Furunculosis, Aeromonas salmonicida & Fish Farming

The disease furunculosis caused by the bacteria Aeromonas salmonicida, continues to be a major health problem for the growing salmonid aquaculture. Continuing to raise high concerns in European salmonid fishfarms due to high mortality rates leading to detrimental economic losses.

In spite of effective vaccination programs frequent outbreaks occur at the fish farms calling for repeated antibiotic treatment. However, side effects following oil-adjuvanted vaccination have raised a series of ethical and welfare questions connected to the use of vaccines. Additionally antimicrobial residues left from treating out breaks can persist in the environment and lead to resistance spreading to other microbes.

Lars Holten-Andersen et al (2012) hypothesized that a difference in natural susceptibility to this disease might exist between Baltic salmon and the widely used rainbow trout. The researchers tested the hypothesis using a cohabitation challenge model; this was used to investigate the relative susceptibility to infection with A. salmonicida in rainbow trout and Baltic salmon. They monitored the course of the infection on a daily basis over the course 30-day period post challenge summerising the results as mortality curves.

The cohabitation infection model proved to be effective in terms of disease

transmission. Bacteriological examinations provide confirmation that the mortalities occurred as a result of the infection. This verifies the transmission of the disease from East-Atlantic salmon to Baltic salmon and rainbow trout.  Lars Holten-Andersen and co found that survival at day 30 was 6.2% and 34.0% for rainbow trout and Baltic salmon, respectively.  The differences in susceptibility to A. salmonicida were significant between the two salmonids. The risk of dying from the infection was found to be 3.36 higher Baltic salmon compared to rainbow trout.

FINAL NOTES:

Studies such as this one provide valuable data and evidence that we can use to make better-informed decisions in the future. For example, which particular species of fish would one select for cultivation? If a fish already possessing naturally high resistance was selected this might enable us to reduce the amount of antibiotic residues left in the environment do to lower frequencies of outbreaks. 

Full article here :) 

Holten-Andersen L, Dalsgaard I, Buchmann K (2012) Baltic Salmon, Salmo salar, from Swedish River Lule A ̈ lv Is More Resistant to Furunculosis Compared to Rainbow Trout. PLoS ONE 7(1):