Abstract
Edwardsiellosis in the red seabream Pagrus major is one of the most significant bacterial infections in Japanese marine aquaculture. In this study, we investigated whether fish carcasses harboring Edwardsiella anguillarum (the causative agent of edwardsiellosis) serve as a source of infection using three experimental infection trials. In Experiment 1, healthy red seabream exhibited scavenging behavior on infected carcasses, resulting in increased E. anguillarum concentrations (viable counts and environmental DNA) in the rearing water and the bacterial detection in the intestines. This bacterium was subsequently isolated from the trunk kidney of fish in the same tank, and the fish developed edwardsiellosis. In Experiment 2, fish were infected with E. anguillarum through cohabitation with infected carcasses. Higher infection ratios were observed in the group with scavenging access to the carcasses than in the group without. In Experiment 3, oral administration of either an E. anguillarum suspension or a kidney homogenate from diseased fish successfully induced infection. In conclusion, infected fish carcasses may serve as a reservoir of E. anguillarum, with scavenging behavior playing a critical role in edwardsiellosis transmission in red seabream farms by contributing to both the release of the bacterium into surrounding water and the oral consumption of infected tissues.
