Abstract.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 troutSalvelinus fontinalis(Mitchill) and Atlantic salmonSalmo salarL. 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 withYersinia ruckeri(the RM bacterium) andSerratia liquefaciens. As a temporary designation SBS was used. It is recommended that its taxonomic position remain subjudicefor the present. Inoculation experiments on brook trout and landlocked Atlantic salmon indicated that signs appeared 2–7 days after inoculation and that rainbow troutSalmo gairdneriRichardson were resistant to t