Blood spots in the eye and haemorrhages in the musculature of the caudal peduncle were the main indication of disease in Australian hatchery reared brook trout Salvelinus fontinalis and Atlantic salmon Salmo salar L. Mortalities of 0.1-0.5% per day occurred for 3-4 weeks in fish stocked in circular ponds in the months of February and March when temperatures were falling from 23-11°C. The bacterium belonging to the Family Enterobacteriaceae had similarities with Yersinia ruckeri (the RM bacterium) and Serratia liquefaciens. As a temporary designation SBS were used. It is recommended that its taxonomic position remain sub judice for the present. Inoculation experiments on brook trout and landlocked Atlantic salmon indicated that signs appeared 2-7 days after inoculation and that rainbow trout Salmo gairdneri Richardson were resistant to the disease.