Cetobacterium somerae as a microbial correlate of improved muscle quality after intestinal microbiota transplantation in Yellow River carp (Cyprinus carpio).

Dietary faba bean enhances fish muscle quality but concurrently reduces growth performance. The gut microbiota critically modulates muscle growth and quality. However, the specific microbial taxa, metabolites, and regulatory mechanisms responsible remain to be elucidated. This study established a differential gut microbiota model in faba-bean-fed Yellow River carp (Cyprinus carpio), used whole-intestinal microbiota transplantation (WIMT) to directly test its effect on muscle quality, and supplemented the key bacterium and its metabolite to confirm their contribution. After a 6-week faba bean diet, growth performance declined, whereas muscle texture improved (P < 0.05). This improvement was concomitant with a higher abundance of the genera Aeromonas and Cetobacterium in the gut. Following 8 weeks of daily WIMT from faba-bean-fed donors, Yellow River carp maintained normal growth performance (P > 0.05) and simultaneously showed improved muscle texture, characterized by more small-diameter fibers, lower fat content, and higher collagen levels (P < 0.05), recapitulating the donor's key muscle phenotype. Meanwhile, WIMT reshaped the gut microbiome composition and its metabolic profile, and the marker species Cetobacterium somerae and its metabolite acetic acid showed associations with improvements in muscle quality. Further in vivo validation indicated that C. somerae reduced fat deposition and improved muscle texture, an effect possibly linked to activation of the AMPK-PGC-1α-FoxO pathway, and its metabolite acetic acid mirrored these changes. This study reveals the direct impact of gut microbiota on muscle quality through WIMT in Yellow River carp, provides novel evidence of the fish gut-muscle axis, and offers a scientific basis for improving muscle quality.