Flashlight Fish Wear Glow-in-the-Dark Bacteria Eyeliner

Many people just found out that flashlight fish exist, thanks to the viral tweet below. The glowing fish have lights under their eyes that blink on and off. But it turns out that there’s even more weird stuff to learn about them. The light organs below their eyes are filled with a symbiotic bioluminescent bacteria that can glow different colors. Scientists still research how and why flashlight fish use this light to eat, mate, and escape predators.

There are actually multiple species of flashlight fish found around the world and their light organs all work a bit differently. Some species turn the light on and off by blinking an eyelid-like membrane over it. Others cover the light by rotating their light organ into a dark pouch.

Flashlight fish favor dark environments like caves and overhangs. In those conditions, they end up looking like a pair of spooky glowing eyes with no body, as in the video above. It makes sense that their prey, tiny plankton, would be attracted to the light and come in for a closer look.

In regular daylight, they look like a basic black and grey fish with a normal round eye. But even in semi-dark conditions like the video above, the large bean-shaped light begins to glow. They take on a much more alien-like form.

Flashlight fish, a black fish with a light organ under its eye in both light (left) and dark (right) conditions
Tropical Marine Center/ Toledo Zoo

We’ll go ahead and add the flashlight fishes to the long and ever-growing list of weird ocean animals we’ve learned about. There’s also the jawless hagfish that release slime to escape predators, blind cave-dwelling fish that “speak” with regional accents, and of course the barreleye fish and its translucent head. So why not a fish with a blinking light that’s actually a symbiotic relationship that we don’t entirely understand? That seems almost normal in comparison.

Melissa is Nerdist’s science & technology staff writer. She also moderates “science of” panels at conventions and co-hosts Star Warsologies, a podcast about science and Star Wars. Follow her on Twitter @melissatruth. 

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