Abstract
ABSTRACTArguments 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 Epinephelus guttatus, or more commonly known as the red hind grouper, are used as test signals.
Highlights
The swim bladder model for resonance as defined in Ladich (2015) is understood to be one of the most widely accepted approaches to characterizing vocalization from fish who apply muscle contractions across the swim bladder to generate sound
This paper presents a methodology for isolating envelope modulation characteristics associated with resonance of air cavities in water being impulsively excited by an external source
As a means of controlling the signal output, an identical test reference vocalization with no variation in power was played through four varying air volumes, and each air volume was correctly assessed by both methods considered
Summary
The swim bladder model for resonance as defined in Ladich (2015) is understood to be one of the most widely accepted approaches to characterizing vocalization from fish who apply muscle contractions across the swim bladder to generate sound. Evidence has been found to support that some fish are at least sensitive to the effects of envelope modulation (McKibben and Bass, 2001). Researchers are presenting challenges to the conventional resonating bubble model (Fine, 2012) in terms of understanding how fish apply its use. When considering the possibility of a time and envelope modulation dependent strategy in terms of the findings in McKibben and Bass (2001), it becomes of interest to consider possible biological rationale for developing such proclivities
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