Small Brains & Gunshots

Some critters have all the luck. The platypus might be the strangest animal on the planet, or, at least, possess the highest number of bizarre traits. But the duckbill doesn’t have a monopoly on interesting attributes.

In the project’s early days, we investigated the snapping shrimp, also known as the pistol shrimp. This Lynchian entity packs a freakish arm that can unleash sounds louder than rocket launches. The two-inch shrimp is so loud that it interferes with submarine sonar.

As it turns out, the ocean is rather noisy. In addition to the snapping shrimp, several fishes have developed the ability to produce ultra-loud emanations, such as the plainfin midshipman and the black drum. With the nature of sound – it attenuates as it propagates – and the volume of the oceans, it’s likely that a slew of other rackety aquatic creatures populate the seven seas.

In 2021, researchers discovered a species of fish in the murky streams on the slopes of the Bago Yoma mountain range (great name) in Myanmar. This fish did not appear out of the ether; previously, scientists thought this piscine vertebrate was Danionella translucida, another fish from Myanmar. Instead, today’s topic belongs to a distinct species, known as Danionella cerebrum.

Researchers scooped up some of these fishes and took them to a lab in Germany. There, they noticed something odd. As scientists walked by the tanks, they heard mysterious percussive sounds. After investigation, they realized the noise came directly from the tiny fish.

And the volume was cranked, especially for a fish the size of Danionella cerebrum. These critters come in at just 12 millimeters in length, yet the rhythms they clanked registered at 140 decibels! Normally, the loudest sounds come from the biggest entities in the ocean, which makes this fish and the snapping shrimp all the more outstanding. The sounds from the tanks paled in comparison to the shrimp’s 218 decibels, but 140 is still the level of a gunshot.

The video above captures the emanations of Danionella cerebrum. Fret not, you won’t hear anything on the grade of a gunshot or firecrackers. Sounds of that level only transpire in proximity to the fishes. Sound tends to dissipate rather quickly over distances (which makes the really clamorous sounds all the more impressive). Still, the levels are rather remarkable for a creature less than half an inch long.

The din comes from the males, who contract muscles around their swim bladders, which activates a piece of cartilage to bang on the bladder. Not only does it sound like a drum but functions as one, too. Though scientists are not yet certain about why the males produce these sounds, they theorize that the process is an evolutionary method developed to display dominance in the cloudy waters in which they live. If one cannot see well, use sound! Loudness also appears to be a way to stand out, as the noisiest males drown those who cannot compete.

The discovery of this loudness happened by accident, as researchers walked by tanks filled with the fishes. If this characteristic had not been known, why were fishes from Myanmar in a lab in Germany in the first place?

As it turns out, the gunshot drumming of Danionella cerebrum is the second quirk of the species.

The image above illustrates one important detail: they are translucent. The genus Danionella is a diminutive form of a larger grouping of fish, the Danionins. These swimmers are some of the smallest in the world, and the Danionella are even tinier. This size grants Danionella cerebrum with another superlative: the world’s smallest known vertebrate brain, measuring just 0.6 cubic meters.

This distinction bestows the fishes their species name of cerebrum, and it’s their brains that make them the hot topic in neuroscience research today. Because we can see their brains through their skin and because the brains are so small, scientists can study the brains while the fish are still alive on a cell-by-cell basis. They can watch how individual brain cells react to all sorts of stimuli. This investigation could unlock answers to how the organs work in other species, including humans.

So, field researchers transported the fishes from Asia to Europe to study their brains, but discovered they also had musical talent. When your brain is small, crank your music to 11!