Design of the experiment. A: Two study groups of Atlantic salmon were SL infected fish with approximately 75 copepodids per fish. On days 3, 22 and 33 tissue samples were collected from the control and infected test groups; time-points corresponded to copepodids (3 dpi), chalimus III/IV (22 dpi) and preadult stages (33 dpi). B: Due to the small size of SL at the copepodid stage, it was not possible to reliably locate them on fish at the sample taken 3 dpi. Consequently, SL damaged skin was only sampled 22 dpi and 33 dpi. Salmon lice tend to aggregate around fins. Therefore, the area behind the dorsal fin was chosen in order to sample damaged skin. Because attached lice were never found along the lateral line, samples of intact skin of infected fish were taken from the area below the dorsal fin at the intersection with the lateral line. SI – intact skin; SD – damaged skin; SPL – spleen; HK – head kidney; L – liver; dpi – days post infection.