A Novel Indigenous Probiotic, Clostridium moniliforme G18, Confers Health Benefits to Mud Crabs (Scylla paramamosain).

Butyrate-producing bacteria (BPB) are widely used as additives in aquaculture because of the beneficial effects of the butyrate they produce. However, most available BPB currently are of terrestrial origin, which are quite different from aquatic animals, resulting in profoundly unstable probiotic performance. This study isolated a novel, indigenous BPB, Clostridium moniliforme G18, from the gut of mud crabs, Scylla paramamosain. The strain demonstrated robust butyric acid production, tolerance to gastrointestinal conditions (pH 4-9, 0-3% NaCl, 0.4-1.0% bile salts), antibiotic sensitivity, pathogen inhibition, and non-hemolytic activity. Dietary supplementation with G18 alone or in combination with resistant starch and galactooligosaccharides (GR18) significantly enhanced mud crab body weight (P < 0.05). The supplementation improved intestinal health by enhancing histomorphology and upregulating tight junction genes (ZO-1 and Claudin). Furthermore, it boosted antioxidant capacity (elevated SOD and CAT; reduced MDA), modulated immune responses (increased AKP and ACP; reduced ALT and AST, P < 0.05), and increased intestinal butyrate levels. Analysis of the gut microbiota of mud crabs fed G18 alone or in combination with prebiotics revealed an increase in alpha diversity and beneficial composition changes (including reduced Vibrionaceae and elevated Proteocatella, P < 0.05). Following Vibrio parahaemolyticus challenge, mud crabs fed G18 and GR18 showed significantly higher survival rate (66.7% and 73.3%, respectively, P < 0.05) versus 53.3% in the control group. These diets mitigated intestinal damage, restored immune and antioxidant parameters, and enhanced the expression of barrier function genes. These results establish indigenous C. moniliforme G18 as a highly promising probiotic candidate for enhancing growth and health in mud crabs.