How do fish glow in the dark?

Marine biologist Helen Scales explains the science behind bioluminescent fish.

How do fish glow in the dark?

The anglerfish's light radiates from the end of a fishing-rod-like extension on its forehead © Reinhard Wirscher / ullstein bild / Getty 


All sorts of living creatures are bioluminescent – fungi, insects, corals, shrimp – but of the animals with backbones, it’s only fish that glow in the dark.

The deep sea in particular is full of fish that make their own light.

Fish use light to hunt for food, find mates, startle predators and hide in the twilight depths 1,000 metres down.

By covering their bellies in a blue glow, they match the weak light that trickles down from above and disguise their shadowy silhouettes from hunters deeper down.

Fish glow in two ways. About half of the 1,560 or so bioluminescing species use internal chemical reactions that involve a light-emitting molecule (known generically as luciferin), speeded up by an enzyme (known as luciferase).

Others enter into partnerships with glowing bacteria that they house in special organs, sometimes under their eyes (to see through the dark, like a pair of headlamps), or at the end of fishing lures that dangle in front of their gaping mouths, to coax other animals to within biting range.


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