The olfactory epithelium of an adult zebrafish. (a) Photomicrographs of the semithin section showing the kappe cells (purple arrows), one-ciliated ON (yellow arrows), multi-ciliated ON (orange arrows), microvillous ON (green arrows), and crypt neurons (red arrow) surrounded by special supporting cells (blue arrowheads). Toluidine blue; magnification, 20×. (b) A zebrafish epithelium olfactory neuron’s graphic representation modified using the transmission electron microscopy micrograph from our previous study [10]. Abbreviations: k, kappe cells; sc, supporting cells; m-ci, multi-ciliated ON; n, nucleus; o-ci, one-ciliated ON, ci, cilium; mv, microvillous ON; mi, microvillus; cn, crypt neurons, with several cilia within the crypt (asterisk), special supporting cells (sc), and basal lamina (bl).