Largest bioluminescent vertebrate

The world's largest bioluminescent vertebrate is the kitefin shark (Dalatias licha), a deepsea species that can attain a known total length of up to 1.8 m (5 ft 11 in). It lives at depths of 200–600 m (650–1,970 ft), usually close to the seafloor, and is found in waters globally, including those off New Zealand's eastern coast, where specimens collected in January 2020 were found to bioluminesce – the first time that this phenomenon had been recorded from this particular shark species. Both its ventral surface and its two dorsal fins were found to glow, with fainter glowing occurring laterally and dorsally generally too, but the purpose served by such activity is as yet undetermined. The findings were documented in the journal Frontiers in Marine Science in February 2021.

The emitted light is blue-green in colour, with a wavelength of 455–486 nanometres, and its emission, from specialized skin cells called photocytes, is hormonally controlled, being triggered by melatonin.

Although it is the largest vertebrate to exhibit bioluminescence, the kitefin shark is not the largest vertebrate to glow. That honour belongs to another shark species, but a much bigger one, the whale shark (Rhincodon typus), which can attain a confirmed total length of up to 18.8 m and is the world's largest fish. Its upper surface is patterned with numerous small white spots that glow brightly in the dark, not through bioluinescence but rather via biofluorescence, in which an animal absorbs wavelengths of light invisible to the human eye and re-emits them at longer wavelengths that are visible.