Intestinal oxidative imbalance, inflammatory activation, and microbial dysbiosis are increasingly recognized as major factors affecting the health status of intensively cultured largemouth bass (Micropterus salmoides). Chlorogenic acid (CGA) is a plant-derived polyphenolic compound that is well known for its antioxidant and anti-inflammatory properties. Although its inclusion as a dietary supplement in aquafeeds has garnered increasing interest, its effects on intestinal health in largemouth bass under normal rearing conditions remain largely unknown. Hence, the present investigation was designed to elucidate how incrementally elevated dietary CGA concentrations modulate oxidative capacity, inflammatory gene expression, mucosal histological features, and enteric microbiota structure in juvenile largemouth bass. In this study, largemouth bass were fed diets containing 0, 200, 400, or 600 mg/kg CGA for 70 days, and we evaluated intestinal antioxidant capacity, inflammation-related transcriptional responses, histomorphology, and gut microbiota were assessed. The results demonstrated that CGA supplementation significantly raised intestinal total antioxidant capacity as well as the activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase, while substantially decreasing malondialdehyde levels (p < 0.05). The transcription levels of cat, gsh-px, gst, sod, nrf2, and ucp2 were markedly upregulated, whereas keap1 expression was downregulated (p < 0.05). CGA supplementation also reduced the transcription levels of several proinflammatory genes, including il-1β, il-6, il-8, tnf-α, nf-κb, p50, map3k, jak2, as well as stat3, while significantly elevating il-10 expression, in the 200 and 400 mg/kg groups, tgf-β expression was also lowered (p < 0.05). Histological examination revealed that CGA supplementation influenced intestinal morphology in a dose-dependent manner; the most consistent improvements in villus length, villus width, and muscularis thickness occurred at the 400 mg/kg level, whereas the 600 mg/kg level showed weaker effects in several parameters compared with the control. Furthermore, 16S rRNA sequencing indicated that CGA altered microbial diversity, community structure, and predicted functional profiles in the intestine. In summary, dietary CGA supplementation was associated with enhanced intestinal antioxidant capacity, modified inflammation-related transcriptional responses, changes in intestinal morphology, and shifts in the gut microbial community of largemouth bass. Within the tested dose range, the 400 mg/kg group exhibited relatively favorable responses in several measured indicators under the present experimental conditions.

This study investigated the effects of dietary Bacillus subtilis supplementation on growth performance, digestive enzyme activity, expression of antioxidant- and inflammation-related genes, and gut microbiota in juvenile GIFT (Oreochromis niloticus). The juvenile GIFT (total 540, initial body weight: 16.17 ± 1.32 g) were randomly divided into six groups and fed diets containing 0, 1 × 10⁷, 1 × 10⁸, 1 × 10⁹, 1 × 10¹⁰, or 1 × 10¹¹ CFU/kg B. subtilis for 60 days. Compared with the control group (0 CFU/kg B. subtilis), dietary B. subtilis significantly improved final body weight, weight gain rate, specific growth rate, and daily growth index and reduced feed conversion ratio (p < 0.05). Supplementation also significantly increased intestinal amylase, lipase, and trypsin activities (p < 0.05). In addition, the expression of several antioxidant-related genes was upregulated, whereas pro-inflammatory gene expression was generally downregulated in the intestine, liver, and head kidney. Gut microbiota analysis indicated that B. subtilis supplementation altered community composition, increased Firmicutes’ abundance, and reduced Proteobacteria abundance. Among all supplementation levels evaluated, the diet containing 1 × 10⁹ CFU/kg B. subtilis produced the most favorable overall beneficial effects under the conditions of the present study.