Studies will take advantage of recently developed oligonucleotide microarray platforms for salmon (Nofima Marin) and lice (University of Bergen) and samples obtained from the ongoing NRC funded project 1900486/S40. Multiple gene expression profiling will compare lice collected from fish with high and low lice resistance. Results will elucidate molecular factors that determine infectivity of lice and thus promote development of measures against the parasite.