The Fish that Sees Red

Steve Jenkins

Making Sense of the Natural World

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     Have you ever noticed how photographs of underwater scenes have a bluish tint? Sunlight is made up of a rainbow of colors, but when it enters the water the reds and yellows in the light are quickly filtered out. The blues and greens penetrate deeper into the water and give those watery scenes their peculiar cast. Because there is very little red light in the deep sea, most of the animals that live there have never evolved the ability to see the color red. This is why many deep-sea animals are red. In the depths of the ocean, a creature that can’t be seen is safe from many predators.

     There is an unusual fish that takes advantage of its fellow sea creatures’ colorblindness. The stoplight loosejaw, a member of the dragonfish family, can see the color red. Not only that, but it has a patch on its face that glows red. It also has a glowing green spot on its face, which is probably used to communicate with other dragonfish. These red and green patches explain the “stoplight” part of this fish’s name. The “loosejaw” comes from this fish’s ability to open its mouth extra wide and swallow large prey. Scientists think that the open structure of the lower jaw allows the fish to close its mouth quickly, making it difficult for prey to escape. Relative to its size, the stoplight loosejaw has one of the widest gapes of any fish, with a lower jaw measuring one-quarter of the fish’s length. It’s not easy for animals that live in the dark waters of the deep sea to find prey. Many of them, including the stoplight loosejaw, have large mouths and sharp fangs that help ensure that their prey cannot escape.
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     Below about 650 feet (200 meters), very little sunlight penetrates the ocean. Below 3,300 feet (1,000 meters), the only light is that produced by living creatures. Almost all deep-sea creatures can bioluminescence, or make their own light. But the light they produce is usually blue or green. When the stoplight loosejaw switches on its red spotlight, other creatures in the water are illuminated. Being blind to the color red, they don’t realize that they’ve been spotted. Dragonfish are not known as picky eaters. If one of the lit-up animals is a fish, shrimp, or other suitable prey, the stoplight loosejaw quickly grabs it and swallows it.

The stoplight loosejaw's attributes include a red spot, hinged jaws, and needle-like teeth.  Illustration by Steve Jenkins

 There are two kinds of stoplight loosejaws. The Northern (Malacosteus niger) shown here and the Southern. Together they are found everywhere in the world except the North and South Poles.  Wikimedia Commons

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Steve Jenkins has written and illustrated more than forty
nonfiction picture books, including the Caldecott Honor–
winning What Do You Do with a Tail Like This? and the
Boston Globe Horn Book honor–winning The Animal Book.
His most recent books are Apex Predators: Top Killers Past
and Present and Who Am I?, an animal guessing game
written with Robin Page.

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​MLA 8 Citation
Jenkins, Steve. "The Fish That Sees Red." Nonfiction Minute, iNK Think Tank, 6
     June 2018, www.nonfictionminute.org/the-nonfiction-minute/
     The-Fish-that-Sees-Red.