Effects of Macleaya cordata extract on intestinal microbiota of European eels (Anguilla anguilla) cultured in cement tanks

This trial investigated the effects of Macleaya cordata extract (MCE) on the diversity and composition of the intestinal microbiota of European eels ( Anguilla anguilla ) cultured in cement tanks. After routine grading eels, six cement tanks with similar body size and fish weight (about 167 g/fish and 3620 kg/tank) were randomly divided into the control and MCE groups. The control group was fed a commercial diet, and the MCE group was fed the same commercial diet supplemented with 100 mg/kg MCE. There were three tanks in each group. This trial lasted for six weeks. Compared with the control group, the European eels in the MCE groups had a higher richness and diversity of intestinal microbiota. At the phylum level, European eels in the MCE group had higher relative abundances of Firmicutes and Proteobacteria and lower relative abundance of Spirochaetae and Fusobacteria compared to those of the control group. At the genus level, the European eels in the control group had higher relative abundances of Streptococcus and Legionella . In comparison, the relative abundances of Bacillus , Anaerobacillus , and Sphingomonas were higher in the intestine of the European eels of the MCE group. In conclusion, the dietary 100 mg/kg MCE supplementation might beneficially change the intestinal microbiota of European eels by increasing the relative abundance of certain probiotics and inhibiting some pathogenic bacteria.