The Fish That Uses Its Tongue as a Fishing Rod

In the shadowy depths of South America’s freshwater rivers, where murky water hides both predators and prey, one small catfish has developed a hunting method so strange, it sounds made-up.

It doesn’t chase.

It doesn’t ambush.

It doesn’t use venom or speed.

Instead… it goes fishing.

With its own tongue.

Meet the Candiru-acu, a bizarre little catfish that uses a fleshy extension inside its mouth like a built-in fishing rod—complete with bait.

Yes. This fish has evolved to fish.

Not Your Average Catfish

The Candiru-acu (Cetopsis candiru) is part of the Cetopsidae family, a group of catfish found mainly in the Amazon and Orinoco river basins. Most members of this group are scavengers, feeding on dead fish or animal matter drifting along the river bottom.

But the Candiru-acu is different.

It’s a predator, and a creative one at that.

Rather than searching blindly for food in dark water, this little fish waits patiently—and uses part of its body as a tool to attract prey.

A Tongue with a Trick

Inside the Candiru-acu’s mouth is a long, flexible extension that resembles a tongue. But it’s no ordinary tongue.

It has evolved into something closer to a lure—a movable, fleshy filament that the fish can wiggle and twitch like a worm.

This strange “tongue lure” sticks out just slightly from the fish’s mouth and moves in a way that mimics the motion of a small aquatic creature—exactly the kind of snack that nearby fish or invertebrates might want to grab.

But the moment a curious victim gets too close, the Candiru-acu snaps its jaws shut—trapping its prey in a split second.

It’s fishing. But the rod, the bait, and the trap are all built into its mouth.

Nature’s Angler

This strategy is known in the scientific world as lingual luring—using a tongue or mouthpart to mimic prey and attract other animals.

It’s similar to what we see in some frogs, turtles, and especially the famous deep-sea anglerfish, which dangles a glowing lure from its head.

But the Candiru-acu is one of the only known fish to use its tongue this way.

And while it doesn’t glow, it doesn’t need to. The subtle movement in dark water is enough to get curious creatures close—and that’s all it needs.

Small But Vicious

Despite its cleverness, the Candiru-acu isn’t a large or flashy fish. It usually grows only up to 10–15 cm long and looks rather plain compared to the vibrant colors of other Amazonian species.

But what it lacks in size, it makes up for in ferocity.

Researchers have discovered that the Candiru-acu is also known to feed on the internal organs of larger, dead animals, entering through openings and eating from the inside out. That earned it a bit of a scary reputation.

But when it comes to live prey, it’s the tongue-lure strategy that makes this fish truly unique.

Surviving in Darkness

In the muddy waters where this catfish lives, vision is nearly useless. The fish rely mostly on vibration, chemical cues, and movement.

That’s why the tongue lure is so effective.

It creates the illusion of life—a little twitch, a subtle flick—and in a world where food is scarce, that’s often enough to tempt a bite.

The Candiru-acu doesn’t need to swim fast or chase its prey. It lets the prey come to it.

Like a fisherman sitting still with his rod in the water, it waits. Calm. Focused. Ready.

Evolution’s Creativity on Display

The Candiru-acu’s hunting style shows just how creative evolution can be. Instead of giving the fish bigger teeth, stronger muscles, or better eyesight, nature gave it something better:

A built-in lure.

It's a reminder that in the animal kingdom, brains can beat brawn, and that sometimes, the weirdest solutions work the best.

Not Dangerous to Humans

Despite its scary reputation and dramatic hunting methods, the Candiru-acu is not dangerous to humans.

It won’t attack swimmers, and it’s far more interested in worms, small fish, or decaying organic matter.

The infamous cousin of this fish, Vandellia cirrhosa (the parasitic “urethra fish”), is often confused with it—but they are not the same species.

The Candiru-acu, though creepy to some, is simply another marvel of the natural world—doing what it must to survive in a tough environment.

A Fish That Fishes

In the end, this strange little catfish proves that tools don’t have to be made from wood or metal.

Sometimes, evolution builds tools right into the body.

A tongue that looks like a worm.

A mouth that acts like a trap.

A fish that goes fishing—with itself.

And in the dark waters of the Amazon, that’s all it needs.