This Tiny Fish Can Make Sounds That Rival an Airplane or an Elephant—Now, Scientists Know How

Transparent and just half an inch long, male Danionella cerebrum can make noises of more than 140 decibels

small translucent fish in water swimming to the left
Because the fish are translucent and they lack skulls, they're a favorite research subject of neuroscientists. Ralf Britz / Senckenberg Research Institute and Natural History Museum

How can such a tiny fish make such loud noises?

Scientists have long asked this question about the male Danionella cerebrum, which measures less than half an inch long, yet produces noises of more than 140 decibels, when measured next to the fish. That puts it in the same range as a firecracker, or a jet engine taking off some 330 feet away.

The unusual fish lives in Myanmar, swimming in the streams that run through the Bago Yoma mountain range.

Historically, neuroscientists have been the researchers most interested in D. cerebrum, because it has the smallest known brain of any vertebrate on the planet. The fish are transparent and they don’t have skulls, so the researchers can easily see and access brain tissue. But while studying the fishes’ brains in a laboratory, a team of researchers in Germany recently decided to investigate the cacophony coming from the creatures’ tanks.

“People were just walking past the fish tanks, and they could hear these sounds and were wondering where they were coming from,” says study co-author Verity Cook, a neuroscientist at Charité University in Germany, to BBC News’ Matt McGrath.

To figure out how such petite fish can make so much noise, scientists put groups of three to four fish inside a tank. Then, as the D. cerebrum swam around, the researchers captured high-speed videos, they report in a new paper published Monday in the journal Proceedings of the National Academy of Sciences.

After analyzing the footage, they saw that the fish were making the sounds with their swim bladders. A special muscle pulls one of the fish’s ribs against a piece of cartilage with an indentation. Then, when the fish releases the rib, it collides with the swim bladder to make a loud drumming noise.

Tiny fish make sounds as loud as firecrackers

The team also studied the fishes’ genes and found that the special rib-pulling muscle has more endurance than other muscles, so it can pulse quickly for a long time. This fatigue-resistant muscle allows the fish to make lots of rapid-fire percussive sounds in a row.

“There’s tension built up in this contraction,” Cook tells New Scientist’s Chen Ly. “When that is very rapidly released, [the rib] strikes the swim bladder, which produces the drumming sound.”

Only males make the drumming sound—and it seems their bodies have evolved to be able to do so. The rib bone that makes the noise is larger and more rigid in males than in females.

Other fish also make loud noises using their swim bladders, including mating black drum fish, which made headlines for possibly keeping Florida residents up at night. And male midshipman fish make droning mating calls that can reach 130 decibels.

But the 140-decibel calls of D. cerebrum are “unusually loud” for their small size, compared to other vertebrates, the researchers write in the paper. Trumpeting elephants can only reach 125 decibels, per a statement from the Senckenberg Research Institute and Natural History Museum in Germany.

Though the team figured out how the tiny fish make so much noise, they still don’t know for sure why they do it. But they have a few theories. It’s possible the fish make the sounds to find each other in murky waters. Or, maybe, because only males make the sound, it’s meant to help attract a mate or warn other males to steer clear.

“We know that when you have maybe like eight males together in a large tank, then three of them will dominate the sound production and the other ones will be quiet,” says Cook to BBC News. “So, we think there is some sort of hierarchy.”

D. cerebrum has a history of surprising researchers. In 2021, neuroscientists who’d been studying the fish in laboratories realized they’d been working with an unnamed and unidentified species. So, they gave it a name—one that reflected the fish’s importance to the field of neuroscience. The species name, “cerebrum,” refers to the largest part of the brain.

“On the outside, they look very similar to different species of Danionella, and it’s only by studying their skeleton that we actually realized that the neurophysiologists might actually be working with a new species, one that hasn’t been described before,” said Kevin Conway, an ichthyologist at Texas A&M University, to Texas Standard’s Michael Marks at the time. “It was swimming in the tanks of neurophysiologists before it’s actually been given a name.”

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