You’ve probably seen the meme. It’s a fish with a face only a mother (or a very dedicated marine biologist) could love, paired with a name that sounds like a middle-school insult. The bony-eared assfish is very real. It isn't a Photoshop prank or a glitch in the taxonomic system. Scientifically known as Acanthonus armatus, this creature lives in the kind of crushing darkness that would flatten a human into a pancake in seconds.
It's a record-breaker, too. Not for speed. Not for beauty. But for having the smallest brain-to-body weight ratio of any teleost (bony) fish. Basically, it’s all body and very little "thought."
What exactly is a bony-eared assfish?
Let’s get the name out of the way because that’s why you’re here. The "bony-eared" part is literal. It has massive, prominent spines sticking out from its gill covers, which look a bit like jagged ears. The "assfish" part is a bit more mysterious to the average person, but it stems from the Greek word onos, which can mean donkey or hake. Since this fish belongs to the Ophidiidae family—commonly known as cusk eels—the "ass" part is a linguistic hand-me-down from ancient descriptions of similar-looking, tapered fish.
It looks like a giant tadpole. A grumpy, bulbous-headed tadpole that can grow up to about a foot long. Its skin is soft, almost gelatinous, and it lacks the heavy scales you’d find on a snapper or a bass. Why? Because at 4,000 meters below the surface, building a heavy armored skeleton is an expensive use of energy that most deep-sea creatures simply can’t afford.
It’s a master of doing almost nothing.
When researchers observe the bony-eared assfish in its natural habitat—the bathypelagic and abyssopelagic zones—they don't see a predator darting around. They see a drifter. It hangs in the water column, barely moving, waiting for a snack to bumble into its path.
Life at 14,000 feet below the waves
The ocean is deep. Really deep. The bony-eared assfish has been found at depths exceeding 4,400 meters (about 14,435 feet). To put that in perspective, if you dropped the Burj Khalifa into the water, you’d need to stack five and a half of them to reach where this fish is chilling.
Down there, the pressure is roughly 400 times what we feel at sea level. The water is barely above freezing. Light doesn't exist. In this environment, the Acanthonus armatus has evolved some pretty weird trade-offs.
- The Brain Issue: As mentioned, it has a tiny brain. But it also has an oversized vestibular system. This means that while it might not be solving calculus, it is incredibly sensitive to changes in balance and vibrations in the water.
- The Skeleton: Its bones are light and poorly mineralized. If you brought one to the surface too quickly, it would essentially fall apart.
- The Diet: It isn't picky. It eats small crustaceans and whatever organic "marine snow" drifts down from the sunlit world above.
Honestly, the life of an assfish is a lesson in extreme minimalism. It has stripped away everything unnecessary—dense muscle, complex gray matter, hard scales—just to survive in a place where food is scarce and the weight of the ocean is trying to crush it into paste.
The science behind the "Assfish" name
The genus name Acanthonus comes from the Greek akantha (spine) and onos (hake or donkey). The species name armatus means "armed," referring to those intense spikes on its head.
We’ve known about them since the late 19th century. The HMS Challenger expedition, which basically birthed modern oceanography between 1872 and 1876, was the first to drag these "monstrosities" up from the depths. Imagine being a Victorian-era scientist, pulling a net up from the mid-Atlantic, and finding a gelatinous, big-headed creature with thorns on its ears. "Assfish" probably felt like a polite description given the alternatives.
Why the small brain matters
There’s a lot of talk in biology about encephalization—the ratio of brain size to body size. Humans are at one end of the spectrum. The bony-eared assfish is at the dead end of the other.
But don't call it stupid.
In the deep sea, a large brain is a liability. Brain tissue is metabolically expensive; it requires a lot of oxygen and calories to keep the lights on. If you’re living in a desert (which the deep seafloor essentially is), you don't want a Ferrari engine for a brain if you only have a teaspoon of gas. The assfish is the ultimate fuel-efficient vehicle. It keeps the sensory systems it needs to find food and ignores the rest.
It’s also worth noting that its ears—those "bony" parts—are actually part of a very specialized hearing and balance setup. Even though the brain is small, the parts of it dedicated to "hearing" the vibrations of a tiny shrimp nearby are quite developed. It's specialized, not simple.
Where can you see one?
You can’t. Well, not alive.
Keeping a bony-eared assfish in an aquarium is currently impossible. The pressure change alone would kill it long before it reached the surface, and even if you used a pressurized retrieval canister, we don't really know how to replicate the specific chemistry and stillness of the abyss.
However, if you're a fan of preserved specimens, major natural history museums like the Smithsonian in Washington D.C. or the Natural History Museum in London have them in their deep-sea collections. They usually look like pale, shriveled versions of their deep-sea selves because the alcohol used for preservation draws out the moisture from their gelatinous bodies.
Misconceptions about the Assfish
People think it's a "failed" animal because of the brain size. That’s just wrong. It’s a highly successful specialist. It has survived for millions of years in an environment that would kill almost any other vertebrate on Earth.
Another myth is that they are rare. They aren't necessarily rare; they are just hard to get to. Every time we send a ROV (Remotely Operated Vehicle) into the abyss, we find that the deep sea is teeming with life that we previously thought was "rare" simply because we didn't have the keys to the front door.
Taking Action: How to explore the deep sea (virtually)
If the bony-eared assfish has piqued your interest in the weirdness of the abyss, you don't need a submarine to see more.
- Follow MBARI: The Monterey Bay Aquarium Research Institute (MBARI) regularly posts high-definition footage of deep-sea expeditions. They haven't caught an assfish on camera every day, but their library of "weird stuff at 4,000 meters" is unbeatable.
- Check the NOAA Ship Okeanos Explorer: They do live streams of their dives. You can literally sit on your couch and watch a robot arm poke things on the ocean floor in real-time.
- Support Deep-Sea Conservation: The habitat of the assfish is increasingly under threat from deep-sea mining interests. Organizations like the Deep Sea Conservation Coalition work to ensure these weird creatures don't lose their homes before we even get a chance to name them something better.
The bony-eared assfish is a reminder that the world is much bigger, darker, and stranger than our surface-dwelling brains can usually comprehend. It's a specialist in a world of extremes, proving that you don't need a big brain to be a total survivor.
Next time you feel a bit slow or out of place, just remember: there is a fish in the ocean named for its butt and its ears, and it's doing just fine 14,000 feet down.