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Molecular assessment of resistance to amoebic gill disease


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Wynne, James Watkin 2008 , 'Molecular assessment of resistance to amoebic gill disease', PhD thesis, University of Tasmania.

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Amoebic gill disease (AGD) is the most significant health issue affecting the culture of
Atlantic salmon (Salmo salar L.) in Tasmania, Australia. Recent research has suggested
that heritable variation in AGD resistance exists within the Tasmanian Atlantic salmon
population. Subsequently, enhancing this resistance through selective breeding has
become a major research focus in Tasmania. The mechanisms controlling this
commercially important trait remain poorly understood. To this end, an investigation of
the molecular mechanisms controlling AGD resistance was conducted.
Due to their high polymorphism and important immune function genes of the major
histocompatibility complex (MHC) - known as the MH genes in Atlantic salmon -
represent some of the best candidate loci with a possible influence upon AGD
resistance. With this in mind, the amount of MH variation and its association with
resistance to AGD was investigated. In contrast to what has been previously reported at
non-coding microsatellite loci, a high level of MH class II diversity has been maintained
in the Australian Atlantic salmon population compared to the ancestral population. The
use of an AGD challenge test with subsequent MH genotyping demonstrated that the
presence of one MH class II alpha allele known as Sasa-DAA-3UTR 239 was
significantly associated with reduced disease severity. Individuals containing a copy of
this allele had 4.0% less gill filaments infected by AGD compared to individuals
without this allele.
Next utilising a cDNA microarray with real-time PCR verification the transcriptional
changes associated with AGD and AGD resistance were investigated. Comparing the
gene expression profiles within the gill, liver and anterior kidney between naive and
AGD affected (at 19 days post inoculation) Atlantic salmon suggests the host response
to AGD upon acute first infection is largely suppressive and localised to the site of
infection, the gill. Next, the gill transcriptome response between Atlantic salmon
deemed putatively resistant and putatively susceptible to AGD following chronic
natural infection was investigated. Results suggested that compared to the susceptible
individuals, Atlantic salmon resistant to AGD demonstrate an up-regulation of adaptive
immune genes and negative regulators of the cycle cell. Further characterisation of the
full length mRNA sequence and expression distribution of one unknown transcript
which was significantly up-regulated in both previous microarray experiments was
This research has provided the first molecular assessment of resistance to AGD in
Atlantic salmon. The implications of this research in terms of the understanding of the
molecular mechanisms of AGD resistance and the ultimate development of genetic
markers linked to resistance will be considered.

Item Type: Thesis - PhD
Authors/Creators:Wynne, James Watkin
Keywords: Atlantic salmon, Fishes, Atlantic salmon fisheries, Gills, Salmon farming
Copyright Holders: The Author
Copyright Information:

Copyright 2008 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, 2008. Includes bibliographical references. Ch. 1. General introduction -- Ch. 2. Diversity at the MH class II within domesticated Australian Atlantic salmon -- Ch. 3. MH polymorphism associated with resistance to AGD in Atlantic salmon -- Ch. 4. Transcriptome analyses of AGD affected Atlantic salmon reveals localised host gene suppression -- Ch. 5. Transcriptome profiling AGD resistant Atlantic salmon -- Ch. 6. Further investigation of the unknown transcript CK880278 -- Ch. 7. General discussion

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