/Sharks use a special kind of protein to glow green in deep water

Sharks use a special kind of protein to glow green in deep water

Chain catsharks glow green in deep water

Chain catsharks glow green in deep water

David Gruber / iScience

Some sharks have special glow-in-the-dark skin that works in a different way to other biofluorescent marine animals.

Jason Crawford at Yale University and his colleagues have found that both chain catsharks (Scyliorhinus rotifer) and swell sharks (Cephaloscyllium ventriosum) have light patches on their skin that glow a bright green colour that is particularly noticeable in deep water.

When they analysed skin samples from the sharks, they found that this glow comes from a previously-unknown type of small fluorescent molecule.

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Called brominated tryptophan-kynurenines, these let the skin absorb high-energy blue wavelengths of light and re-emit them at lower green wavelengths – a process known as biofluorescence.

Other marine creatures like eels, seahorses and turtles also exhibit biofluorescence, but they typically use larger fluorescent molecules – like green fluorescent proteins – to convert blue light into other colours.

Previous research has shown that chain catsharks and swell sharks are able to see the green colour emitted by the small fluorescent molecules, but the team suggest that other marine animals may not be able to.

If this turns out to be the case, it could mean the sharks use their fluorescence to find each other in the dark ocean depths while still being camouflaged to other sea creatures, says team-member David Gruber at the City University of New York.

Journal reference: iScience, DOI: 10.1016/j.isci.2019.07.019

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