Aquaculture for all

Gene Flow from Farmed to Wild Salmon

Salmonids Husbandry Breeding & genetics +1 more

Wild salmon are done spawning in the rivers for this year, but a few too many farmed salmon have escaped from their cages, spreading their roe and milt, writes Reidun Lilleholt of Nofima.

As a result, some farmed salmon have crossed their genes with locally adapted wild salmon. How does this affect the ability of wild salmon to survive in the rivers?

Researchers at Nofima want to uncover the gene flow that actually occurs from farmed salmon to wild salmon.

16,000 markers

Salmon eggs

The Norwegian Centre for Integrative Genetics (CIGENE) and Nofima recently concluded their work on creating a chip that contains markers for 16,000 salmon genes. These genes do not affect the characteristics of the fish, but some of them are connected to functional genes that code for characteristics that play a vital role in salmon farming, such as growth and health. The characteristics important for farmed salmon are not necessarily the same ones that are important for wild salmon.

"We will use this chip to find the functional genes for important characteristics in farmed salmon and map the changes in them. Then we will investigate whether changes occur in these particular genes in the wild salmon stock," explains Sten Karlsson of Nofima. This will tell researchers how great the genetic impact of escaped farmed salmon actually is.

Survival of the fittest

In about 1970, wild salmon were genetically identical to farmed salmon. After eight generations of salmon, however, farmed salmon have developed a genetic composition that is favourable for the farmed environment but probably less favourable for conditions in the wild. The genetic material of farmed salmon also has less variation than that of wild salmon, but because the breeding material comes from several Norwegian rivers, the farmed salmon do not have one single gene that is not present in wild salmon.

Many escaped farmed fish die before they can swim up river. Conditions in the river may also affect the potential of fish to spread their genes. Farmed salmon produce fewer viable offspring than wild salmon because they are not adapted to the environment. Only the fittest survive.

Gene flow

"In this project we plan to map the flow of genes over time. We want to find out whether the genetic variation of wild salmon is reduced when farmed salmon interbreed with the wild salmon stock," says Sten Karlsson. Large genetic variation is preferable, as it enables the salmon to adapt to future changes in the environment.

In this study the researchers will use genetic material from old wild salmon strains and breeding populations. A software program has also been developed for identification of functional genetic markers as opposed to genetic markers that do not affect the phenotypic properties.

The Research Council of Norway is funding the project, and Nofima is cooperating with the Norwegian Institute for Nature Research (NINA), CIGENE and two research groups in Ireland. The project will conclude in 2010.

May 2009

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