Fig. 5. Na⁺/K⁺-ATPase (green in A,C,E,G,I,K) and Na⁺/K⁺/2Cl^– cotransporter (red in B,D,F,H,J,L) immunoreactivity in the gills of lake trout (A–D), brook trout (E–H) and Atlantic salmon (I–L) kept in 0 p.p.t. (freshwater; A,B,E,F,I,J) and those transferred gradually and kept in 30 p.p.t. (seawater) for 3 weeks (C,D,G,H,K,L). The nuclei were counterstained with DAPI (blue). The primary filaments are horizontal, and about three secondary lamellae are seen perpendicular to each filament. Scale bar, 20 µm.