The fine structure of the sacculus and lagena of a teleost fish.

The ultrastructure of the sensory epithelia in the auditory regions of the ear, the sacculus and lagena, were investigated in the blue gourami, Trichogaster trichopterus, using transmission and scanning electron microscopy. The sensory epithelium consists of sensory hair cells surrounded by supporting cells, both of which are quite similar to comparable cells found in other fishes. The apical surface of each sensory cell contains a ciliary bundle which varies in length in different epithelial regions. Tight junctions and one or more levels of desmosomes are located between supporting cells, and between sensory and supporting cells, just below the apical cell membrane. Peripheral to the actual sensory epithelium is a region of epithelial cells that resemble the supporting cells on the sensory epithelium itself. However, interspersed among these cells are other cells containing large numbers of mitochondria, extensive smooth endoplasmic reticulum, and large vacuoles. Investigations of the orientation patterns of the ciliary bundles on the sensory hair cells demonstrate that the lagena is typical of other Perciform fishes while the position of two of the four orientation groups normally found in the Perciform sacculus are quite different in Trichogaster from that found in other species. Comparisons of the ultrastructure of the sensory and supporting epithelia of Trichogaster and other fishes shows that, with the exception of the mitochondria-filled cells, there are no apparent significant interspecific differences with regard to ultrastructure of the sensory and supporting cells themselves, although there are differences in hair cell orientation patterns among the same fish groups.