Trial outline.

Three groups of Atlantic salmon from Penobscot river strain and St John river strain (six replicate tanks per treatment): sea lice infestation plus ISAv, sea lice infestations no ISAv, and no sea lice infestation no ISAv controls. Fish were bath infested with L. salmonis followed by an ISAv cohabitation infection 18 days post-lice exposure. Twenty-four fish were euthanized per treatment group (n = 12 Penobscot–derived and 12 St John–derived fish, each made up of three distinct families) at days -1, 3, 16, and 37 d.p.e., and the following parameters sampled number of lice per fish, head kidney for immune gene expression and ISAv QRT-PCR kidney, spleen and heart for cell culture. Forty-five Atlantic salmon per treatment group were also monitored until no mortalities had occurred in any group for 7 days. At 51 d.p.e. all survivor fish were sampled as detailed below.