Abstract
In addition to briefly reviewing sound-producing mechanisms, this chapter focuses on an under-appreciated evolutionary process, exaptation, which could aid in understanding the independent origins and high diversity of sound-producing mechanisms in fishes. Existing anatomical structures first used in non-voluntary sound production provide advantages that result in further selection and refinement of sophisticated sonic organs. Moreover, comparisons of the relationships between fish size and spectral features in multiple not phylogenetically related species highlight two acoustic patterns. In species using superfast muscles, the slope of the relationship between fish size and sound frequency is weak (1°–5°) so that emitter size is unlikely inferred from call frequency. In other species that stridulate or use bones or tendons to stimulate the swimbladder, the high slopes (25°–80°) indicate major differences in the call frequencies within a species. These signals likely convey important information (size and potential fitness of the emitter) to conspecific receivers.