Amoebic gill disease (AGD) first emerged as a problem in the
1980’s in Tasmania; it is now a disease of international significance. AGD has
now been identified on the west coast of USA, Chile, New Zealand, Japan, South
Africa, Ireland, Scotland, France, Spain and Norway.
Current methodologies of controlling this disease involve
bathing the fish in either freshwater for an extended period of time; or in hydrogen
peroxide for a short period of time.
Despite the fact that AGD has been around for several
decades, there are still significant gaps in our knowledge about this disease.
The causative agent was only identified relatively recently. In order for us to
develop more effective control strategies
for AGD, we need to improve our knowledge of the organism itself and the
epidemiology of the disease. As examples – where does the amoeba live when a
site is fallowed? Does it have a reservoir in wild populations of fish? Can it
live independent of a host, for how long? What depths does it prefer? Is it
phototactic? What environmental conditions favour amoeba proliferation? Does
AGD have a link with biofouling or harmful algae? Under normal culture
situations, Chinook salmon are immune to AGD, why? Will ingredient substitution
in the feed have any influence on AGD?
AGD has now been a serious salmon farming issue for 30 years, and we
have still a long way to go before we have total understanding of the disease
we are trying to defeat.