A Glow-in-the-Dark World Beneath the Sea

Who's the brightest of them all? Ocean dwellers in the know will tell you it's the many species of "glow-in-the-dark" fish that inhabit the deepest depths of the ocean. Most fish that live in the deepest depths are able to give off their own glow, a process called bioluminescence. In fact, in the sea, bioluminescence is everywhere – in fish, sea slugs, squid, jellyfish and many other deep-sea dwellers.

What is Bioluminescence?

Bioluminescence is a glow that is the result of a chemical reaction within the tissues. This reaction takes place when a special enzyme and a special protein inside the cells are exposed to oxygen and water at a temperature of about 75 degrees Fahrenheit (25 degrees Celsius). The result is energy that gives off light and creates patches of bioluminescent tissue, photophores, which are kidney-shaped organs arranged in distinct groups on the organism. It's the same process that causes a firefly to light up in the summer night.

Almost all of marine bioluminescence are blue in color. There are two reasons for this: First, blue-green light travels furthest in the water. Second, most organisms are sensitive only to blue light – they lack visual ability to absorb longer red or shorter ultraviolet light.

Survival Tricks

Photophores help fish survive in the deep sea in three ways:

The female angler fish eats fish and shrimp that are attracted by what looks like a fishing rod growing out of the top of her head with a light at the end. She also attracts prey by vibrating the lure. This is much like the use of colorful lure by fishermen.