Flexibacter psychrophilus (syn. Cytophaga psychrophila) was isolated in Tasmania, Australia, from farmed Atlantic salmon Salmo salar with moderate to severe erosion of the fins; there was no evidence of skin lesions. The mortality level in the population of affected fish was less than 0.01%/wk, but the morbidity level was in excess of 80%. The phenotype of the Australian isolates is in good agreement with strains from Europe and North America and differs only in that the Australian isolates produced a brown pigmentation on tyrosine agar and did not hydrolyse Tween 80. The growth in vitro of all isolates was inhibited by acriflavine, ampicillin, and oxolinic acid at concentrations in excess of 0.5 mu g/ml and by oxytetracycline at 1.56 mu g/ml; none of the isolates were inhibited by sulphamethazine or trimethoprim at 25 mu g/ml.