Within labyrinth fishes (Anabantoidei), croaking gouramis Trichopsis vittatus and pygmy gouramis T. pumila vocalize regularly during agonistic interactions. These vocalizations are broad-band pulsed sounds with high- pitched dominant frequencies (1-2.5 kHz), which contrast with the generally low-frequency hearing abilities of perciform fishes. Utilizing a recently developed auditory brainstem response recording technique, the auditory sensitivity was measured and compared to sound characteristics. The dominant frequencies of sounds were 1-2 kHz and 1.5-2.5 kHz for croaking and pygmy gouramis, respectively. Maximum low-frequency sensitivity for both species was 0.1-0.2 kHz. Maximum high-frequency sensitivity occurred between (3.8 and 2 kHz for croaking gouramis, which closely matched the best frequency of hearing. However, the best hearing frequency of pygmy gouramis was below 1.5 kHz, which indicated a mismatch between the two parameters. The correlation between sound production and perception in these fishes is likely to be facilitated by the suprabranchial airbreathing cavity, which lies close to the hearing and sonic organs and enhances both sound perception and emission at its resonant frequency. Additional examination of Macropodus opercularis, Trichogaster trichopterus and Colisa lalia revealed that all five gourami species could perceive sounds up to 5 kHz. The high-frequency hearing abilities of labyrinth fishes qualifies this group as hearing specialists.
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