In the bath challenges, there was no clear difference in pathogenicity
between the tested biotype 1 and 2 isolates (Fig. 2). Main
symptoms of the infected fish included dark skin, haemorrhages in the
internal organs and the characteristic haemorrhages in and around
the mouth. The dominant colony type isolated from kidney and spleen
was white and oxidase negative. Reisolated bacteria from the
challenges with biotype 1 were Tween 80-positive and those from
biotype 2 challenges were Tween 80-negative.