"Nytt fra HAVBRUK" newsletter no. 2/2010:
Genetic test finds healthiest fish for breeding
The company Aqua Gen has developed a new genetic test that quickly determines which salmon have the highest resistance to the IPN virus. The recently launched commercial product could mean a breakthrough in the battle against this costly disease.
In 2007, researchers at the Norwegian companies Aqua Gen and Nofima Marin and at the Centre for Integrative Genetics (CIGENE) discovered the markers for a gene that makes salmon more resistant to the virus causing infectious pancreatic necrosis (IPN). The new knowledge about these markers is now being applied to selective breeding – and Aqua Gen is already supplying QTL eggs from parent fish genetically screened for IPN resistance.
There are often multiple genes that play a role in determining an individual’s susceptibility to a certain disease. But in this case, the researchers were very surprised to discover that a single gene largely accounts for the genetic variation in salmon resistance to the IPN virus.
“Remarkably, the gene explains 80 per cent of the variation in resistance to IPN in salmon,” says molecular geneticist and project manager Thomas Moen of Aqua Gen. “We couldn’t believe it when we first discovered this! This gene is nearly as strong a determinant as the one that determines eye colour in humans.”
Discovering such a “powerful” gene enables scientists to select for broodstock with the highest probability of producing offspring that are protected from the IPN virus. The test requires only a blood or tissue sample to indicate the most resistant fish to select.
“The result is very good,” says Dr Moen. “When we select two parent fish with good IPN resistance, their offspring is practically immune to the disease.”
Specialised “QTL eggs” are from parent fish that have tested positive for certain genetic markers so that their offspring inherit a high resistance to IPN. The product, launched in European markets starting in November 2009, could spell good business for Aqua Gen and the industry at large. Aqua Gen is achieving added value of 30-40 per cent on the market compared to conventional products not genetically tested.
“We will be the first breeding company in aquaculture to use DNA for selecting broodstock,” says Odd Magne Rødseth, CEO of Aqua Gen. “This is a new era in selective breeding.” He adds that it is especially satisfying to be involved in something that will promote so much value creation in society.
Improved animal welfare
The method will also advance animal welfare in the aquaculture industry; IPN currently accounts for much of the mortality among production fish stocks, particularly in the early production phases.
Furthermore, genetic testing to select for higher disease resistance will replace conventional challenge testing. In a conventional selective breeding programme, some 80,000 to 100,000 fish in each generation would have to be exposed to the virus.
The long, painstaking process leading to today’s commercial eggs all started with meticulous basic research back in the 1990s.
By the mid-1990s, Aqua Gen had already begun using challenge tests to select for fish with higher resistance to the IPN virus. The Research Council has provided funding for these efforts through projects under the HAVBRUK, Food, and FUGE programmes. The results are presented in the HAVBRUK programme’s latest newsletter (“Nytt fra HAVBRUK” no. 2/2010, available in Norwegian only).
“The price tag for all the research in this area comes to roughly NOK 100 million,” reports Dr Rødseth.
The Aqua Gen CEO is convinced that the company has come so far because it has its own group of researchers.
“It’s worth an enormous amount to have “hands-on” researchers, for both basic and applied research. We would not have been able to accomplish the same job just by hiring in external researchers.”
Searching for the gene
The researchers are still not certain as to exactly which gene it is that gives salmon their immunity to the IPN virus. But this knowledge is also right around the corner.
Efforts to sequence the salmon genome are in full swing now. The sequencing project is a collaborative effort between Canada, Norway and Chile. Norway is providing nearly 40 per cent of the funding through a joint investment by the Norwegian industry and the public funding instruments. An important driving force behind the sequencing is the need to make salmon more resistant to diseases.
“It will be exciting to understand the immune mechanisms involved,” adds Dr Rødseth. “Finding them will have an impact far beyond our selective breeding work. Medicines to combat various viruses are precisely what the world is seeking.”
|220 outbreaks in 2009|
IPN – Infectious pancreatic necrosis. Dreaded by everyone in the salmon production industry, outbreaks of this viral disease can cost dearly in the form of lost fish.
Last year alone, according to the National Veterinary Institute, 220 viral outbreaks of IPN occurred at Norwegian salmon production sites, an increase from 158 outbreaks in 2008. Each year the IPN virus accounts for major losses for salmon farmers in Norway and abroad.
Since IPN strikes the fish in their early life stages, it has proven difficult to develop effective vaccines and vaccination regimes to contain the disease. IPN has been identified in many parts of the world, and has been a major problem in Norway since 1985.
The incidence of the IPN virus is high in both seawater and fresh water. It is found in species as diverse as halibut, cod, eels, octopus, shellfish and crustaceans. Although not every species develops the disease, the many carriers of the virus maintain an elevated pressure of infection in the environment. In salmon, the IPN virus destroys cells that produce digestive enzymes, so even with an apparently steady appetite, infected fish become emaciated by their incapacity to digest fat and protein.
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