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.
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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.
A close look at marine marvels
The ocean is truly home to some of the most amazing creatures, such as species recently discovered under Antarctica. Here's a selection of the world's most interesting aquatic animals.
Image: British Antarctic Survey/dpa/picture alliance
Unknown life
Under permanent ice cover that is hundreds of meters thick in Antarctica, researchers have discovered sessile animals (similar to sponges) that have adapted to extreme conditions like darkness and subzero temperatures, as well as being under such expanses of ice that these organisms are 260 kilometers (155 miles) from the open sea. To what species the rock-bound creatures belong remains unclear.
Image: British Antarctic Survey/dpa/picture alliance
Water dragon
It looks like a seahorse — but it's a red sea dragon, a rare marine fish. Researchers off the coast of Western Australia have only recently been able to admire these live specimens, which were identified in 2015. The animals were observed feeding at a depth of 50 meters (165 feet).
Image: picture-alliance/dpa/Scripps Oceanography/UC San Diego
Seahorses
The "real" seahorses are also quite unusual. They are one of the few species to swim vertically. But this doesn't work out too well, so they are just poor swimmers. The males carry fertilized eggs and give birth to their young.
Image: picture-alliance/ dpa
Electric eels
Despite its name, an electric eel is not an eel but a knife fish. It is indeed electric, though, and generates powerful electric shocks of up to 600 volts to kill prey. Researchers have learned that the fish also uses its high-voltage discharge as a high-precision tracking device — similar to the echolocation calls of bats.
Image: imago/Olaf Wagner
Banded archerfish
Banded archerfish live in brackish water and have come up with a unique way to kill prey: They spit a jet of water into the air to shoot down insects. Larger fish may even hit targets up to 3 meters away.
This fish buries itself in the sand and waits till its prey passes its head. Then it shoots upward and gets its meal. Stargazers have top-mounted eyes and a large, upward-facing mouth. If you ever see one, be careful: The species is venomous.
Image: picture-alliance / OKAPIA KG
Stonefish
Venomous and good at hiding? The stonefish is both! The species looks exactly like a stone overgrown with algae. But step on it and you will come to know its needlelike venomous spines. It can even be fatal for humans.
Image: gemeinfrei
Puffer fish
Puffer fish have an elastic stomach that they can fill with water when feeling threatened. This way they become much larger and almost spherical in shape. They produce the tetrodotoxin, which can kill humans. In Japan, people eat puffer fish.
Image: picture alliance/Arco Images
Anglerfish
An anglerfish attracts its prey with an illicium, or a fleshy growth from its head. The tip of the illicium illuminates to make prey curious — and then they are swallowed up by the huge mouth of the predator. Anglerfish can be found almost anywhere in the world, including the deep sea.
Image: Flickr/Stephen Childs
Viperfish
With high pressure, almost no light and little food, animals have to be especially adapted to be able to live in the deep sea. Viperfish need to make absolutely sure that they don't miss a meal — that's what the huge mouth and the sharp teeth are for.
Image: picture-alliance/dpa
Plaice
The plaice is a flatfish — no doubt about that. The well-camouflaged fish bury themselves in the sediment. They develop so that both eyes end up on the same side of the head.
Image: picture-alliance/dpa/H.Bäsemann
Mudskippers
Mudskippers apparently couldn't decide whether they liked land or water more. So they compromised and chose intertidal habitats. They are definitely fish but can use their pectoral fins to walk on land. They can breathe through their skin like amphibians.
Image: picture-alliance/dpa/MAXPPP
Hammerhead shark
Researchers believe that the flat, sideways extended head gives hammerhead sharks a higher visual field. That helps them find their prey.