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Potential risk factors of amoebic gill disease in Tasmanian Atlantic salmon


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Bagley, Carley Anderson 2006 , 'Potential risk factors of amoebic gill disease in Tasmanian Atlantic salmon', PhD thesis, University of Tasmania.

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Amoebic gill disease (AGD) is the most significant health problem affecting the
production of Atlantic salmon (Salmo salar L.) in Tasmania, Australia. AGD
affects a number of cultured fish species worldwide, however its impact is
insignificant when compared to that in Tasmania. The disease was first identified
in southern Tasmania in 1986 shortly after the initiation of Atlantic salmon
farming. AGD is a result of an endemic parasite Neoparamoeba sp. attaching to
the salmon's gill tissue. Research conducted over the years has resulted in a large
reduction of AGD associated mortalities. However, the disease continues to place
a significant financial burden on the industry with the only effective form of
treatment being freshwater baths, a strategy implemented in the late 1980's.
Epidemiological studies are essential as they facilitate in identifying causal factors
that may be associated with disease outbreaks. An understanding of these complex
interactions is required in order to implement effective control and prevention
strategies. This thesis examined a number of environmental conditions and
husbandry protocols currently utilised in the Atlantic salmon industry in Tasmania.
Fallowing of lease sites as a disease management strategy for AGD was found to
be unsuccessful. The mean AGD prevalence of Atlantic salmon cultured at a
fallowed site (57.5% ± 5.32) was similar to fish at the control site (52.3% ± 5.35).
Neoparamoeba sp. was isolated from environmental samples at the fallowed site
despite the absence of salmon. Atlantic salmon maintained in copper based
antifouling paint treated nets had a higher mean prevalence of AGD (29 .2% ±
6.74) compared to salmon maintained in untreated nets (21.3% ± 6.43). The belief
that copper acts as an attractant for Neoparamoeba sp. was not ascertained.
Atlantic salmon maintained under continuos artificial lights had a similar
prevalence of AGD as salmon maintained under natural light conditions for the
majority of a 12 month trial. However when subjected to stressful conditions the
salmon maintained under artificial lights had a significantly higher percentage of
gill lesions (43.1 % ± 4.38) compared to salmon held under natural light conditions
(14.11%± 1.96). An Atlantic salmon farm located in the Tamar River in the north of Tasmania was
studied as a control site, as the farm had been operating for approximately 5 years
with no history of AGD. Neoparamoeba sp. was isolated from the benthic
sediment and nylon nets, but not detected on steel nets or the salmon's gills.
However approximately 12 months after the trial concluded the farm experienced
its first outbreak of AGD.
The work contained in this thesis has identified a number of environmental and
husbandry practices that warrant further investigation to accurately understand
their influence on the occurrence of AGD in Tasmanian cultured Atlantic salmon.
Future research must also concentrate on identifying and understanding the
causative agent/s involved in this disease in order to develop effective treatments.

Item Type: Thesis - PhD
Authors/Creators:Bagley, Carley Anderson
Keywords: Atlantic salmon, Atlantic salmon, Fishes, Atlantic salmon fisheries, Gills, Salmon farming
Copyright Holders: The Author
Copyright Information:

Copyright 2006 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Available for library use only and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2006. Includes bibliographical references

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