Disruptive communication: stealth signaling in the toadfish.

Male oyster toadfish, Opsanus tau, produce long duration (250 to 650 ms) sexual advertisement calls or 'boatwhistles' during the breeding season. When males are in close proximity, the fishes alternate the production of boatwhistles with other males to avoid call overlap. However, males can also produce a number of different sounds, including a single, short duration pulse or 'grunt' (~100 ms). The vocalizations of competing males were recorded in situ with multiple hydrophones to examine intraspecific interactions. These short grunts were emitted almost exclusively during the boatwhistle of a conspecific male. The fundamental frequency (or pulse repetition rate) of the boatwhistles were modified by this disruptive grunt, 'jamming' the signal and decreasing its frequency. The disruptive grunt specifically targeted the second stage or tonal portion of the boatwhistle, believed to be the primary acoustic attractant for females, and its brevity and precision may allow its emitter to remain undetectable. While the acoustic repertoire of teleost fishes may be less diverse compared with terrestrial species, the disruptive grunts indicate fish have the capacity for complex acoustic interactions.