The Fish That Uses Mirrors Inside Its Eyes

Deep in the twilight zone of the ocean, where sunlight barely reaches and the pressure would crush most animals, a strange little fish drifts silently through the water. At first glance, it looks like just another odd deep-sea creature—transparent body, weird shape, ghostly presence.

But look closer. There’s something different about its eyes.

Unlike most animals that use lenses to focus light, this fish uses something far more unusual—mirrors.

Yes. Real biological mirrors.

Meet the spookfish (Dolichopteryx longipes), a deep-sea fish with some of the weirdest eyes ever discovered in the animal kingdom.

The Deep Sea Dilemma

Living in the deep sea comes with serious challenges. Food is scarce, predators are everywhere, and worst of all—it’s almost completely dark.

Most animals that live in this part of the ocean have evolved special eyes to survive the darkness. Big eyes. Sensitive retinas. Night vision levels that put owls to shame.

But the spookfish took things a step further.

Instead of just making its eyes bigger, it evolved a completely different visual system—one that combines lenses and mirrors in the same eye. It’s the only known vertebrate to do this.

Two Eyes in One

The spookfish doesn’t just have strange eyes—it has double eyes. Literally.

Each of its eyes is split into two parts:

• One part points upwards to catch the faint light from above.

• The other part points downwards to spot bioluminescent creatures in the deeper dark.

The upper part works like a normal fish eye—it uses a lens to focus light, just like humans do.

But the lower part? That’s where things get wild.

Instead of a lens, it uses a curved mirror made of guanine crystals to reflect and focus light onto the retina. It's like having a natural telescope inside your head.

How Does a Mirror Eye Work?

Here’s the crazy part: these mirrors aren’t like the ones in your bathroom.

They’re made of microscopic plates arranged at precise angles to reflect incoming light and direct it toward the photoreceptors. The curve of the mirror helps focus the image, just like a telescope mirror.

This design lets the spookfish see objects that are below and behind it, while still watching the light from above.

No other vertebrate has been found with this kind of mirror-based vision system. It’s a one-of-a-kind adaptation, perfectly built for the deep sea’s visual chaos.

Why Mirrors Instead of Lenses?

Light behaves differently in water, especially at great depths. Lenses can only bend and focus so much of the dim light. But mirrors? They can reflect and concentrate it more efficiently—especially blue and green wavelengths, which travel farthest underwater.

The mirror system allows the spookfish to detect faint movements below it—like the flicker of a glowing jellyfish or the outline of a predator.

It’s a rare example of nature choosing mirrors over lenses… and succeeding.

Transparent Body, Invisible Fish

To make things even weirder, the spookfish has a mostly see-through body. Its skull is almost entirely transparent, making its eyes look like floating black balls inside a glass dome.

This helps it avoid detection. In a place where being seen means being eaten, invisibility is a powerful defense.

And with its mirror-eyes, the spookfish can spot predators and prey without being spotted itself.

Rarely Seen, Perfectly Designed

The spookfish lives at depths of 700 to 1,000 meters, which makes it almost impossible to observe in the wild. Most of what scientists know comes from deep-sea submersibles and rare specimens caught in research nets.

It was first discovered over a century ago, but its mirror eyes weren’t understood until 2009, when scientists used high-resolution imaging to finally confirm the structure.

Since then, the spookfish has become a legend among marine biologists—a symbol of just how weird and creative evolution can be.

Nature’s Optical Engineer

We often think of mirrors as human inventions. We use them in telescopes, cameras, satellites, and science labs.

But the spookfish had them millions of years ago.

Built entirely from natural materials, aligned with microscopic precision, and embedded inside a living eye, the spookfish’s mirror system is a biological marvel.

It doesn’t just prove that nature is smart. It proves that nature is sometimes way ahead of us.

So the next time you look in a mirror, remember: there’s a little fish floating in the dark somewhere, using mirrors better than we ever could.