Abstract
BackgroundFurunculosis, caused by Aeromonas salmonicida, continues to be a major health problem for the growing salmonid aquaculture. Despite effective vaccination programs regular outbreaks occur at the fish farms calling for repeated antibiotic treatment. We hypothesized that a difference in natural susceptibility to this disease might exist between Baltic salmon and the widely used rainbow trout.Study DesignA cohabitation challenge model was applied to investigate the relative susceptibility to infection with A. salmonicida in rainbow trout and Baltic salmon. The course of infection was monitored daily over a 30-day period post challenge and the results were summarized in mortality curves.Results A. salmonicida was recovered from mortalities during the entire test period. At day 30 the survival was 6.2% and 34.0% for rainbow trout and Baltic salmon, respectively. Significant differences in susceptibility to A. salmonicida were demonstrated between the two salmonids and hazard ratio estimation between rainbow trout and Baltic salmon showed a 3.36 higher risk of dying from the infection in the former.ConclusionThe finding that Baltic salmon carries a high level of natural resistance to furunculosis might raise new possibilities for salmonid aquaculture in terms of minimizing disease outbreaks and the use of antibiotics.
Highlights
The bacterial disease furunculosis caused by Aeromonas salmonicida is one of the main concerns in European salmonid mariculture due to high mortality rates and significant economic losses [1,2]
Significant differences in susceptibility to A. salmonicida were demonstrated between the two salmonids and hazard ratio estimation between rainbow trout and Baltic salmon showed a 3.36 higher risk of dying from the infection in the former
The finding that Baltic salmon carries a high level of natural resistance to furunculosis might raise new possibilities for salmonid aquaculture in terms of minimizing disease outbreaks and the use of antibiotics
Summary
The bacterial disease furunculosis caused by Aeromonas salmonicida is one of the main concerns in European salmonid mariculture due to high mortality rates and significant economic losses [1,2]. Recent studies have shown that the isolated salmon stock in the Baltic possesses genes conferring resistance towards the extremely pathogenic parasite Gyrodactylus salaris [6,7,8]. EastAtlantic salmon (Norwegian, Scottish, and Danish) are very susceptible to G. salaris and show no effective immune response during infection [6,7,8,10,13] These differences between salmon stocks regarding protective immunity against the very pathogenic G. salaris pose the question whether a comparable difference might exist when it comes to infection with the bacterium A. salmonicida. A population of East-Atlantic salmon naturally infected with A. salmonicida was used as disease carriers in a cohabitation study to test for differences in susceptibility to furunculosis between Baltic salmon and rainbow trout. We hypothesized that a difference in natural susceptibility to this disease might exist between Baltic salmon and the widely used rainbow trout
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