Counting salmon lice at Nofima. Photo: Bjarne Gjerde/Nofima

Project Year 2013

Salmon that don’t tempt lice

Purposeful selective breeding makes it possible to develop a salmon with increased resistance to lice.

There are currently two methods to combat salmon lice: delousing with medications and biological delousing.
However, both methods offer problems. Delousing with medications is widespread, but the lice develop resistance
to this. The challenge with biological delousing – using other species wrasse to eat the lice – is a limited
supply of wild wrasse. Commercial production of wrasse is therefore a priority area. A vaccine against lice is at the
development stage.

SELECTIVE BREEDING CAN SOLVE THE PROBLEM: “Selective breeding is another method. Our trial results indicate that this may be the way to solve the problems with lice. Some salmon families are less likely to get lice, just as some people are less likely to be bitten by mosquitoes,” says Senior Scientist Bjarne Gjerde.

Consequently, the salmon’s resistance to lice may be increased by using fish from families with high resistance
to lice as broodstock for new generations of farmed salmon.

Theoretical calculations show that by selecting only for increased resistance to lice, we can expect progress
of 24 % per generation, and the cumulative effect of 75 % over five generations. In practice, the progress will be
less than this as selections must also be performed for other traits.

NEED LONG-TERM APPROACH: Selective breeding can be an important measure to combat the problems with
salmon lice, but it will take a few salmon generations before the effect is noticeable for the individual farmer.
Breeding companies that select for increased resistance to lice will currently have higher costs than those
that only select for traits that provide direct returns.

“I believe we will be better served if the State either instructs all breeding companies to make a selection
for increased resistance to lice or subsidises those that choose to do so on their own initiative,” concludes

The Research Council of Norway, the Norwegian Seafood Research Fund and SalmoBreed

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