Abstract
Effects of the time-lag between the exposures of fish (loach) to Flexibacter columnaris and a competitive bacterium, Citrobacter freundii on the invasion by F.columnaris were investigated.It was found that the competitor could prevent invasion of the fish by F.columnaris if it was added within 1/2h after exposure to F.columnaris. In this case, F.columnaris failed to increase in number on the body surface of fish and water environment. The invasion of fish by F.columnaris did not occur when C.freundii was added prior to F.columnaris. On the other hand, F.columnbris was able to establish itself on the body of fish and successfully invaded fish when the competitor was added 1h or later after exposure of the fish to F.columnaris. In that case, the number of F.columnaris on the body surface as well as in the water environment gradually increased. The number of C.freundii on the body surface increased initially but decreased after 48h of exposure. In the water environment, C.freundii did not significantly vary in number.
