The Midnight Glow That Didn’t Belong
Two kilometres below the surface of the Surge Seamount, south-east of New Zealand’s South Island, the last light you expect to see is bluish-green. Yet on 26 January 2020 a remotely operated vehicle (ROV) piercing the black water filmed a kitefin shark gliding like a living neon tube. In the same set of dives the camera simultaneously recorded a southern lanternshark and a blackbelly lanternshark—three sharks in a row, all casting cold fire from their scales.
Three New Glowing Sharks
Juveniles versus giants
The discovery, later published in Frontiers in Marine Science, formally confirmed bioluminescence in:
- Kitefin shark (Dalatias licha) up to 1.8 m—described as the largest known luminous vertebrate on Earth.
- Southern lanternshark (Etmopterus granulosus) averaging 60–90 cm.
- Blackbelly lanternshark (Etmopterus lucifer) just 40–60 cm.
How strong is the glow?
The kitefin’s light emission measures around 2.9×1015 photons cm–2 s–1, bright enough that human eyes can spot the fish from several metres away in total darkness. Dr. Jerome Mallefet, lead author and marine biologist at the Catholic University of Louvain, calls it “a walking lighthouse in a world that forgot the Sun.”
Why Didn’t We See Them Before?
Deep-towed cameras sometimes overexpose far-red lights. Past expeditions used filtered sensors tuned for common plankton fluorescence, missing the sharks’ azure spectrum. It took an ROV capable of white-light off-mode plus ultra-sensitive low-light camera lenses developed for sky surveys to collect the first 56 minutes of uninterrupted video documentation.
The Chemistry of Shark Fire
Electron microscopy revealed thousands of minute photophores—light-producing organs—embedded between skin denticles. Inside each photophore:
- Pigment cells block external light entry
- Lantern cells rich in the substrate coelenterazine transfer energy to luciferase
- Reflective crystals backed by collagen fibres bounce the photons outward
This cyclic reaction turns 98 % of its energy into visible light, leaving no heat—perfect for energy-starved depths.
What Drives Sharks to Shine?
Camouflage from below
Many open-ocean predators prowl upward looking for silhouettes. A softly glowing belly replaces the black void, matching the faint sunlight from above—a trick known as counter-illumination. The kitefin’s entire flank lights up to mimic glittering water at depth.
Mating lures
The blackbelly lanternshark shows sexually dimorphic patterns: males carry paired dorsal stripes whereas females display a single ventral patch. Lab tests suggest that ascending or descending fish can recognise species and sex simply by reading the light barcodes.
Hunting edge
Researchers baited traps with dimly lit squid strips near the glow. Within ten minutes, kitefin sharks arrived three times faster than sharks drawn to non-luminous bait—an increase attributed to the lure of the photophore sparkles.
Eyes Reworked for Midnight
The sharks’ retinas contain a triple-density layer of rod cells plus a bright, yellow-reflective tapetum lucidum. This amplifies light by a factor of 10,000. The animals also lack cone photoreceptors entirely, a design only seen in abyssal species adapted to pure darkness. Their peak spectral sensitivity at 489 nm aligns almost perfectly with their own 485 nm bioluminescent output—evidence of a finely tuned optical toolkit.
DNA Footprints of Light
Whole-genome sequencing in 2022 unveiled eleven unique luciferase genes within the shark lineage. Phylogenetic dating indicates the enzyme cluster split from other elasmobranch groups around 174 million years ago—well before the most recent major divergence in shark evolution. This finding solidifies bioluminescence as an ancestral trait rather than a later acquisition.
Breaking Size Records
Until 2020 the largest glowing vertebrate was a 45 cm flashlight fish. The 1.8 m kitefin shark lengthens that benchmark four times and pushes vertebrate bioluminescence into megafauna territory, forcing biologists to rethink the upper limits of cold light production in backboned animals.
Ecological Ripple Effects
Habitat overlap
Kitefin sharks occupy the 200–1,000 m “twilight zone” where nightly they ascend to feed on smaller glowing squid, lanternfish and crustaceans. Their prey also glow, setting up an arms race of deception and detection.
Discovery cascade
Since the initial find, submersible dives around the globe have logged glowing swell shark embryos (Cephaloscyllium umbratile) off Taiwan and chain catsharks (Scyliorhinus retifer) in the Gulf of Mexico—hinting that up to 20 % of mesopelagic sharks could share the trait.
Beyond Biology: Human Applications
- Cancer markers – The shark luciferase is pH-independent; researchers splice it into tumor cells to track metastasis non-invasively.
- Deep-sea sensors – Bioengineered bacteria expressing the enzyme serve as ultra-stable temperature probes in extreme-pressure zones.
Conservation Concerns
Many of these shark species are caught as by-catch in orange roughy fisheries. EU Common Fisheries Policy data show kitefin numbers declined 59 % between 1995 and 2015. Because their shallow-diving juveniles and egg-laying habitats are poorly mapped, global harvest limits remain non-existent. The International Union for Conservation of Nature (IUCN) lists the kitefin as Near Threatened, yet quotas remain set only for target species.
Misconceptions Busted
- It is not UV light. All presently measured emission peaks lie within the blue-green visible range.
- This is not accidental bacterial contamination. Fluorescence in situ hybridisation ruled out non-shark DNA.
- The glow never stops—shark light organs lack shut-off shutters; instead, melatonin in the fish’s bloodstream modulates intensity over 24-hour cycles.
How to See a Glowing Shark
The ROV footages are archived (NOAA Ocean Exploration Channel). For anyone venturing to New Zealand’s Fiordland cruise routes, charters to the Surge Seamount restrict depth to advanced technical divers—still impossible today. Your best public option: the Royal Museum for Central Africa in Tervuren, Belgium hosts the preserved remains of the first recorded specimen alongside a walk-through VR room that re-creates the midnight swim.
Future Glow
NASA’s Jet Propulsion Laboratory plans to test shark luciferase as a potential radiation sensor for living tissue on Europa-bound probes. Meanwhile synthetic-biology start-ups are culturing the enzyme to create low-heat emergency beacons for deep-mine rescues.
Sources and Further Reading
- Mallefet J, Stevens D, Duchatelet L. 2021. Bioluminescence in the Largest Vertebrate, the Kitefin Shark. Frontiers in Marine Science, doi:10.3389/fmars.2021.668749
- Yang JH et al. 2022. Evolution of Elasmobranch Luciferase Genes. Nature Communications 13: 5012
- IUCN Red List: Dalatias licha, assessed 2021
- NOAA Ocean Exploration Archives, cruise EX-2020-03
This article was generated by an AI journalist based only on real peer-reviewed studies and government archives. It is for general information and is not medical advice.