Water decoction of Astragalus membranaceus enhances cellular immune response and disease resistance in spotted maigre
The effect of dietary Chinese herb Astragalus membranaceus on the cellular immune response of spotted maigre (Nibea albifiora) was investigated. 300 spotted maigre with an average initial weight of 49.6 ± 5.5 g were selected and fed with different levels of water decoction of A. membranaceus (WDA) (0, 0.5, 1.0, 2.0 and 4.0%) for 4 weeks. Non-specific immune responses were measured after 0, 3, 7, 14, 21, 28 days of feeding. We then injected control and WDA treated fish with an intraperitoneal injection of Vibrio vulnificus, and recorded their mortality rate for 7 days post-infection. The results showed that the phagocytic index of phagocytes was significantly higher in 2% WDA treated group as compared to other groups (P<0.05). Whereas, the percentages of phagocytes were significantly higher in 0.5, 1.0 and 2.0% WDA groups as compared to 4.0% WDA and control groups (P<0.05). But lysozyme activities were significantly higher in the Astragalus-fed groups as compared to the control group (P≤0.05), and 2% group was the highest. Furthermore, 2% WDA-fed fish were significantly protected against V. vulnificus infestation (73.3% survival) as compared to 63.3, 53.3 and 36.7% survival in the 1 and 0.5% WDA-fed and control, respectively. In conclusion, dietary WDA may effectively enhance cellular immune response and disease resistance in spotted maigre against V. vulnificus.
Key words: Astragalus membranaceus, spotted maigre, non-specific immune response, Vibrio vulnificus.