The kitefin shark, a predator of the deep ocean, has now been confirmed as the world’s largest glowing vertebrate. This shark can grow up to six feet long and shines with a soft blue-green light, turning the dark sea into a glowing world.
The finding was published in 2021 in Frontiers in Marine Science after researchers studied live specimens caught during an expedition in 2020 near New Zealand’s Chatham Rise. This area lies in the twilight zone of the ocean, hundreds of meters below the surface, where sunlight cannot reach. It is a place where mystery rules, and light is created not by the sun but by life itself.
The shark’s light comes from special skin cells called photophores. Inside them are tiny cells known as photocytes, which can produce light between 455 and 486 nanometers. That light shines mostly from the shark’s belly and fins, creating a glowing figure in the darkness.
Many other glowing creatures, such as the kitefin shark, do not rely on bacteria or typical chemical reactions to glow. Instead, it has its own internal process, making it unique. Scientists still do not fully understand how it works, but they believe hormones might play a role.
When the shark was first observed glowing, the moment was so powerful that it brought strong emotions to the scientists. Lead researcher Jérôme Mallefet from Université Catholique de Louvain shared his reaction with National Geographic, “I nearly cried when I saw it. It was so exciting.” It was something so rare and extraordinary alive in front of human eyes.
The researchers believe the glow may serve many purposes, though no single answer has been confirmed. It may act as camouflage, helping the shark blend with the faint light from above, making it harder for predators to spot. It could also help the shark in hunting, revealing or attracting prey in the dark waters. Another possibility is that the glow may allow sharks to communicate with each other.
The kitefin shark was not the only glowing creature studied. Alongside it, scientists documented two smaller species, the blackbelly lanternshark and the southern lanternshark. Though smaller, they too shined in the same soft blue-green light. Together, the three glowing sharks offered proof that bioluminescence is more common in deep-sea sharks than previously believed.
The twilight zone of the ocean, also known as the mesopelagic zone, ranges from 200 to 1,000 meters below the surface. It is one of the least explored places on Earth. Sunlight cannot reach, and darkness dominates.
Countless animals produce their own light, a natural gift called bioluminescence. From jellyfish to squid to fish, glowing creatures live there in large numbers. The kitefin shark now stands as the largest glowing vertebrate discovered so far.
Bioluminescence usually happens through a chemical reaction involving oxygen and compounds called luciferins, which are activated by an enzyme called luciferase. In some animals, glowing is caused by bioluminescent bacteria that live inside their bodies. But the sharks studied showed no signs of bacteria or luciferins. This means they glow through a different process, one still not fully explained by science.
The study authors explained the importance of this discovery in their report. “Bioluminescence has often been seen as a spectacular yet uncommon event at sea, but considering the vastness of the deep sea and the occurrence of luminous organisms in this zone, it is now more and more obvious that producing light at depth must play an important role in structuring the biggest ecosystem on our planet.”
The researchers explained that this is the first experimental study of glowing sharks from New Zealand, and they believe these findings give valuable insight into how sharks and other deep-sea animals survive in extreme environments where light does not exist naturally.
