Improving intestinal health benefits by supplementation with emodin in juvenile largemouth bass (Micropterus salmoides): Intestinal morphology, digestion, microbiota and antioxidant capacity

Our study investigated the effects of dietary emodin on intestinal morphology, digestive function, gut microbiota, and antioxidant capacity in juvenile largemouth bass. A total of 540 fish (45 ± 0.3 g) were randomly assigned to six dietary treatments (EM0, EM250, EM500, EM1000, EM2000, and EM4000), corresponding to emodin supplementation levels of 0, 250, 500, 1000, 2000, and 4000 mg / kg, respectively. After a two-month feeding trial, emodin supplementation at 500–2000 mg / kg significantly increased intestinal villus height (VH), villus width (VW), and goblet cell (GC) count compared with the EM0 group ( P < 0.05). In contrast, the 4000 mg / kg dose significantly reduced VH and GC counts ( P < 0.05). Activities of digestive enzymes, including amylase, alkaline phosphatase (AKP), creatine kinase (CK), gamma-glutamyl transpeptidase (GGT), lipase, and pepsin, were significantly enhanced in the EM1000 group ( P < 0.05). Furthermore, emodin supplementation improved the composition, diversity, and richness of the intestinal microbiota in a dose-dependent manner. Specifically, EM1000 decreased the relative abundance of potential pathogens ( Fusobacteriaceae and Vibrionaceae ) and increased the abundance of potential probiotics ( Rubrobacteriaceae and Lactobacillaceae ) ( P < 0.05). This group further showed enhanced intestinal antioxidant and anti-inflammatory capacity, characterized by the elevated expression of catalase ( CAT ), heme oxygenase-1 ( HO-1 ), superoxide dismutase ( SOD ), and nuclear factor erythroid 2-related factor 2 ( Nrf2 ), along with reduced expression of the pro-inflammatory cytokines interleukin-8 ( IL-8 ) and tumor necrosis factor-alpha ( TNF-α ) ( P < 0.05). In summary, dietary emodin at 1000 mg / kg optimally modulated the gut microbiota and improved intestinal digestion, histomorphology, and non-specific immunity in juvenile largemouth bass.