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Diseases of Aquatic Organisms

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DAO 93:51-61 (2010)  -  DOI:

Previously unrecognised division within Moritella viscosa isolated from fish farmed in the North Atlantic

S. Grove1, C. R. Wiik-Nielsen1, T. Lunder3,6, H. S. Tunsjø2, N. M. Tandstad1, L. J. Reitan1, A. Marthinussen4,7, M. Sørgaard1, A. B. Olsen5, D. J. Colquhoun1,*

1National Veterinary Institute, Oslo, PO Box 8156 Dep, 0033 Oslo, Norway
2Norwegian School of Veterinary Science, PO Box 8146, 0033 Oslo, Norway
3ScanVacc AS, PO Box 233, 2151 rnes, Norway
4Ler¿y Hydrotech AS, Bentnesveien 50, 6512 Kristiansund, Norway
5National Veterinary Institute, Bergen, PO Box 1263 Sentrum, 5811 Bergen, Norway
6Present address: Novartis Aqua Norway, PO Box 237 ¯kern, Oslo, Norway
7Present address: Aqua Gen AS, PO Box 1240, 7462 Trondheim, Norway
*Corresponding author. Email:

ABSTRACT: Previously undocumented phenotypical and genetic variation was identified amongst isolates of Moritella viscosa collected from various geographical locations and from different fish species. The studied isolates could be split into 2 major phenotypically and genetically different clusters, one of which was consistent with the species type strain (NCIMB 13548). Isolates consistent with the type strain originated exclusively from Atlantic salmon farmed in Norway, Scotland and the Faroe Isles, although a single isolate from farmed Norwegian cod clustered closely with this group. The 'variant' cluster comprised isolates originating from Norwegian farmed rainbow trout, Icelandic farmed rainbow trout and salmon, Canadian farmed (Atlantic) salmon, Icelandic lumpsucker and only exceptionally from Norwegian salmon. With the exception of the single aforementioned cod isolate, all isolates from Norwegian farmed cod belonged to the variant cluster. Phenotypically, the clusters could be absolutely separated only by elevated haemolytic activity in the variant strain, although approximately half of these isolates also produced acid from mannose, in contrast to the typical (type) strain. While 16S rRNA gene sequencing was unable to separate the 2 clusters, Western blot analyses, plasmid profile analysis, pulsed field gel electrophoresis and gyrB gene sequence analysis produced clusters consistent with the phenotypic data. Macroscopically and histologically the disease in rainbow trout caused by the variant strain was consistent with that previously described in Atlantic salmon. The results of the present study may indicate a degree of host specificity of the typical strain for Atlantic salmon.

KEY WORDS: Rainbow trout · Atlantic salmon · Oncorhynchus mykiss · Salmo salar · Gadus morhua · Moritella viscosa · Cyclopterus lumpus · Winter-ulcer

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Cite this article as: Grove S, Wiik-Nielsen CR, Lunder T, Tunsjø HS and others (2010) Previously unrecognised division within Moritella viscosa isolated from fish farmed in the North Atlantic. Dis Aquat Org 93:51-61.

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