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Structurally diverse sensory regions occur in the otolith organs of the goldfish inner ear. Scanning electron microscopy reveals regional distinctions based on three criteria. (1) Hair cells have different sizes of apical bundles, based on thickness. In all three maculae, two central regions have hair cells with bundles significantly thicker than those in surrounding regions. (2) Hair cell population density varies, with regional aggregations present. The central regions with thick bundles have two to three times the density of surrounding regions with thin bundles, and contain 40-80% of the total hair cell number in each macula. (3) Hair cell orientation maps show that each macula has two oppositely oriented cell populations that can be separated completely, not by a zone of interspersion, but apparently by a single unbroken line. The lagena is like the utricle in having hair cells with the kinocilium on the side of the cell toward the opposition line, but in the saccule the kinocilia face away from the line, and the small macula neglecta consists of two completely separate, oppositely oriented patches. The opposition line does not divide each macula simply down its midline; instead, the line divides the regions with thich bundles into nearly equal opposing areas, except for a remarkably abrupt large loop in the line in the anterior part of the saccule. The regional structural diversity in these organs may relate to localized functional diversity of responses to tilt, vibration and sound.

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Scanning electron microscopy and standard histological techniques were used to describe the basic anatomy and postembryonic growth of the lateral line system of Cottus bairdi. The gross anatomy and distribution of lateral line neuromasts in canals and superficially on the skin are similar to what has been reported for many primitive actinopterygian fishes. Both canal and superficial neuromasts showed postembryonic growth in the number of hair cells and size of neuromasts, but canal neuromasts grew more elongate whereas superficial neuromast grew symmetrically. Neuromasts in the mandibular canal grew significantly faster than any other neuromasts and superficial neuromasts on the head showed the least amount of growth. Differential growth of the sculpin lateral line system may be related to the feeding behavior of the animal and to differences in the ambient levels of water noise to which larval and adult fish are exposed.

The sensory end organs of the inner ear of the lungfish, Protopterus, were examined using scanning and transmission electron microscopy. The utricle has a structure and hair cell orientation pattern that are typical for vertebrates, although the hair cells are unusually large. There are the typical three semicircular canals extending from the utricle, with the typical hair cell orientations, but the lateral canal sensory crista looks like the "hemicrista" of some amphibians and amniotes, lacking a saddle-shaped flare on one wall of the ampulla. Unlike most vertebrates that have the saccule and lagena as two separate pouches ventral to the utricle, the lungfish has a single large ventral pouch that contains a single large pasty otoconial mass. This mass covers two hair cell patches, each like a striola with prominent hair cell ciliary bundles, that are presumed to represent saccular and lagenar maculae. However, these two major sensory patches are not completely separate maculae because they lie within a less densely populated field of smaller hair cells, which forms an extrastriolar region that surrounds and fills the region between the two striolae of higher hair cell density. The more caudal lagenar striola is a vertically elongated stripe with hair cell orientation vectors facing antiparallel on either side of a midline drawn vertically along the macula, resembling the macula lagena of some bony fishes but not of tetrapods. The more rostral saccular striola is a curving band with hair cell orientation vectors facing away from its midline, but because this macula curves in three dimensions, the vectors at the rostral end of this striola are oriented mediolaterally, whereas the vectors on the caudal half of this striola are oriented dorsoventrally. The presence of a macula neglecta was confirmed near the posterior canal as a tiny single patch of a few dozen hair cells with all the cell orientations directed caudally. The ciliary bundles on the cells in the striolar-like regions of all of three otolithic organs average over 80 cilia, a number far greater than for any other fish studied to date. The features of the single sacculolagenar pouch with separate striolar-like regions, the cellular orientation in the otolith organs, and the large cells and ciliary bundles in Protopterus also were observed in specimens of the other extant lungfish genera, Lepidosiren and Neoceratodus.

The inner ears of a few fishes in the teleost superorder Ostariophysi are structurally unlike those of most other teleosts. Scanning electron microscopy was used to determine if other ostariophysans share these unusual features. Examined were the families Cyprinidae, Characidae, and Gymnotidae (all of the series Otophysi), and Chanidae (of the sister series Anotophysi), representing the four major ostariophysan lineages, the auditory organs of which have not yet been well described. Among the Otophysi, the saccular and lagenar otolith organs are similar to those reported for other ostariophysans. The lagena is generally the larger of the two organs. The saccular sensory epithelium (macula) contains long ciliary bundles on the sensory hair cells in the caudal region, and short bundles in the rostral region. The saccule and the lagena each have hair cells organized into two groups having opposing directional orientations. In contrast, Chanos, the anotophysan, has a saccular otolith larger than the lagenar otolith, and ciliary bundles that are more uniform in size over most of its saccular macula. Most strikingly, its saccular macula has hair cells organized into groups oriented in four directions instead of two, in a pattern very similar to that in many nonostariophysan teleosts. We suggest that the bi-directional pattern seen consistently in the Otophysi is a derived development related to particular auditory capabilities of these species.