We report the first isolation of A. salmonicida subsp. Salmonicida from adult turbot reared in floating cages located near salmonid aquaculture facilities in north-western Spain. The most evident clinical signs in diseased turbot were, a strong abdominal swelling, with accumulation of ascitic fluid, and a pale liver showing petechiae. The total cumulative fish losses in a one-month period in this furunculosis outbreak was 15% of the affected population. Treatment with oxolinic acid was effective in controlling fish mortalities. Virulence tests demonstrated that this bacterium was pathogenic for turbot with an LD50 of 2 x 10(3) cells.