Isolation and characterization of a highly virulent Edwardsiella piscicida strain responsible for mass mortality in marbled eel (Anguilla marmorata) cultured in Korea

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Edwardsiella infections have the potential to induce immense economic losses by affecting multiple fish species, and have been increasingly reported in aquaculture. Edwardsiella tarda, Edwardsiella hoshinae, and Edwardsiella ictaluri have all been previously associated with mass mortality. Recent technological advances in bacterial identification have identified E. piscicida and E. anguillarum as important pathogens affecting global fisheries. Strains previously identified as E. tarda have been re-grouped based on new sequence data and phylogenetic studies. E. piscicida was classified as a novel species in 2012 and has since been reported to have caused mortality in diverse fish species in numerous countries that are potentially more threatening than the mortality caused by E. tarda. Eels are one of the most consumed fish species in Asia, and Anguilla japonica is a commonly reared species in fisheries. However, due to increasing global eel consumption, attempts to culture marbled eel (A. marmorata) have been recently carried out in many Asian countries including Korea. The external clinical signs of Edwardsiella piscicida- infected marbled eel (A. marmorata) were enlarged liver, hemorrhagic congestion at the base of fins and on the skin, as well as hemorrhagic ascites and multifocal abscesses were found in the liver. Histopathology on E. piscicida- infected tissues revealed bacteremia, multifocal necrotizing hepatitis with vasculitis and splenitis with vasculitis. This study reports the first E. piscicida infection case responsible for mass mortality in A. marmorata cultured in Korea. Our study focused on the isolation and histopathological characterization of this bacterial strain to better understand its damage on A. marmorata.