Dietary effects of supplementing Clostridium butyricum culture or sodium butyrate in low fishmeal diet on growth, serum indicators, intestinal histology and microbiota of largemouth bass (Micropterus salmoides)

The present study aimed to evaluate the dietary effects of Clostridium butyricum culture (CC) or sodium butyrate (SB) on the growth, feed utilization, serum indicators, intestinal histology and microbiota of largemouth bass (Micropterus salmoides). CC and coated SB (50%) were supplemented to a low fish meal diet (245 g/kg) (control diet) at the inclusion levels of 1 g/kg and 2 g/kg, to form five iso-nitrogenous and iso-lipidic diets (control, CC-1, CC-2, SB-1, and SB-2). Then, the five diets were fed to largemouth bass with initial body weight of 70.2 ± 0.1 g. After 8 weeks of feeding, dietary supplementation of 1 g/kg CC increased the weight gain (WG) by 7.4% (P < 0.05), and decreased the feed conversion ratio by 0.09 (P < 0.05), while dietary SB just numerically improved the WG (P > 0.05), when compared to the control. The muscle composition was not significantly affected by the inclusion of CC or SB (P > 0.05). Dietary inclusion of CC or SB significantly reduced serum diamine oxidase activity and increased lysozyme activity (P < 0.05), while the decreased D-lactic acid level was observed only in the two SB groups (P < 0.05). In intestinal histology, the 1.0 g/kg CC group presented significantly higher intestinal villus height, width and muscle layer thickness than the control group (P < 0.05). The intestinal microbiota analysis showed that dietary CC or SB (1 g/kg) increased the abundance of Fusobacteriota and Cetobacterium, decreased the abundance of Proteobacteria and Aeromonas. In conclusion, the supplementation of CC in low fish meal diet promoted the growth performance, feed utilization, and both CC and SB supplementation positively modulated the intestinal microorganism community of largemouth bass.