Breeding Salmon for Resistance to Sea Lice

Lucy Towers
20 August 2013, at 1:00am

NORWAY - There is considerable genetic variation in the resistance to sea lice in salmon and, with targeted breeding, it is possible to breed salmon with properties that do not favor sea lice.

Today there are usually three methods used to combat sea lice: treatment with drugs, using other fish and vaccination.

All these methods however, offer problems. Delousing with drugs is most prevalent, but the problem is that lice become resistant.

Method two, using species such as wrasse to eat the lice, is challenged through the limited availability of wild wrasse. Commercial production of wrasse is therefore a priority.

The third method is a vaccine against sea lice. This work is still at the development stage.

Breeding can solve the problem

"Breeding is a fourth method. Nofima's test results indicate that this may be the way to go to solve the louse problem. Salmon lice resistance can be increased by using fish from families who are at little risk of being attacked by lice larvae as broodstock for new generations of farmed salmon," says senior scientist and project manager Bjarne Gjerde, Nofima.

He explains that some salmon families are less likely to get lice, just as some people are less susceptible to mosquito bites.

Theoretical calculations show that through the selection only for increased resistance to sea lice, we can expect an increase of 24 per cent per generation, and the cumulative effect of 75 per cent over five generations.

In practice, the progress will be less than this because selection must also be done for other features.

Breeding can be an important measure to solve the lice problem but it will take some salmon generations before the effect becomes noticeable.

"I think we would have been better served if the state either requires all breeding companies to make a selection for increased resistance to sea lice or the granting of a subsidy to the breeding companies that choose to do so on their own initiative," says Mr Gjerde.

The project towards breeding for increased resistance to sea lice in salmon is funded by the Norwegian Research Council, Fisheries and Aquaculture Industry Research Fund and SalmoBreed AS.