This little 12 millimeter fish is louder than a pistol shot

Danionella cerebrum is a small fish about twelve millimeters long that occurs in Myanmar. It is of interest to researchers around the world because its skin is transparent. This allows you to examine his brain (while he is still alive) – hence the Latin name “cerebrum”.

There is a research group at Charité University in Berlin studying Danionella cerebrum. While working with the fish, something was noticed: strange sounds were coming from the aquarium.

The researchers investigated the matter and discovered that Danionella cerebrum is interesting not only because of its transparent skin. The small fish is also extremely noisy. In one study, Charité researchers discovered that the fish can produce sounds of up to 140 decibels. For comparison: a jackhammer has about 110 decibels. A pistol shot is about 130 decibels. At 140 decibels, a jet engine is about as loud as a fish.

Since the fish live in water, the volume of the sound decreases significantly. Of course, to the researchers at the Charité laboratory, it didn’t sound like a shooting. Much of this sound is reflected back into the water, causing people standing next to the aquarium to hear the sound more as a continuous hum.

“People were walking past the aquariums, hearing these sounds and wondering where they were coming from,” Verity Cook, lead author of the study and a PhD candidate at Charité in Berlin, told the British BBC.

«It turned out that they came out of the fish themselves. And that’s extraordinary because they’re so small and so loud.”

Using a series of microphones and video cameras, the research team was soon able to discover how loud they were. The researchers determined the peak value of 140 decibels at approximately a body length distance from the fish. They therefore assume that conspecifics perceive each other so loudly. At a distance of one meter, the noise was about 108 decibels – still the volume of a bulldozer.

According to the researchers’ findings, Danionella cerebrum probably uses these sounds for communication and not – like other species – for hunting.

“In terms of communication signals, I couldn’t find any other animal of this size that makes such loud noises,” says Cook, commenting on her research results. In fact, there are many other species that are also very noisy, such as mantis shrimp. But these are also considerably larger than Danionella cerebrum.

In their study, the researchers show how the sound is created. All bony fish have a swim bladder, a gas-filled organ that helps them stay underwater. Many species drum their muscles on this bladder to produce sounds, but Danionella cerebrum goes one step further.

When the fish contracts its muscles, they pull on a rib, putting tension on a piece of cartilage inside the muscle. When the cartilage is released, it hits the swim bladder.

Only the males of this species make this sound, and they only do it in company. Some are louder than others. “We know that if you have about eight males together in a large aquarium, three of them will dominate the noise production and the others will be silent. “So we believe there is some kind of hierarchy,” Cook says.

Researchers believe that development in Myanmar’s murky waters played a role in developing this ability to make a lot of noise to facilitate communication. “Evolution has come up with a lot of interesting ways to solve a lot of interesting problems,” Cook says.