The olfactory nerve in zebrafish is composed of olfactory sensory neuron (OSNs) axons. There are three types of olfactory sensory neuron in fish, cilliated cells,microvillus sensory neruons and crypt cells (Kermen et al., 2013). Chemical odorants in the water are detected by olfactory receptors on the OSNs who have their soma located inside the olfactory epithelium(the zebrafish nose). OSN axons innervate the olfactory bulb where they connect with the dendrites of mitral cells and other olfactory bulb neurons at structures called glomeruli.

Frontal view of a Tg(-10lhx2a:GAP-EYFP) embryo. This transgenic line labels the olfactory epithelium(the nose) and the olfactory nerve. Olfactory sensory nerve (OSNs) axons innervate the olfactory bulb where they connect with mitral cells at structures called glomeruli. This transgenic line also labels some mitral cells in the olfactory bulb that send projections to Dp (the olfactory area of the pallium and also to the right habenula.

Frontal view of a Tg(-10lhx2a:GAP-EYFP) embryo. This transgenic line labels the olfactory epithelium(the nose) and the olfactory nerve. Olfactory sensory nerve (OSNs) axons innervate the olfactory bulb where they connect with mitral cells at structures called glomeruli. This transgenic line also labels some mitral cells in the olfactory bulb that send projections to Dp (the olfactory area of the pallium and also to the right habenula.

Key Publications

Miyasaka, N., Morimoto, K., Tsubokawa, T., Higashijima, S., Okamoto, H., and Yoshihara, Y. (2009)
From the olfactory bulb to higher brain centers: genetic visualization of secondary olfactory pathways in zebrafish.
The Journal of neuroscience. 29(15):4756-4767.

Miyasaka, N., Arganda-Carreras, I., Wakisaka, N., Masuda, M., Sümbül, U., Seung, H.S., Yoshihara, Y. (2014) Olfactory projectome in the zebrafish forebrain revealed by genetic single-neuron labelling.
Nature communications. 5:3639.

Dreosti, E., Vendrell Llopis, N., Carl, M., Yaksi, E., and Wilson, S.W. (2014) Left-right asymmetry is required for the habenulae to respond to both visual and olfactory stimuli.
Current biology : CB. 24(4):440-445.

Byrd CA, Brunjes PC.
Organization of the olfactory system in the adult zebrafish: histological, immunohistochemical, and quantitative analysis.
J Comp Neurol. 1995 Jul 24;358(2):247-59.

Florence Kermen, Luis M. Franco, Cameron Wyatt, and Emre Yaksi
Neural circuits mediating olfactory-driven behavior in fish
Front Neural Circuits. 2013; 7: 62. doi: 10.3389/fncir.2013.00062