KAATZ, I.M.: Structurally divergent sound producing mechanisms in a clade of arioid catfishes function in different behavioral contexts

Of the over 400 teleost fish families, 23% are known to have evolved two or more structurally and acoustically different sound producing mechanisms (SPMs). What is the functional significance of these independently derived SPMs? Structurally different SPMs are known to produce acoustically different sounds (Demski, Gerald and Popper 1973). Species with multiple mechanisms provide the opportunity to study how signal design relates to specific behavioral functions. Swimbladder and stridulation acoustic mechanisms differ in frequency range, temporal pattern and amplitude. I test the hypothesis that these two SPMs function in different behavioral contexts. Twelve species of catfishs in the arioid superfamily were maintained in monospecific groups in aquaria in a sound proof room. The number of swimbladder and stridulation sounds produced in intraspecific contexts (sounds hypothesized as conspecific targeted signals) were monitored with a hydrophone and recorded on VHS. The mean number of focal samples per species was 60. The mean number of sounds observed per species was 176. Sounds produced by the same individuals in the disturbance context (sounds hypothesized as predator targeted signals) were recorded in the field (recorded underwater while hand restrained). The mean number of sounds produced per species was 468. In intraspecific contexts swimbladder sounds were more abundant in ten species (69-100% of total sounds per species) and uncommon in two species (20-30%). In the disturbance context stridulation sounds were more common in all except four species. The relative use of swimbladder and stridulation SPMs in different behavioral contexts was species specific.