Dietary Scutellaria baicalensis extract enhances growth, intestinal health, and resistance to Aeromonas hydrophila in juvenile Asian swamp eel (Monopterus albus)

Abstract

Bacterial infection seriously restricts the healthy culture of Monopterus albus. Scutellaria baicalensis extract (SBE) is a natural plant‑derived additive with antioxidant and anti‑inflammatory properties. This study aimed to evaluate the effects of dietary SBE supplementation on growth performance, intestinal health, gut microbiota and resistance against Aeromonas hydrophila infection in juvenile Asian swamp eel. A 60‑day feeding trial was performed. Five diets were formulated with 0%, 0.5%, 1%, 2% and 3% SBE (CK, SBE‑A, SBE‑B, SBE‑C, SBE‑D). Growth indices, intestinal antioxidant status, intestinal histology, gut microbiota were detected. An A. hydrophila challenge test was carried out, followed by transcriptome analysis and qRT‑PCR verification of inflammation‑ and apoptosis‑related genes. Supplementation with 0.5% and 1% SBE significantly improved final body weight, weight gain rate and specific growth rate, and decreased feed conversion ratio. SBE increased intestinal GSH, SOD, T‑AOC and reduced MDA; antioxidant‑related genes ( CAT , GSH , SOD , Keap1 ) were markedly up‑regulated in the 1% SBE group. SBE optimized intestinal villus morphology, raised gut microbial diversity and the relative abundance of Cetobacterium , and decreased potential pathogens ( Plesiomonas , Brevinema ). After bacterial challenge, SBE improved survival rate, lowered tissue bacterial load and partially restored tight‑junction gene expression. Transcriptomics identified 5216 differentially expressed genes linked to inflammation, oxidative stress, metabolism and intestinal barrier. qRT‑PCR confirmed that dietary SBE regulated the expression of inflammatory and apoptotic genes induced by infection. Under current conditions, 1% dietary SBE produced the optimal beneficial effects. In summary, dietary SBE could enhance growth performance, maintain intestinal homeostasis and improve resistance to A. hydrophila in juvenile M. albus . 1% is the recommended supplemental level in this trial.