crowding
stress, and growth in M. amblycephala. However, the combination of emodin and vit
E does not have a synergistic effect in M. amblycephala.