- Written by Matt McGrath
- Environment correspondent
Hear the very loud sound of Danionella's brain in action
Scientists in Berlin have discovered that a small, transparent fish makes a loud sound like a jackhammer.
They were asked to investigate after hearing mysterious clicking noises coming from their laboratory's aquariums.
They found that the fish, Danionella cerebri, emits a powerful rhythm on an organ called the swim bladder.
In water close to the fish, it emits a sound of up to 140 decibels, which is as loud as a gunshot.
Researchers believe this 12mm-long species is the loudest fish for its size ever found.
They believe that drumming may be a form of social communication.
In most natural worlds, the larger the animal, the louder the sound.
It's a different story underwater – where the tiny marine species is now one of the noisiest ever discovered.
Scientists have known that other creatures, such as the aptly named pistol shrimp, can make very loud noises while hunting other species, up to about 200 decibels.
Danionella is prized by science because its transparency means you can see its brains in action and this allows researchers to study its behavior more closely.
Another noisy fish is the very large black drum
But while working with these fish in their lab in Germany, scientists noticed something strange.
“People were walking by the aquariums, and they could hear these sounds, and they were wondering where they were coming from,” said Verity Cook, lead author of the study and a doctoral student at Charite University in Berlin.
“It turns out it comes from the fish themselves. This is unusual, because they are very small and very noisy.”
Using a combination of microphones and video cameras, the research team was quickly able to determine how loud the sound was.
“At a distance of one object, the sound is about 140 decibels, and that's how loud we think other fish can hear it,” she told the BBC.
“Sound weakens with distance, so at one meter away, its amplitude is about 108 decibels.”
This is still roughly equivalent to the noise made by the bulldozer.
Much of this sound is reflected back into the water, so when humans stand next to aquariums, they hear these pulses as a continuous humming sound.
While fish including the Plainfin Midshipman, Black Drum and others are louder, they are all much larger than Danionella.
“In terms of communication signals, I haven't been able to find another animal this size that makes noises this loud,” Cook added.
Researchers believe that the drumming mechanism used by fish is a highly advanced tool.
All bony fish have a swim bladder, a gas-filled organ that helps them stay underwater.
Many species use their muscles to drum on this bladder to make sounds, but Danionella goes several steps further.
When its muscles contract, they pull on a rib, creating tension with a piece of cartilage located inside the muscle.
When the cartilage is released it hits the swim bladder.
Only males of this species make this sound, and they do so only in the company of each other. Some are higher than others.
“We know that when you have approximately eight males together in a large tank, three of them will dominate sound production and the others will be quiet,” Cook said. “So we think there is some kind of hierarchy.”
Researchers believe that development in Myanmar's murky waters played a role in developing this ability to make loud noise to help them communicate.
“Evolution has come up with a lot of interesting ways to solve a lot of interesting problems,” Ms. Cook said.
“And we shouldn't assume that we know how things work just because of how things work in other species.”
It was the study published In the Proceedings of the National Academy of Sciences.
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