Effects of dietary distiller's grains on growth and gut microbiota of the sea cucumber Apostichopus japonicus

This study evaluated the impacts of dietary distiller's grains (DG) on the growth, nutritional quality, and intestinal microbiota of Apostichopus japonicus . The healthy A. japonicus (21.51 ± 0.64 g initial weight) were allocated to four groups (three replicates each): a basal diet (T0) and three DG-supplemented diets: 10 % powder (T1), 20 % powder (T2), and 5 % liquid (T3), for 60 days trial. Growth parameters, nutrient profiles, and microbial communities were analyzed post-experiment. The group T3 exhibited significantly higher final body weight, weight gain rate, and specific growth rate versus controls ( P < 0.05), outperforming T1 and T2. Nutritional analysis revealed elevated crude protein in group T3 ( P < 0.05). Electron microscopy demonstrated denser collagen fiber bundles in group T3 compared to T1 and T2. Gut microbiota sequencing indicated distinct structural shifts in group T3, with increased Verrucomicrobia abundance (P < 0.05) and altered community similarity relative to controls ( P < 0.05). In comparison, T2 enhanced microbial alpha diversity ( P < 0.05), powdered DG (T1 and T2) impaired collagen synthesis and body wall quality despite promoting growth. In contrast, 5 % liquid DG supplementation (T3) optimized growth performance through protein enrichment and beneficial microbial modulation, particularly Verrucomicrobia proliferation. These findings demonstrate that liquid DG enhances A. japonicus aquaculture sustainability by improving growth metrics and nutritional value while modulating the gut microbial structure. • DG as a dietary ingredient improves growth and nutritional quality of A. japonicus . • 5 % liquid DG enhances growth and crude protein content in A . japonicus . • DG enhances collagen density, gut Verrucomicrobia and supports green aquaculture.