Isolation and Identification of an Atypical Aeromonas salmonicida Strain Causing Epizootic Losses Among Atlantic Salmon (Salmo salar) Reared in a Nova Scotian Hatchery

The bacterium causing 50% cumulative mortality among postyearling parr (pyp) Atlantic salmon (Salmo salar) reared at a Nova Scotian hatchery was identified to be an atypical, achromogenic Aeromonas salmonicida strain. This organism, although differing in several biochemical reactions from typical A. salmonicida, was sensitive to A. salmonicida bacteriophages. Antigenically, the Kejimkujik A. salmonicida was indistinguishable from typical A. salmonicida strains when the serological relatedness was examined using cross-adsorbed rabbit antisera. Analysis of DNA from the atypical A. salmonicida yielded a % GC value of 57.85, a value within the range expected for A. salmonicida.Key words: atypical, Aeromonas salmonicida, Atlantic salmon