It’s good to have a plan in case of emergency. If there’s a fire, take the stairs to the ground floor. If a bird tries to eat you, say “ERK ERK ERK” by grinding your spine bone against your shoulder bone until it drops you. That latter one will work best if you’re a certain kind of catfish (but feel free to try it and report back).
Our glossary of thorny catfish phrases is getting a little more complete, thanks to Lisa Knight and Friedrich Ladich at the University of Vienna. Thorny or “talking” catfish make up the family Doradidae and are native to South America. Back in 1997, a study by Ladich suggested that these catfish choose their distress calls based on the type of predator that has them in its grasp.
That research thread had since been abandoned. Picking it up again now “happened by chance,” Ladich says. “We had a large number of catfish in our lab,” he explains (who hasn’t been there?), and his student Lisa Knight wanted to investigate their alarm sounds. So the scientists set out to see whether Ladich’s hypothesis from the nineties held up.
One of the sounds they studied was a “stridulation” noise, which Doradidae catfish make by moving their fins back and forth to loudly rub their bones together inside their bodies. (The recording below is a Megalodoras uranoscopus demonstrating this.) Also in their repertoire is a “drumming” sound. They make this by rapidly vibrating their swim bladder, a gas-filled organ they use to control their buoyancy.
To find out how thorny catfish use those two sounds, the researchers pretended to be predators. Imitating birds, they snatched each catfish out of the water, holding it up by two of its spines. Most fish immediately started protesting. The researchers recorded the sounds until the fish quieted down a minute or more later, then put them back in the tank. To imitate a large, hungry fish, the researchers gripped catfish in the same way in a tub of water, and recorded them with an underwater microphone.
The earlier study had hinted that catfish use scraping stridulation sounds when seized by birds, and use drumming sounds in response to underwater predators. The stridulation sound has a higher frequency, making it audible by birds, while the lower-frequency drumming sound would correspond to the hearing of other fish. But this time Knight and Ladich found no difference in how the catfish responded to predators. All five species they studied used stridulation sounds during both air and water attacks. Drumming was less common overall, and more likely to happen underwater.
Now Knight and Ladich think stridulation is a universal alarm sound, while drumming is for communication between fish. Besides being surprising, the bone-scraping sound may point out to potential predators just how spiny the catfish is, making them rethink swallowing it. And several studies have observed catfish drumming on their swim bladders to communicate with each other.
According to his new hypothesis, Ladich says, “stridulation sounds should be loud enough to deter predators [both] underwater and in air.” Take note for your own worst-case-scenario planning.
Image: Oxydoras niger by Jonathan Armbruster (via Wikimedia Commons). Audio: courtesy of Friedrich Ladich.
Knight L, & Ladich F (2014). Distress sounds of thorny catfishes emitted underwater and in air: characteristics and potential significance. The Journal of experimental biology PMID: 25267850