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Diseases of Aquatic Organisms

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DAO 66:121-128 (2005)  -  doi:10.3354/dao066121

Characterisation of atypical Aeromonas salmonicida infection in Arctic charr Salvelinus alpinus and European grayling Thymallus thymallus

Päivi Pylkkö1,2, Tarja Pohjanvirta1, Jari Madetoja1,3, Sinikka Pelkonen1,*

1National Veterinary and Food Research Institute, Kuopio Department, PO Box 92, 70701 Kuopio, Finland
2University of Jyväskylä, Department of Biological and Environmental Sciences, PO Box 35, 40351 Jyväskylä, Finland
3Laboratory of Aquatic Pathobiology, Department of Biology, Åbo Akademi University, BioCity, Artillerigatan 6, 20520 Åbo, Finland
*Corresponding author. Email:

ABSTRACT: Cultured stocks of Arctic charr Salvelinus alpinus and European grayling Thymallus thymallus are vulnerable to infection by achromogenic atypical Aeromonas salmonicida (AAS). In Finland, natural stocks of both fish species have to be supported by restocking, and AAS infection poses a threat to successful restocking because no preventive means are available. In this study, we analysed AAS isolates from Arctic charr and European grayling and from other sources genetically, and characterised the signs and pathology of AAS infection in Arctic charr and European grayling both under farming conditions and after experimental challenge. AAS outbreaks were recorded in 1 fish farm over an 8 yr period. Among various salmonid fishes under farming conditions, only Arctic charr and European grayling were susceptible to AAS infection. The disease caused by AAS could be reproduced in both species using the same AAS strain in an experimental challenge. The course of the disease and pathology of natural and experimental AAS infection differed between the 2 species, even though only 1 strain was used for challenge. Isolates of AAS from Arctic charr and European grayling were genetically identical within a single river water basin. However, genetic heterogeneity was observed among the isolates from different water basins. In both species, AAS caused systemic infection. The results suggest that the same AAS strain could be used to develop a vaccine to protect both Arctic charr and European grayling from AAS infection.

KEY WORDS: Atypical Aeromonas salmonicida · Arctic charr · European grayling · Experimental challenge · Pathology · Pulsed-field gel electrophoresis

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