A glowing swell shark. © David Gruber / iScience

Light shed on secrets of glow-in-the-dark sharks

While we know how corals and jellyfish can fluoresce, researchers haven’t figured out exactly how sharks can do it – until now.

Scientists have deciphered the secret of how glow-in-the-dark sharks light up in the ocean depths.

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While researchers have known for a while that invertebrates such as corals and jellyfish can fluoresce thanks to special proteins in their bodies, they haven’t figured out exactly how sharks can do it – until now.

Researchers from City University of New York and Yale University studied two species of sharks, called swell sharks and chain catsharks. Both of these sharks can live at depths of greater than 450 metres, where they fluoresce with a bright green colour. The scientists removed samples of chemicals from the sharks’ skin, and found that the lighter-coloured areas of skin contained a new type of fluorescent molecule previously unknown to science.

As well as allowing the sharks to glow and therefore recognise each other in the ocean, the fluorescent molecule may even help to protect the animals against infections, thanks to its antibacterial properties.

“Studying biofluorescence in the ocean is like a constantly evolving mystery novel, with new clues being provided as we move the research forward,” said Prof David Gruber. “After we first reported that swell sharks were biofluorescent, my collaborators and I decided to dive deeper into this topic. We wanted to learn more about what their biofluorescence might mean to them.”

There has been a huge surge of interest in studying fluorescent animals, as if we can harness their abilities then it could help us develop new imaging systems for use in science and medicine.

“Sharks are wonderful animals that have been around for over 400 million years. Sharks continually fascinate humans, and they hold so many mysteries and superpowers,” Gruber said. “This study highlights yet another mystery of sharks, and it is my hope that this inspires us to learn more about their secrets and work to better protect them.”


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