Abstract
An infection experiment revealed that the level of secondary bacterial infection increased after parasitization by Argulus coregoni. Fifty juvenile masu trout (Oncorhynchus masou) (30-50 g/fish) and 500 A. coregoni were kept in a container supplied with running water at 13°-15°C contaminated with viable cells of Aeromonas salmonicida, “furunculosis” agent. The other 50 O. masou free from the parasite were used as a control. The fish infected by A. coregoni showed significantly higher mortality than the control fish. The autopsy revealed that external lesions of furunculosis occurred in all parts of the body and were slightly more abundant in the posterior half of the body of both infected and uninfected fishes. In addition, the infected fish had more extensive lesions than the uninfected. However, no definite correlation was detected between the site of the external lesions and that of attachment of A. coregoni.
