Comparative structure of the fish ear

Abstract

Comparative investigations of over 20 species of fish show that there is significant interspecific variation in several aspect of the anatomy and ultrastructure of the inner ear. Variation is particularly extensive in the sacculus and lagena, the two regions of the ear thought to be involved in sound detection. The most striking interspecific variation is in the orientation patterns of the sensory hair cells, as determined with the SEM. In some species the hair cells are found in one of two groups, with all cells in each group oriented in the same direction. In other species there are four orientation groups. The relationship between the orientation groups appears to be species specific. On the gross anatomical level variation includes the relative orientation between the two otolithic organs and the connections, if any, between the sacculus and the cranial cavity. There is also considerable variation in the relationship between the single otolith and the sensory maculas. In some species the otolith “covers” the whole macula while in other species only a small portion of the macula is in contact with the otolith. Variation found in the ear may have functional and taxonomic significance particularly with regard to comparative sound detection mechanisms. [Supported by NIH and Deafness Research Foundation.]