Susceptibility of Japanese Medaka to Edwardsiella piscicida and E. anguillarum Isolated from Aquacultured Fish

Abstract

Edwardsiella bacteria infect Japanese medaka Oryzias latipes; however, the difference in susceptibility between E. piscicida and E. anguillarum is unknown. In this study, we performed challenge tests with medaka using four Edwardsiella strains, which were difficult to be identified by specific primers. The four strains were reclassified as three E. piscicida strains and one E. anguillarum strain using phylogenetic analysis. The immersion challenge demonstrated that medaka were more susceptible to E. piscicida than to E. anguillarum. Increases in the bacterial copy number in the infected medaka kidneys were correlated with the worsening of the external symptoms. Medaka is considered a valuable model organism for understanding the etiology of edwardsiellosis.