Central projections of octavolateralis nerves in the brain of a soniferous damselfish (Abudefduf abdominalis).

Sounds and hydrodynamic stimuli are important cues detected by the octavolateralis system in fishes. The central organization of auditory, mechanosensory, and vestibular projections is known for only a few phylogenetically diverse fishes, and less is known about projections in derived perciforms that use sounds for acoustic communication. We used neuronal labeling to provide a detailed analysis of octavolateralis endorgan projections in a soniferous perciform that does not have accessory morphological structures to enhance hearing. Octavolateralis nerves terminate ipsilaterally within seven medullary octaval nuclei: caudal (CON) and medial (MON) octavolateralis, anterior (AON), descending (DON), magnocellular (MgON), tangential (TON), and posterior (PON) octaval nuclei, and the eminentia granularis (EG). Anterior and posterior lateral line nerves project to the CON and MON, with dense projections to the EG. Semicircular canal nerves project primarily to ventral regions including the TON, ventral DON, intermediate DON (DONi), and MgON. Otolithic, semicircular canal, and anterior lateral line nerves all project to the MgON, which may serve a sensorimotor integration function. The DONi receives primarily segregated projections from all otolithic and semicircular canal nerves, whereas the ventral DON and TON receive principally utricular and semicircular canal afferents. The AON receives dense lateral and ventral projections from the saccule and utricle, and medial and dorsal projections from the lagena. These projection patterns are similar to those reported for non-sonic perciforms, and indicate the absence of neuroanatomical modifications in first-order octavolateralis nuclei in species that use acoustic communication. Thus patterns of central projections may be conserved among vocal and non-vocal perciforms.