Abstract
This study aims to evaluate the effects of dietary emodin, high-dose vitamin C (Vc) and their combination on non-specific immunity and stress prevention of Wuchang bream, Megalobrama amblycephala Y., subjected to crowding stress. 1200 healthy fish with initial body weight of (133.442.11) g were selected and randomly divided into four groups: one was the control group fed with basal diet (containing Vc 50.3 mg/kg, with the L-ascorbyl-2-polyphosphate as Vc source), the three treated groups were fed with basal diets supplemented with emodin 60 mg /kg, Vc 700 mg/kg, and the combination of emodin 60 mg/kg + Vc 700 mg/kg, respectively. After feeding for 60 days, 25 fish per tank were exposed to crowding stress (100 g/L) for 48h, the biochemical parameters of blood and liver, liver two heat shock pro-tein 70s (HSP70s) mRNA levels, and cumulative mortalities of fish in each group were investigated at 0h, 12h, 24h and 48h, respectively. The results showed that, before crowding stress, compared with the control, serum total protein (TP), lysozyme (LSZ) and alkaline phosphatase (AKP) levels, liver superoxide dismutase (SOD) activity and expression level of inducible HSP70 mRNA increased significantly in emodin and Vc groups while serum cortisol (COR), triglyceride (TG) and liver malondialdehyde (MDA) contents decreased (P0.05); liver catalase (CAT) activity also significantly increased in emodin group (P0.05). Although serum TP, LSZ, and liver HSP70 mRNA levels significantly increased and liver MDA level decreased in combination group (P0.05), no synergism was observed. After crowding stress, compared with the control, the serum TP and AKP levels, liver SOD and CAT activities, and expression levels of HSC70 and HSP70 mRNAs increased in emodin and Vc groups in varying degrees and serum COR, glucose (GLU), glutamic-pyruvic transaminase (GPT), glutamic-oxaloacetic transaminase (GOT), TG and liver MDA levels decreased to some extent, whereas the LSZ activity decreased at first and then increased significantly (P0.05). Although these parameters had similar changing trend as above ones in combination group, it did not show any syner-gism either. Statistics showed that under crowding stress, the cumulative mortalities of emodin and Vc groups were sig-nificantly lower than that of control group at 24h and 48h (P0.05) while the difference between the combination and control groups was not significant (P 0.05). Therefore, the basal diet supplemented with emodin 60 mg/kg or Vc 700 mg/kg could improve non-specific immunity of fish, antioxidant capacity, and two HSP70s mRNA expression levels, and enhance resistance to crowding stress. However, the combination of emodin and high-dose Vc showed no better effect, the mechanism of their interaction needs further study.
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