Synbiotic administration in Japanese eels with prebiotic 1-kestose and probiotic Lactiplantibacillus plantarum FM8 improved feed efficiency and significantly reduced the levels of Edwardsiella

Bacterial infections are a significant concern in eel aquaculture. Edwardsiella causes severe systemic infections and high mortality rates. This study aimed to demonstrate that synbiotic oral administration could improve eels’ gut environment, health, and aquaculture productivity. After 1 month of administration in Japanese eel Anguilla japonica using synbiotics consisting of prebiotic 1-kestose, a fructooligosaccharide with a degree of polymerization of 3, and the probiotic Lactiplantibacillus plantarum FM8, isolated from fermented food, we discovered that feed efficiency was improved by more than 20%. This may partly be because the synbiotics significantly increased intestinal acetate concentrations (P = 0.0144). 16S rRNA gene amplicon sequencing and linear discriminant analysis effect size revealed that the relative abundance of the Romboutsia was significantly higher, and that of the Edwardsiella was significantly lower in the eel intestine of the synbiotic group (P = 0.0166 and 0.0497, respectively). The BLAST search revealed that all amplicon sequence variants classified as genus Edwardsiella had > 98% identity with the 16S rRNA gene of Edwardsiella tarda, Edwardsiella piscicida, or Edwardsiella anguillarum. Our synbiotic administration in eels exhibited a breakthrough effect in significantly reducing Edwardsiella and increasing acetate concentrations in the intestine, suggesting that our synbiotics could reduce the incidence of eel diseases and improve aquaculture productivity.