Helge Tveiten has spent ten years developing the method that allows breeders to produce sterile salmon without genetic manipulation. Photo: Ole Åsheim ©Nofima

Project Year 2017

Sterilisation breakthrough for farmed salmon

 Production biology  

After ten years of research, Nofima has finally cracked the code on how fish farmers can produce sterile salmon – without genetic manipulation.

A key protein is modified in the egg stage, so the salmon do not develop reproductive cells.

There are currently over 2,000 sterile salmon swimming round at the aquaculture station in Tromsø. Senior scientist Helge Tveiten is very pleased, since all the signs indicate that they are just as happy as any other salmon. Scientists have found a method that only affects the fish’s ability to reproduce, and nothing else. The biggest fish here are now one year old and weigh around 300 grams.

“The salmon we have bred don’t develop reproductive cells and will never mature sexually. The females develop a very small roe pouch, but eggs don’t form. Male fish develop seemingly normal sexual organs, but they don’t have sperm cells,” Tveiten explains.

Based on the studies carried out so far, the sterile fish have the same appearance and properties as fertile farmed salmon.

Faith in the idea

Tveiten encountered some scepticism in other research circles when he presented this sterilisation method, and Nofima has therefore used substantial own funds in this project.

“In purely biological terms, I knew early on that this method was viable. Research on zebra fish had identified a small number of genes that are decisive for the development of reproductive cells. The removal of one or more of these gene products resulted in a fish without reproductive cells, but which otherwise developed normally. There was no reason a similar approach could not be used on salmon. In practice, we don’t touch the genes; rather we modify a protein required for the fish to develop reproductive cells,” the senior scientist explains.

With time, several partners have recognised that this sterilisation method may resolve many of the challenges facing the aquaculture industry.

Environmental protection and animal welfare

Tveiten’s important findings are excellent news for many circles. There are numerous good reasons for producing sterile farmed fish, including environmental protection and animal welfare.

If farmed salmon are sterile, escapees will not interbreed with wild salmon, impairing the wild salmon population – a scenario feared by many today. Additionally, fish farmers would prefer to prevent salmon from maturing, as they become significantly more susceptible to disease and have greater problems maintaining the water–salt balance in the sea.

“The quality of the fillets also deteriorates when salmon mature, resulting in a lower value product,” the scientist adds.

Few alternatives

Tveiten and co.’s work led to the establishment of the research project SalmoSterile, the goal of which is to find a simple, safe way to sterilise farmed fish. Now that the method is here, all that remains is to rationalise it, so that the industry can start processing the eggs on a large scale.

Today, salmon are sterilised using triploidisation, where the fish are given a second set of chromosomes. Triploid salmon, however, are inferior to normal fertile salmon, and this method is not used very widely. It is therefore essential, according to Tveiten, to develop better, more targeted sterilisation methods.

“We will have to monitor these fish over time, but there is nothing to indicate that they will mature or have a migratory urge to spawn. Of course, thorough investigations must be conducted to find out whether escaped sterile salmon will move up rivers. This will require more research, but as it stands, such a scenario is very unlikely,” Tveiten believes.

The next phase is to develop the method for the industry, in collaboration with industrial actors and the salmon industry.


The Institute of Marine Research and industrial partners

The Research Counsil of Norway (NFR), and the Fiskery and the Aquaculture Industry Research Fund

More useful research results