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Global Ideas

Hunting with a flashlight

The splitfin flashlight fish has a built-in light that it can turn into its very own stroboscope. Now researchers may have figured out what they use it for.

If you hunt in the dark, it helps to carry a flashlight. At least that seems to be true of the aptly named splitfin flashlight fish.

The animals, which live in the Pacific Ocean, have light organs located underneath their eyes, which the fish can turn on and off, as if blinking.

So how do you get a built-in flashlight like this? The flashlight fish have pouches under their eyes, which contain bioluminescent bacteria - their natural light bulbs, so to speak.

The fish can roll the pouches back, covering up the light source - allowing them to turn the light on and off.

This process can also be quite rapid. At night, the fish usually crank up their natural stroboscopes to about 90 blinks per minute. Pretty flashy - but what's the point of these disco lights? Researchers from Ruhr-University in Germany think they may have an idea.

"The splitfin flashlight fish use bioluminescent light to detect planktonic prey during the night and adjust the blink frequency in a context-dependent manner," says Jens Hellinger, chair of the Department of Zoology and Neurobiology at Ruhr-University Bochum.

The researchers studied a swarm of splitfin flashlight fish in a coral reef aquarium, and found that the frequency of blinks decreased from around 90 to around 18 per minute when the fish detected prey. For that, they also kept the lights on for longer. The scientists suspect that they do so to be able to better detect prey.

Since Hellinger's team, which published its findings in the current issue of the journal PLOS One, conducted its investigation in a fish tank, the researchers recommend that the phenomenon should be reexamined in the wild to confirm that the fish display the same behavior under natural conditions.

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