Barely the size of a thumbnail, a Myanmar fish has the smallest brain of any vertebrate. This interested neuroscientists, who were studying them in the lab when they heard the pint-sized creature making sounds of over 140 decibels.
Danionella cerebrum‘s transparency and lack of a skull make them the perfect test subjects for brain studies. As researchers walked past the aquariums, they continually heard peculiar clicking sounds. They decided to investigate further. It is well known that the fish make these noises, but no one knew how or why.
The researchers filmed the fish with high-speed cameras and discovered that the noise came from the fish’s swim bladder.
How can the tiny glassfish @danionella cerebrum, just over 1 cm long, produce high-amplitude communication sounds exceeding 140 dB? We found that it uses a fascinating drumming mechanism involving acceleration at over 2000 g:https://t.co/LOkp7UObLJ
1/10x slo-mo video has sound pic.twitter.com/QDnjYkvNCF— Benjamin Judkewitz (@benjulab) February 26, 2024
They use one rib as a drumstick
The fish makes the noise as its ribs hit the surface of the swim bladder. A special muscle pulls the rib against some cartilage. When it is released, it hits the swim bladder like a drum.
Analyzing further, scientists learned that the rib-pulling muscle has more endurance than other muscles in the fish’s body. This fatigue resistance allows it to make repetitive drumming.
“There’s tension built up in this contraction. When that is very rapidly released, [the rib] strikes the swim bladder, which produces the sound,” lead author Verity Cook told New Scientist.
Only males make the drumming noise. The particular rib that acts as a drumstick is larger and more rigid in males than in females.
The purpose of the drumming remains elusive. It could be part of mating behavior, or to show aggression or dominance.
“When you have maybe eight males together in a large tank, then three of them will dominate the sound production, and the other ones will be quiet,” explained Cook. “So we think there is some sort of hierarchy.”
The other possibility is that the fish use the noises to help find each other in dark water.
They are not the only fish that make noise. Pistol shrimp make noises up to 200 decibels, and midshipman fish mating calls can reach 130 decibels. So a fish that makes noise is not necessarily surprising. But the amount of noise that this minuscule creature produces is highly unusual.
