Figure 2

Cellular response of Coho epithelium to salmon lice. Representative histopathology of Okis fin and gills during the host response 4–7 dpi revealed several populations of cells involved in the epithelial response to Lsal (a–g). Whereas control fin was characterized by populations of mucocytes (a, b), infected fin was characterized by thickened epithelium and mucocyte hypoplasia (c–d). Sacciform cells (red arrowheads) were present in control and infected fin and were typically associated with the apical surface, however, they were more abundant at the louse attachment sites (red circles, g). Accumulation of melanomacrophages was evident in infected fin (c, e; star), and this was often associated with leukocytes as observed in fin and gill (e–f; black arrows). Epithelial hyperplasia was evident by 4 dpi (d, red star), and this response included significant presence of lymphocytes (f, g), and granulomatous inflammation (g; star).