Edwardsiella tarda in Eel Culture Environment

Abstract

Edwardsiella tarda has been known as the causative bacterium of paracolo-disease (edwardsiellosis)in cultured eels in Japan. However, the ecology of the pathogen in eel culture ponds has not been fully investigated so far.
Field surveys on the presence and abundance of E. tarda in water and mud of eel culture ponds in Tokushima Prefecture were made at four seasons from 1981 to 1982 by a modification of the detection method described by WYATT et al.(1979). The incidence of E. tarda in water(W)and mud(M)samples from some 30 ponds were 90%(W)and 91%(M)in summer, 97%(W)and 100%(M)in autumn, 48%(W)and 25%(M)in winter, and 73%(W)and 75%(M)in spring. The number of the organism also increased during the warmer seasons.
From the results of intramuscular injections into Japanese eels(Anguilla japonica), 37 strains out of 159 strains of E. tarda isolated from water and mud samples were proved virulent. Although these virulent strains shared common O-antigens with each other, they were divided into 2 serotypes based on a bsorption tests. About one-third of the avirulent strains also agglutinated with rabbit O-antisera against the virulent strains.