The cellular and genetic response to sea lice infection: How might we use this knowledge to improve Atlantic salmon host-resistance to sea lice?

Selective breeding for Atlantic salmon host-resistance has been looked upon as a
promising and cost-effective solution for reducing the lice problem. The trait under
selection has been the number of sessile lice per fish. However, recent work has shown
that the potential for group-level protection is lower than originally expected casting
doubt on the reliance on lice count as an indicator trait. Lice counts are heavily influenced
by the initial rate of copepodid attachment success and would not be very sensitive to
subtle underlying differences in the immune response of the fish against the lice. So, if our
aim is to improve the immune response of Atlantic salmon against sea lice, we will need
cost effective indicator phenotypes that reflect the strength of the underlying genetic
variation in the response against the lice. This is where the knowledge we have gained
about the effective immune responses mounted by other Pacific salmonid species in the
FHF funded CrispResist project (Harnessing cross-species variation in sea lice resistance
901631) could be applied. Here we show how the genetic and cellular response after
sea lice infection differs between more susceptible and more resistant salmon species,
and how this might allow us to test and select Atlantic salmon for a Pacific-like immune
response to directly reduce the lice burden and reduce the need for delousing.