New DNA test for escaped salmon

April 7, 2014 - 06:59

Scientists have developed a new DNA test for escaped salmon that makes it easy to track down the responsible fish farm.

Escaped farmed salmon threatens wild salmon. (Photo: Microstock)

Escaped salmon from fish farms are considered to be a major problem since they present a threat for the wild salmon populations.

It is therefore on the researchers agenda to find ways to efficiently connect the escaped fish to it’s farm.

“The advantage of this tracing system is that only the parents of the production fish need to be tested,” says Celeste Jacq at the Norwegian food research institute Nofima.

Jacq has developed and validated the new DNA test together with colleague Matthew Baranski.

The parents
The laboratory equipment is easy to use in sampling conditions and minimizes the risk of incorrect recording by the samplers.

By taking samples of the parent fish, which counts about 30-40,000 fish at the roe producers, the scientists obtain an overview of the DNA profile of 350 million farmed salmon – the total number of salmon currently in Norwegian cages.

Every fish has a unique DNA fingerprint, and by using the marker set, the scientists can link an offspring back to the parent fish.

Nofima has used the set of markers in several tests of farmed fish with known pedigree, and have confirmed that they have found the correct parents of each individual farmed fish. They have also taken tests of wild fish, and these tests have confirmed the results – they did not match the DNA of the parents of the farmed fish.

By allowing a certificate of traceability to accompany the roe via the hatchery to the sea-based fish farm, the scientists also have a complete overview of where the offspring grow up.

There are 350 million farmed salmon currently in Norwegian fish farms (Photo: Eugene Sergeev, Microstock)

When an escaped farmed salmon is found in the river, only a DNA analysis of this particular salmon is required in order to find out which fish farm it comes from.

Trace in time and space

DNA markers have been used for several years to identify escaped farmed salmon.

Nevertheless, with this DNA test, the fish may be traced in terms of both time and space.

The set of markers may also be used to avoid crossbreeding of siblings in stock enhancement programmes in rivers in order to minimize inbreeding.

Jacq believes DNA tracing must be used in combination with marking that is physically visible such as adipose fin clipping of all production fish. This would enable someone to distinguish a farmed fish from a wild fish on the riverbank before any DNA test is taken.

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Side story: Following the gene trail

In order to follow the gene trail from an escaped fish to the responsible owner, the scientists need to record the genotypes of the parents of all the farmed salmon. This is achieved by cutting off their adipose fins and analysing the DNA.

The parents of the farmed salmon may be found at the breeding company’s roe producers, where a male salmon is crossed with one or more female salmon. The offspring of each specific set of parents has a unique DNA profile, and by sending all fertilised eggs from one set of parents or parental group to a smolt producer along with a certificate of traceability, all fish from each smolt producer can receive a unique DNA profile. This will follow the fish when it is later transferred to a sea cage. The DNA profile will be stored in a national database so that the fish in the cage do not need to be tested in the event of suspicion of escaping.

DNA analysis of an escaped salmon will therefore match the gene profile of only one responsible company.

Nofima is a business oriented research institute working in research and development for the aquaculture, fisheries and food industry in Norway. Read more

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