In this lab image, the toadfish’s twin bladders
are visible in the middle of its body.
There’s nothing like a bizarre fish call to shake you out of your complacency about the universe. With that in mind, we bring you the bottom-feeding three-spined toadfish, which produces its foghorn hoots and guttural grunts by vibrating the muscles around its two swim bladders, the sacs of air that keep it afloat. And these aren’t just any hoots and grunts, a new study reveals—some of these cries have qualities that have been seen the animal kingdom over, from babies’ cries to frog calls to bird song, but never before seen in fish, though fish have been known to make an incredible array of sounds (really!).
These qualities, called nonlinearities, are harmonics and dissonances that are overlaid on the linear qualities—rising and falling pitch, for instance—of a call, like elaborate icing on an otherwise plain cake. Birds are the virtuosos of nonlinear calls, using their double-piped throats to create complex songs that no wimpy human larynx can replicate, but the cries of distressed human babies have nonlinearities, as do the calls of many other creatures.
Three-spined toadfish are unusual among fish for having two swim bladders, and it turns out this is the key to their odd songs. The two bladders are controlled by different nerves and muscles, and when the researchers disabled one bladder, the toadfish could no long create nonlinearities. The cries of two closely related toadfish species with single swim bladders were also decidedly linear, the group found, confirming the finding.
But what do these cries mean to the toadfish? In other species, nonlinearities might help animals identify an individual or help signal danger, but it’s anyone’s guess what the toadfish is hearing. Is it a “hey baby” or a “back off, buster”? The lead researcher is looking forward to picking this apart (via New Scientist): “This is where things start to become exciting.”
Image credit: Aaron Rice, Cornell University