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.
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):
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