A feeding experiment was conducted to investigate the effects of Rehmannia glutinosa (RG) on the bacterial, archaeal, and fungal community composition in the gut of common carp (Cyprinus carpio L.). Common carp were given a control diet and an RG-supplemented diet (basal diet plus 4% prepared Rehmannia root powder) over a period of 80 days. Our results indicated that the bacteria Fusobacteria, Proteobacteria, and Bacteroidetes; the archaea Crenarchaeota and Euryarchaeota; and the fungi Basidiomycota are the most abundant microbial taxa in the gut of common carp. Compared with the common carp fed a control diet, the common carp fed an RG-supplemented diet contained a higher content of Akkermansia sp., and a lower proportion of Aeromonas sp. These results indicate that the consumption of a diet containing RG can lead to the accumulation of more beneficial microorganisms while inhibiting the growth of potential pathogens. Moreover, Crenarchaeota, the methanogenic, and Basidiomycota were detected in this study, these populations may be of high physiological relevance in carp because they have been implicated in human health and disease. Our results suggest that an RG-supplemented diet changes the intestinal microbial composition of common carp, which could have positive effects on the immune response of carp.

To evaluate the functions of safflower on aquatic animal, the effects of dietary safflower supplementation on growth performance, immunity response, short-chain fatty acids, and intestinal microflora of common carp (Cyprinus carpio L.) were studied in the present study. Four isonitrogen and isolipid experimental diets were formulated by adding 0, 0.25%, 0.50%, and 1.00% safflower to the basal diet (CON, S-0.25%, S-0.50%, and S-1.00%, respectively). The results showed that safflower supplementation (S-0.50%) significantly improves the growth performance (FBW, WGR, SGR) compared with that of the CON group ( P < 0.05 ). Similarly, safflower also promoted the CAT and LZM activities in the midgut, yet the content of MDA in the S-0.50% group was reduced ( P < 0.05 ). The content of proinflammatory factors (IL-1β, IL-12) in serum underwent significant reduction ( P < 0.05 ); the level of anti-inflammatory factor IL-10 had an upward trend in the S-0.50% group. Moreover, the mRNA expression levels of the IL-10, TGF-β, NF-κB, and TLR-1 gene in the head kidney were remarkably upregulated ( P < 0.05 ) in safflower addition groups, while IL-6 and IL-1β were downregulated significantly in the S-1.00% group ( P < 0.05 ). After 96 hours of the A. hydrophila challenge test, the survival rate of common carp had been improved greatly with the safflower addition, which was most impressive in the S-1.00% group. Additionally, the levels of acetic acid and butyric acid in intestinal contents were significantly higher in the S-0.50% and S-1.00% groups than in the CON group ( P < 0.05 ). Dietary safflower increased the intestinal microbiota abundance of Fusobacteria at the phylum level. At the genus level, the abundance of beneficial bacteria (Lactobacillus and Bifidobacterium) increased significantly in the S-1.00% group; some pathogens such as Aeromonas, Shigella, and Streptococcus were inhibited. Spearman coefficient analysis revealed that the contents of SCFAs were positively correlated with probiotics and negatively correlated with pathogens. In summary, safflower addition at an appropriate dose can promote the immune functions of the common carp by producing the short-chain fatty acids and regulating the intestinal microflora.

This study is aimed at exploring the effects of Bacillus coagulans NRS 609 on the growth performance, intestinal health, antioxidant activity, and immune response in common carp (Cyprinus carpio L.) by colonizing the intestinal tract with the beneficial strain. Gavage B. coagulans with GFP-tag at 109 CFU/mL into common carp for 7 days. Results indicated that B. coagulans were maintained in the intestine for at least 14 days. Four groups fed B. coagulans at different levels of inclusion, including 0 (CK), 1 × 10 7 (A), 1 × 10 8 (B), and 1 × 10 9 (C) CFU/g of feed for 8 weeks. Experimental groups showed significantly better growth performance than the control ( P < 0.05 ). The treatment groups had higher digestive enzyme activity, villus height, and muscle thickness than the control ( P < 0.05 ). Supplementation with B. coagulans also altered the composition of the intestinal flora. In addition, an enhancement of the antioxidant enzyme and a reduction of malondialdehyde in the liver were observed with the addition of B. coagulans ( P < 0.05 ). Moreover, the cytokines of IL-1β and IL-12, IL-10, and TGF-β, significant upregulation in experimental groups ( P < 0.05 ). Based on the results, the optimal level of B. coagulans was 107 CFU/g in diets for common carp.