Evidence that superficial branchial colonies on the gills of Salmo salar L. are not Aeromonas salmonicida

Abstract. The indirect immunoperoxidase technique (IPT) was used to examine specific superficial colonies of organisms observed on the gills of salmonids. The evidence obtained suggested that the superficial colonies were not a form of Aeromonas salmonicida , the causative agent of furunculosis. Application of the IPT to bacterial smears and previously stained histological sections from a case of furunculosis, confirmed the sensitivity of the technique and suggested the presence of common antigens between A. salmonicida and members of the Vibrionaceae, Pseudomonaceae and Enterobacteriaceae.