Comparison of the inner ear ultrastructure between teleost fishes using different channels for communication

The anatomy and ultrastructure of the inner ear of three species of gouramis which differ widely in acoustic behavior were studied using scanning electron microscopy. Of the three species. Trichopsis possess a pectoral sound-producing mechanism while Macropodus and Betta lack sonic organs. The general structure of the inner ear and the shapes of the sensory epithelia are very similar, although they do differ on the posterior part of the saccular macula which is more S-shaped in Trichopsis and Macropodus than in Betta. The maculae on the three species do not differ either in ciliary bundle type (cells with long kinocilia on the periphery of the maculae and cells with short kinocilia in the central region) or in hair cell orientation pattern. Quantitative measurements of hair cell densities and the size of the sensory epithelia of the saccule did not show significant differences between species. Data presented correlate with physiological results from other investigators showing similar auditory sensitivity in Trichopsis and Macropodus. The similarity in structure and function of the inner ears of gouramis on one hand, and the occurrence of sound-generating organs in just one genus, suggests that hearing evolved prior to vocalization and thus acoustic communication in this taxon.