Effects of luteolin supplementation on growth, histology, antioxidant capacity, non−specific immunity and intestinal microbiota of the red swamp crayfish (Procambarus clarkii)

To investigate the effects of luteolin (LUT) on the growth, antioxidant capacity, non−specific immunity and intestinal microbiota of the red swamp crayfish (Procambarus clarkii), 300 individual P. clarkii (4.17 ± 0.50g average body weight and 50.19 ± 1.40mm average body length) were randomly divided into five groups and fed with LUT doses of 0mg/kg (CG), 50mg/kg (LG50), 100mg/kg (LG100), 300mg/kg (LG300), and 500mg/kg (LG500) for 8 weeks, respectively. Firstly, the results demonstrated that survival rates were significantly higher in all LUT added groups compared to the CG group, with no significant differences in hepatosomatic index, feed coefficient and muscle components. Secondly, dietary supplementation with LUT improves the growth performance of P. clarkii. Thirdly, histological observations displayed that the hepatopancreas and intestine tissues were not damaged in the LUT−supplemented group, and the length of intestinal folds was significantly increased in the LG100 and LG300 groups. Fourthly, the LG50, LG100, and LG300 groups produced significantly increased hepatopancreatic antioxidant enzyme activities and hemolymph immune indicators compared with the CG group. In all experimental groups, malondialdehyde contents were significantly reduced, as were aspartate aminotransferase and alanine aminotransferase activities. Adding LUT to the diet specifically improved the structure and optimized the function of the gut microbiota. Compared to the CG group, the LG group (100mg/kg) displayed a significant increase in the index of Chao1 and Observed species, an increase in the relative abundance of Proteobacteria and Actinobacteria, a decrease in the ratio of Bacteroidetes to Firmicutes, and an increase in the abundance of Thermomonas, Turicibacter, Bdellovibrio and Enterococcus. PICRUSt analysis demonstrated a significant improvement in the KEGG pathway associated with isoflavone biosynthesis in the LG group. In conclusion, the present study confirms that dietary supplementation with 50−300mg/kg LUT favors growth, non−specific immunity and antioxidant function in P. clarkii, with optimal additions ranging from 102−165mg/kg. Furthermore, it optimized gut microbiota function, suggesting that LUT can be used as a potential feed additive for P. clarkii. These findings provide new insights for healthy P. clarkii culture.