The Toadfish is probably more well known for its unique swim bladder than its ability to make noises but a recent study by researchers at Cornell University may change that as toadfish may be sending complex information in the noises they make. These grunts, groans and hoots just might be communicating everything from pickup lines for potential mates to warning for coming too close to their home.
Although hard-to-discern sounds adding an extra layer of vocal information have been observed in birds, amphibians and mammals,these subtle harmonics and dissonances, called nonlinearities, have not been observed in fish.
“Fish rarely come to mind when we talk about animal sounds. It’s always seen as sort of boring, simplistic communication,” said biologist Aaron Rice of Cornell University, who led a study of three-spined toadfish vocalizations in Proceedings of the Royal Society B May 11. But with the right kind of analysis, “complex underlying structures emerge in images of these sounds. We think they’re communicating detailed information.”
But before we dive into that, we need a quick background on their swim bladders. Toadfish are bottom dwellers with twin-chamber swim bladders. Each bladder is independently controlled with muscle twitches up to 200 times a second — making it the fasted moving muscle in the entire animal kingdom. By manipulating their swim bladders, toadfish are able to make noises which we previously just dismissed as simple communications.
Rice was observing the toadfish noting the male would hoot if he wanted to spawn with a female and grunt if something got too close to the eggs he’s fertilized, he grunts. Looking at the spectrogram images of these “simple” sounds he noticed “there was some weird stuff,” he said.
Typically you would expect the normal linear variations in pitch and volume and as Rice studied the sounds noticed non-linearities as well. These are generated by the interaction of two different sounds, and can convey much more information than linear sound.
Rice and his team tested their theory and to make sure the sound was in fact coming from the swim bladder, would paralyze one chamber and set them free but the sounds with complex signals vanished. Although Rice notes there is a slim chance the toadfish’s complex calls are meaningless products of evolution, he does feel these messages can show the individual animal’s identity much like how a penguin knows its parents calls.
Next up for Rice and his team? Paralyzing one swim bladder and observing communication. If having one of their swim bladders causes breakdown in communication it could be the sign of a new frontier of fish communication research.