Fig. 1. Immunofluorescence staining of (A) Na⁺,K⁺-ATPase (green) and (B) occludin (red) in longitudinal sections of a goldfish gill filament. Nuclei are stained with DAPI (blue) in A and F. C is a merged image of A and B. In A, Na⁺,K⁺-ATPase immunolocalizes to select cells within the interlamellar (IL) region of the primary filament and at the base of secondary gill lamellae. In B, discontinuous occludin immunostaining is concentrated along the edges of secondary gill lamellae (white arrow), including medial parts of lamellae that are embedded within the body of the primary filament, and is associated with cells that also stain for Na⁺,K⁺-ATPase (white arrowhead). Occludin immunostaining is also prominent in parts of the IL region that line the lateral walls of the central venous sinus (CVS). D and E show, at higher magnification, areas from C that are indicated by the white arrowhead and white arrow, respectively. Control sections probed with secondary antibody only show DAPI fluorescence (F). Scale bars in A, B, C and F are 20 µm. Scale bars in D and E are 5 µm.