Hopp til hovedteksten
Kevin Glover
Kevin Glover is the project manager of the study, which has found that salmon lice are capable of developing tolerance to both fresh and warm water treatment.
Photo: Erlend Astad Lorentzen / Institute of Marine Research
Print friendly version

Salmon lice capable of developing tolerance to fresh and warm water treatment

Genetic variations mean that different families of salmon lice have different tolerances to freshwater and warm water. Both treatments are used to delouse farmed fish. The findings suggest that salmon lice could eventually develop higher tolerance to the treatments, rendering them less effective.

The discovery was revealed in an article recently published in the journal Evolutionary Applications by scientists from the Institute of Marine Research and the Sea Lice Research Centre at the University of Bergen.

 “We’ve conducted two experiments to look at how different families of salmon lice tolerate treatment in freshwater and warm water. The lice should in principle not tolerate either, which is why these treatments have become prevalent delousing methods in the aquaculture industry,” says project manager Kevin Glover.

Diminishing effect of treatment in the long term

After experimenting on multiple salmon lice families, the results were compared.

“We noted clear differences in tolerance levels in the different families, and the louse as a species is therefore capable of developing increased tolerance to treatment with both freshwater and warm water,” Glover says.
Tolerance levels increase as the lice that best tolerate the treatment survive. These lice will eventually create their own offspring, and there is a big chance that the offspring will be born with higher tolerance to the treatment that their parents survived. In the long term this could mean that the salmon lice population will develop increased tolerance to freshwater (low salinity) and potentially also warm water. This has already happened when it comes to certain medicines.
“It’s important to stress that our findings do not mean that salmon lice are becoming resistant to treatment with freshwater and warm water, but they are highly likely to tolerate it better, rendering the treatments less effective in the long term,” says Sissel Rogne, director of the Institute of Marine Research.

Still efficient delousing methods

“This is fascinating work. As yet, we are the only institute to have bred families of salmon lice for such experiments, and we are the first to demonstrate that there are genetic variations in the extent to which salmon lice tolerate different temperatures and salinity levels,” Rogne says.
She stresses the importance of not exaggerating the significance of the findings.
“Environmental treatment of salmon lice remains an efficient delousing method, but it’s important to keep monitoring the effects of these treatments.”

Facts about sea lice

Latin name: Lepeophtheirus salmonis
Distribution: occur naturally in Norwegian waters. Their numbers have risen significantly in parallel with the growth of the aquaculture industry.
Biology: sea lice are parasites with eight life stages, three of which are free-swimming, two of which are stationary and three of which are mobile. They attach themselves to salmon in the third life stage.
Size: adult female: 12 mm (approx. 29 mm including egg strings); adult male: 6 mm.
Diet: the skin and blood of salmonids. The lice only start feeding when they have attached themselves to a host fish (stationary and mobile stages).
Reproduction: all year round, but reproduce increasingly quickly as temperatures rise in spring.
Dispersal: free-swimming stages spread on currents in fjords and coastal waters.
Treatment: biological methods (wrasse) or chemicals (medication).

Sea lice