The possibility of transmission of Aeromonas salmonicida subsp. salmonicida from Atlantic salmon Salmo salar to cod Gadus morhua, halibut Hippoglossus hippoglossus and wrasse (Labridae) was studied in both laboratory cohabitation and injection challenge trials, and in a field situation during an outbreak of furunculosis in Atlantic salmon in 2 sea farms containing both cod and salmon. A. salmonicida was isolated from cod, halibut and wrasse, but only occasionally. The injection challenge studies with A. salmonicida subsp. salmonicida were carried out on cod and halibut. The results suggest that A. salmonicida subsp. salmonicida can be transmitted from salmon and cause disease in cod, halibut and wrasse, but that this is a relatively rare event. Shortened abstract.