Fig. 1. Neuroepithelial cells and associated innervation in the gills of adult zebrafish. (A) Confocal image of two adjacent gill filaments (f) with respiratory lamellae (lam). Neuroepithelial cells (NECs, green) were serotonin (5-HT)-immunoreactive (IR) and located in the filaments (i.e. O₂-sensitive NECs) and lamellae (arrows). Both NEC populations were innervated by zn-12-IR nerve fibres (red; arrowheads) that emanated from nerve bundles. Scale bar, 50 µm. (B) Serotonin (5-HT)-immunoreactive (IR) NECs (green; arrows) of the gill arch (ga). NECs of the gill arch were organized along a zn-12-IR (red) nerve bundle (nb) and were innervated by zn-12-IR nerve fibres (arrowheads). Also visible are 5-HT-IR NECs of the respiratory lamellae (lam) near proximal regions of the gill filaments (f), and 5-HT-IR Merkel-like basal cells of the gill rakers (gr). Scale bar, 50 µm.