AbstractTrichopsis vittatusemits high amplitude sounds during agonistic encounters with conspecifics. The sound producing organ is derived from the structural components of the pectoral fins.The study involved muting a sample of subjects by removing two pectoral fin tendons without any further restriction in movements and behaviour. Mute and unaltered males were then placed together in pairs and the following agonistic behavioural elements were determined: attacks, lateral displays, sound production and frontal displays.Soniferous males had a higher probability of winning contests when size differences were small. In pairs with big size ratios, the larger males were more often successful. Besides visual and acoustical signals, lateral line stimuli seem to play no role in threatening displays.These results demonstrate that vocalization during agonistic encounters is important for becoming dominant in specific circumstances. Because of correlation between main frequencies and size, sound emission might be a very effective method of assessing the physical strength of an opponent.
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