From mysterious clicking noises in a fish tank in a lab, to humming haddocks and singing toadfish, scientists are discovering the wonder of underwater communication.
When you think about how fish communicate with each other, it might conjure little more than a watery silence, punctuated by the odd bubble.
In reality, however, “the oceans are alive with sound”, says Aaron Rice, a researcher at Cornell University in Ithaca in New York. Clicks, grunts, plops and screeches are just some of the sounds fish use to signal to those around them underwater. Some, such as toadfish, sing beautiful songs to each other, and others, such as herring, communicate using their digestive tracts – more on this later. They use these signals for a variety of reasons: to warn off competitors, sound the alarm and even to woo potential mates.
Clues that fish are chattier than we might have given them credit for have floated around since the 4th Century, from the works of Aristotle to whispers from traditional fishing communities, says Rice. But our ability to eavesdrop on fish has been limited by the devices used to record underwater. (Read more about why scientists are eavesdropping on the ocean in this article by Katherine Latham.)
Acoustic monitoring has come a long way since the 1930s, and scientists are now using underwater microphones, called hydrophones, to listen in on the marine world. Technology invented in World War Two to scout for submarines has helped us listen to the ways fish talk to one another in the depths of oceans, rivers and lakes.
One tiny fish appears to use a deafening sound to establish a hierarchy in the fish tank
Out of the estimated 34,000-35,000 ray-finned fish species alone, which include cod, tuna, trout and salmon, only around 4% have been studied for their sound production. But Rice’s research suggests we have only scratched the surface of the mysterious world of fish communication. Up to two-thirds of fish could be making noises underwater, he says.
In February 2024, researchers in Germany discovered one tiny transparent fish called Danionella cerebrum, which produces a sound so loud it could rival a pneumatic drill. They discovered it after hearing mysterious clicking noises coming from the fish tanks in their laboratory. The 12mm- (0.5in) long fish uses an organ called a swim bladder to produce sounds as loud as 140 decibels in the water around it. The researchers aren’t clear what purpose this noise has, but only male fish appear to make the sound and it may be used to establish a sort of hierarchy in the fish tanks. (Read more about Danionella cerebrum and its deafening calls in this story by the BBC’s environment correspondent Matt McGrath.)
