The Fish That Can Swallow Prey Larger Than Itself

Quick Take

• This tiny 10-inch fish pulls off a feat that should be physically impossible, and scientists have finally caught it on camera. See the footage details →
• The black swallower's superpower has a dark irony: the very ability that keeps it alive can also kill it. Discover the fatal irony →
• Its stomach does something no other organ in the animal kingdom quite matches, and the anatomy behind it is stranger than you'd expect. Explore the stomach anatomy →
• An expedition mapped over 11,000 square kilometers of seafloor and found 20 new species, yet the black swallower still managed to steal the spotlight. See what else was found →

The deep ocean is full of animals that seem almost unreal. There are fish with enormous teeth, creatures that produce their own light, and animals that can survive under pressures that would be crushing to other organisms. The black swallower fish is the species in this Instagram story, and it’s famous for its ability to swallow prey larger than its entire body! 

This discovery is one of 20 species spotlighted in the Instagram post that were recently captured on camera in the deep ocean. The list includes deep-sea corals, sharks, ghost sharks, lizardfish, octopuses, squat lobsters, and numerous other animals.

The first real footage of the black swallower fish in action was taken deep in the waters around Trinidad and Tobago, and what scientists saw has made them very excited. Let’s take a deeper look at this exciting oceanic sighting.

A Unique Fish in a Little-Known World

A recent expedition mapped about 11,335 square kilometers of uncharted seafloor and collected more than 700 specimens. At a depth of about 1,259 meters, they discovered the swallower fish. The first sign that the species could swallow excessively large prey came when scientists looked at its translucent body and saw that what it had eaten was considerably larger than the fish itself. From there, they looked more closely at the fish.

The black swallower fish (Chiasmodon niger) may look like a larger species, but it’s actually quite small, at only about 10 inches long. It has a long, narrow body covered in dark, scaleless skin. Its coloration is generally black or very dark brown, which is an effective appearance for an animal living in the darkness of the deep ocean. 

Although the recent discovery was made in the waters near Trinidad and Tobago, this species is found in numerous places around the world, including the Atlantic, Pacific, and Indian Oceans. The species is particularly widespread in the Atlantic, including the waters of the Caribbean and Gulf of Mexico. So, the sighting of the fish itself isn’t so unique. However, this is one of the first times scientists have captured video of the fish swallowing large prey.

How It Can Swallow Prey Larger Than Itself

The black swallower’s head is relatively large compared to its body. Its mouth is one of its most noticeable features, and it contains numerous sharp, backward-pointing teeth, some of which are quite large. They enable the black swallower to hold onto prey as it tries to escape.

The black swallower has an extremely distensible stomach that can stretch dramatically to accommodate a larger meal. This adaptation is particularly useful in the deep sea, where food can be unpredictable. Unlike animals living near the surface, deep-sea predators cannot necessarily depend on finding another meal a few minutes or even a few hours later. The deeper parts of the ocean are generally cold, dark environments. Down there, encounters between predators and prey can be separated by considerable amounts of time.

Research shows that the black swallower can consume prey up to roughly twice its own length and as much as 10 times its body mass. In order to accomplish this feat, many parts of the fish’s anatomy must work together. First, its jaws open extraordinarily wide, with enough room to take hold of prey that seem far too big for the fish’s head. Then, its hooked teeth hold the prey in the mouth and push it back toward the stomach. Finally, the fish’s stomach stretches dramatically to finish the process. 

There is a Downside

Despite the incredible feats of the black swallower fish, there is a downside to the uncanny ability to swallow prey larger than itself, and that’s the potential to eat too much. If a black swallower consumes prey that is way too large, the fish may not be able to digest it before the meal begins to decompose, and that can become fatal.

As the prey decomposes, gases can accumulate inside the stomach. The enormous stomach is already stretched around the meal, and gas buildup can make the fish increasingly buoyant. Eventually, that can carry the fish upward toward the ocean surface. This unfortunate situation happens from time to time. Many black swallowers have actually been discovered dead at the surface, with their enormous meals still visible inside their distended stomachs. 

In the end, eating a gigantic meal may mean survival when food is scarce. But choosing a meal that is too large can turn that advantage into a deadly mistake.

You’re Unlikely to See It in the Wild

Though witnessing this act in real time would be fascinating, you’re highly unlikely to see it occur in person or even to spot the species in the water at all. 

The species generally lives hundreds to thousands of meters beneath the ocean surface, typically at a depth range of approximately 700 to 3,000 meters, placing it primarily in the deep pelagic environment. This puts it far below the familiar world of coral reefs, coastal waters, and recreational diving.

Even if you were down there, visibility would be almost zero. Very little sunlight penetrates to these depths, and deeper down, it’s essentially complete darkness. 

A Reminder of How Little We Know About the Deep

This unique sighting is just another reminder of how little we really know about the creatures in our oceans. The more we discover, the more we realize how truly unique and even alien-like the life down there can be. 

The black swallower fish may not be the newest discovery or most scientifically mysterious animal, but it’s certainly one of the most unforgettable. A small black fish, swimming more than 4,000 feet below the surface, carrying an enormous meal inside a stomach stretched almost beyond recognition, is a perfect example of why the deep ocean continues to surprise scientists—and why there is still so much left to uncover beneath the waves.