A fluorescent protein has been spotted in a fresh water eel. It is the first ever found naturally occurring vertebrate. The protein is common on sushi menus but is becoming difficult to find in the wild.

Anguilla japonica is also called as unagi and it is born in the sea. The eggs and larvae are carried to Japan, China, Taiwan, Korea, and Vietnam through rivers, lakes, and estuaries. Scientists at Japan's RIKEN Brain Science Institute have found glow-in-the-dark protein in the muscles of the carnivorous fish.

The study was published in the scientific journal Cell. The researchers believe that species migration is aided by the glowing protein. The researchers found that it glowed only when activated by a chemical. The chemical is called bilirubin, which is a breakdown product of molecules found in blood.

Bioluminescence is known as the production and emission of light by a living organism. It is found in many microbes, plants and animals. Anglerfish is known to use glowing bacteria to cast light underwater. Chemical reactions help lanternfish to emit light.

The discovery unraveled the mystery behind the green light emitting ability of eels. According to researchers, fluorescent proteins are present naturally in some species of jelly fish.