The functional organization of the fish olfactory system.

Recent developments in the functional anatomy and physiology of the fish olfactory system reveal three parallel pathways from the sensory epithelium, via the olfactory bulb to the telencephalon. There are three morphological types of sensory neurones spread in a seemingly overlapping arrangement in the olfactory epithelium. The axons of each type of sensory neurones converge to a specific region of the olfactory bulb and connect to separate sets of relay neurones. The axons of these relay neurones leave in three bundles to the telencephalon. Each bundle conveys specific information that elicits sets of characteristic behaviour in response to odours involved in essential life processes in the fish. One pathway is tuned to social cues, another to sex pheromones, and the third to food odours.