Scientists have discovered that certain species of shark can turn fluorescent green using ocean’s blue light.
Some sharks take on the glowing colour as a form of disguise to make sure only their own kind can identify them.
Researchers also say it could help the sharks fight off infections.
A new study has identified what lies behind the colourful transformation – a family of small-molecule metabolites.
Published in the iScience journal, the research focused on two species of sharks – the swell shark and the chain catshark.
David Gruber, professor at City University of New York and lead author of the study, said: “The exciting part of this study is the description of an entirely new form of marine biofluorescence from sharks – one that is based on brominated tryptophan-kynurenine small-molecule metabolites.”
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These types of small-molecule metabolites are known to be fluorescent and activate pathways similar to those that, in other vertebrates, play a role in the central nervous system and immune system.
Co-author Jason Crawford said: “It’s a completely different system for them to see each other that other animals cannot necessarily tap into.
“They have a completely different view of the world that they’re in because of these biofluorescent properties that their skin exhibits and that their eyes can detect.
“Imagine if I were bright green, but only you could see me as being bright green, but others could not.”
Professor Gruber added: “It is also interesting that these biofluorescent molecules display antimicrobial properties.
“These catsharks live on the ocean bottom, yet we don’t see any biofouling or growth, so this could help explain yet another amazing feature of shark skin.
“This study opens new questions related to potential function of biofluorescence in central nervous system signalling, resilience to microbial infections, and photoprotection.”
Researchers noticed that the sharks’ skin had two light and dark tones – light and dark – and extracted chemicals from the two skin types for analysis.