Effects of Rehmannia glutinosa on growth performance, immunological parameters and disease resistance to Aeromonas hydrophila in common carp (Cyprinus carpio L.)

To explore the feasibility of Rehmannia glutinosa (RG) as a fish-feed additive, the effects of RG on the growth performance and the immune function of common carp, Cyprinus carpio L. (C. carpio), were investigated. Dried Rehmannia root powder (DP), prepared Rehmannia root powder (PP), dried Rehmannia root extract (DE) and prepared Rehmannia root extract (PE) were incorporated into the basal diet that was used to feed common carp for 80 d. The 540 juvenile fish with an average weight 7.46 ± 1.06 g were randomly allocated into nine groups, which were each fed one of the following diets: the basal diet as the control (Con), a diet adding 2% DP (LDP), a diet adding 4% DP (HDP), a diet adding 2% PP (LPP), a diet adding 4% PP (HPP), a diet adding 0.5% DE (LDE), a diet adding 1% DE (HDE), a diet adding 0.5% PE (LPE) or a diet adding 1% PE (HPE). The results indicated that the growth performance significantly increased in the groups HDP, LPP, HPP and HDE, compared with the control (P < 0.05). The nonspecific immune parameters, such as the lysozyme and leukocyte phagocytic activity, were also improved in all groups that added RG. However, only the HPP group had a significantly higher lysozyme activity, and the groups of LPP, HPP and HDE showed significant differences in the leukocyte phagocytic activity, compared with the control. With respect to immune-related genes, such as IL-1β, TNF-α and iNOS, upregulation was observed in the three measured organs-the head kidney, spleen and intestine-of fish fed with a diet supplemented with RG, compared with the control. In contrast, the gene expression of IL-10 or TGF-β was downregulated. Challenged with Aeromonas hydrophila (A. hydrophila), the survival rate was significantly higher in the groups HDP, LPP, HPP and HDE than in the control (P < 0.05). In this study, RG could promote the growth rate and strengthen the immune ability in common carp, which suggested that RG is a promising feed additive for C. carpio in aquaculture.