Arguments have been made for and against the traditional swim bladder model as a primary component of fish vocalization. This paper presents arguments for decoupled forced and resonant responses being extractable features within a variable air volume. As such, a mechanical analog is used to show how envelope modulation may be used by some species to identify air volume and consequently size in conspecifics. These arguments consider how an arbitrary fish may apply a genetic strategy of forcing vocalization through slow, fast, or both slow and fast sonic musculature while amplitude modulating via swim bladder. The classic resonant bubble model is revised to account for a hypothetical carrier signal resonance associated with static or varying volume. In the absence of live specimens, a test is conducted in different cylindrical structures with equally sized air volumes. First, a proposed method for extraction of swim bladder volume features through blind amplitude demodulated signals in the time and frequency domain is applied. Second, a proposed method for extraction of swim bladder volume features through cyclostationary analysis of the cross-spectral coherent spectra of the modulated and demodulated signal is applied. Both methods take average frequency content as derived by the prescribed signal processing techniques as the input to the correlator functions used to identify air volumes. Vocalizations of
© 2018. Published by The Company of Biologists Ltd.
Competing interestsThe authors declare no competing or financial interests.
