Abstract
In 2012, a freshwater farm in south China experienced a severe disease outbreak in cultured giant mottled eel Anguilla marmorata, resulting in high mortality. The diseased eels showed extreme ulcerative injuries throughout their bodies and obvious swelling of the liver and body kidney. A pure culture of a bacterial strain, designated HZHM, was isolated and identified as Edwardsiella tarda based on its physiological and biochemical characteristics and on phylogenetic analysis of 16S rRNA and fimbrial genes. The HZHM strain was unable to produce hydrogen sulphide (H2S) from thiosulphate in biochemical testing. In addition, results of the challenge trial confirmed that the HZHM strain was virulent for A. marmorata, with an LD50 value of 1.3 × 106 colony-forming units (CFU). Histologically, severe hemorrhage occurred in most organs, increased melano-macrophage reaction was observed in the spleen and body kidney, and cytoplasmic vacuolation and liquefactive necrosis were found in the brain. To our knowledge, this is the first report of E. tarda-associated pathogenicity in A. marmorata.
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