The effects of bamboo leaf flavonoids on growth performance, immunity, antioxidant status, and intestinal microflora of Chinese mitten crabs (Eriocheir sinensis)

Bamboo leaf flavonoids (BLF) are the mainly bioactive constituents of bamboo leaves and have caused considerable attention for antibacterial, anti-inflammatory, antioxidant, antitumor, and anti-aging activities. This research evaluated dietary (commercial pellet feed form) addition of Phyllostachys BLF effects on growth, non-specific immunity, antioxidant function, and intestinal microflora of Chinese mitten crabs. A total of 216 crabs were randomly sorted into 18 tanks with 6 replicates for each group and 12 crabs per replicate. Crabs were fed with a basal diet supplemented with 0 (control), 500, and 1000 mg/kg BLF, respectively. Results shown that crabs fed diet supplemented with 1000 mg/kg BLF improved the growth performance, enhanced serum phenoloxidase (PO), lysozyme, total antioxidant capacity (T-AOC), and glutathione peroxidase (GPx) levels, increased hepatopancreas T-AOC and total superoxide dismutase (T-SOD) levels, upregulated hepatopancreas Tube and Dif mRNA expression levels compared with the crabs in the control (P < 0.05). The inclusion of 500 mg/kg BLF only increased the serum lysozyme content (P < 0.05). Dietary 500 or 1000 mg/kg BLF addition increased serum T-SOD and catalase activities, enhanced hepatopancreas GPx activity, reduced the serum malondialdehyde content, upregulated the mRNA expression levels of hepatopancreas GPx, toll-like receptors 1, myeloid differentiation factor 88, lysozyme, and prophenoloxidase of crabs (P < 0.05). Crabs in 1000 mg/kg BLF addition group had higher PO activity than that crabs in the 500 mg/kg BLF addition group (P < 0.05). The separated principal co-ordinates analysis revealed that the three groups had different microbiota composition. Both 500 and 1000 mg/kg BLF addition decreased the shannon and chao1 indexes, reduced the abundance of phyla Bacteroidota, enhanced the abundance of phyla Firmicutes and genus Candidatus_Bacilloplasma in intestine microbiota of Chinese mitten crabs (P < 0.05). In conclusion, dietary BLF inclusion improved the growth performance and intestinal microflora, enhanced the non-specific immunity and antioxidant function, activated the Toll/NF-κB pathway in Chinese mitten crabs.