Management costs (ca. 10% GVP) associated with AGD are severely limiting further expansion and sustainability of the Tasmanian Atlantic salmon industry. A holistic approach that combines alternative treatments, better management procedures, the use of a vaccine and selection of stock that are more resistant to infection would greatly reduce the impact of AGD. With the exception of selection the other areas are all active components of the Aquafin CRC Health Program. A more resistant stock along with even a partially effective treatment and vaccine would be of major benefit to the long-term sustainability of the industry.
An international consultant recommended to the industry and State Government in March 2003 that a selective breeding program should be established as soon as practical. A business plan for such a program has been developed and is under consideration by the industry. A major trait for inclusion in the program was resistance to AGD. Research in relation to understanding AGD resistance for use in selective breeding was ranked second to oral treatments in an industry survey of AGD priorities in June 2003.
Selection for resistance to external parasites in breeding programs is relatively novel and AGD is an issue specific to the Tasmanian industry, therefore unlike most other production traits in a breeding program reliance on overseas research and experience is impossible. With recent advances in molecular technologies it is now possible to investigate and understand variation to disease at the genetic level. Such knowledge on AGD will allow both improved understanding of the phenotypic variation (that will benefit other research areas) and identification of specific genetic markers that would allow faster genetic gains in resistance to be made in a selection program than would be possible via standard phenotypic selection alone.
Final report
The outcome of this project is the development, at the request of industry, of a proposal to enhance the genetic gains in the industry selective breeding program for AGD resistance through marker assisted selection. The confidence to proceed with such a proposal is brought about by the extensive knowledge and understanding gained on the molecular basis of AGD resistance through this project.
The project completed the first comparison of genetic variation at a coding gene between the domesticated Australian Atlantic salmon and their ancestral Canadian population; results were also compared to that published for European populations.
In contrast to previously reported variation at non-coding microsatellite loci, a high level of variation at the major histocompatibility (MH) genes was observed within the domesticated Australian population, and observed sequence diversity exceeded that reported for other cultured Atlantic salmon populations.
The project also completed the first study to examine resistance to AGD at a molecular level. The association between MH polymorphism and severity of AGD infection was examined in 30 full-sibling families by acute challenge.
Keywords: Atlantic salmon, Salmo salar, amoebic gill disease, AGD, Neoparamoeba, resistance, gene expression, DNA microarray.