Swimming into the twilight zone: The wonders of the lantern fish 
By Jane Adey CA Source: CBC News 10/30/2021
Jane Adey
Way down in a spooky part of the ocean called the twilight zone lives the lantern fish.

Aptly named, this flashy fish emits its own light; lantern fish have organs on their bodies, called photophores, that produce a molecule called luciferin that, when combined with oxygen, makes a blue-green light. The same way fireflies glow on land, lantern fish can glow underwater, an effect called bioluminescence.

Lantern fish are mesopelagic, meaning they live between 200 and 1,000 below the water's surface. In this twilight zone, there's very little light — less than one per cent of the light at the water's surface — but not complete blackness.
 

But why do lantern fish light up? According to Maxime Geoffroy, a fisheries researcher scientist at the Marine Institute in St. John's, the reasons are not fully understood.

The fish might be communicating with each other to signal danger lurking in the depths, he said.

"We know they produce light when they are stressed. So that's one hint that it's probably a reaction to predation or to fear.… The bioluminescence is being used to camouflage so their predators have trouble seeing them," said Geoffroy.

 
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