Experimentally induced marine flexibacteriosis in Atlantic Salmon smolts Salmo salar. I.: Pathogenicity

<i>Tenacibaculum maritimum</i> causes marine flexibacteriosis in many cultured fish species, including Atlantic salmon <i>Salmo salar</i> in Tasmania, Australia. Several aspects of the pathogenicity of this bacterium were investigated in naive Atlantic salmon smolts using different isolates, growth conditions and doses to produce a model of infection. We found that <i>T. maritimum</i> is pathogenic to Atlantic salmon using either marine Shieh’s or marine Ordal’s culture medium. The use of aeration in broth culture produced a dose effect in challenge due to a ‘clumping’ of the bacteria during culture. The virulence of a strain appears to be connected with this ‘clumping’; the more adherent the cells, the more pathogenic the strain. Differences in virulence between 3 strains was apparent, with 1 of the strains (89/4747) being non-pathogenic and unable to produce disease in the host. The 2 other strains (89/4762, 00/3280) were highly virulent, resulting in 100% mortalities within 3 d. A reproducible model of infection has been established in the present study using strain 89/4762. Results from the present study provide a better insight into the nature of the disease.