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 red swamp crayfish (Procambarus clarkii), 300 individual crayfish (4.17 +/- 0.50 g average body weight and 50.19 +/- 1.40 mm average body length) were randomly divided into five groups and fed with LUT doses of 0 mg/kg (CG), 50 mg/kg (LG50), 100 mg/kg (LG100), 300 mg/kg (LG300), and 500 mg/kg (LG500) for 8 weeks, respectively. Firstly, the results demonstrated that the survival and growth performance were significantly improved in all LUT added groups compared to the control (CG group), with no significant differences in hepatosomatic index, feed coefficient and muscle components, and the crayfish in LG100 group showed the maximal survival rate (SR) and specific growth rate (SGR) (P < 0.05). Secondly, histological observations displayed that the hepatopancreas and intestine tissues were not impacted in the LUT-supplemented groups, and the length of intestinal folds was significantly increased in LG100 and LG300 groups. Thirdly, LG50, LG100, and LG300 groups produced significantly increased hepatopancreatic antioxidant enzyme activities and hemolymph immune indicators compared with the control. In all experimental groups, malondialdehyde (MDA) contents were significantly reduced, as were aspartate aminotransferase and alanine aminotransferase activities. Lastly, dietary LUT specifically improved the structure and optimized the function of the gut microbiota. Compared to the control, the LG100 group 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 50-300 mg/kg LUT favors growth, non-specific immunity and antioxidant function in P. clarkii, with optimal additions ranging from 102-165 mg/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 crayfish 's healthy culture.