The largest known glowing vertebrate is the kitefin shark, which grows to nearly 6 feet. Its blue-green belly light may help hide its shadow from animals below.
ILLUSTRATION · AIA nearly six-foot deep-sea shark called the kitefin is the largest vertebrate known to make its own light, glowing blue-green from its underside.
The kitefin shark, Dalatias licha, can grow to 180 centimeters, close to six feet. In a paper published in Frontiers in Marine Science in 2021, Jérôme Mallefet, Darren Stevens and Laurent Duchatelet described it as the largest known luminous vertebrate.
The team studied sharks caught in January 2020 on the Chatham Rise off New Zealand, together with two smaller lanternsharks, and documented light production in all three species. Luminous sharks produce blue-green light.
Why glow?
That question is still open for the kitefin. Glowing sharks appear to use light for several purposes, including counterillumination, in which light on the belly helps hide an animal's silhouette from below.
For the kitefin, the authors suggest counterillumination may be co-opted as camouflage for a predator. It is a proposed explanation, not a demonstrated one, and the paper raises it as a question for further study.
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