Some deep-sea fish can see colors in the dark

The bottom of the ocean is dark. Like, really dark. So dark that some marine species have evolved ways of life that don't depend on light. There are microorganisms that live off of heat vents at the ocean floor, creatures that produce their own light in a phenomenon known as bioluminescence — and now, new research has found, fish that can see color even in the dark.

Until now, we've thought that all vision works more or less the same way: The cones in any animal's eye may allow for color vision in light, but vision in darkness is regulated by the rods in the eye, which means it's all monochrome. But a new study published in Science on Thursday found several species of deep-sea fish that have additional rods in their eyes, allowing for multicolored vision in darkness.

Even more interesting is the fact that not all of this type of vision seems to have come from the same place. Rather, there's evidence that it evolved "several times independently of each other," explained study co-author Walter Salzburger. This is a good sign that it's genuinely useful for deep-sea fish to "detect bioluminescent signals," he explained.

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This newly discovered dark-vision may enable the fish that use it to see some colors at depths of up to 5,000 feet below sea level, Gizmodo reports. Light from the surface world can barely reach that deep, so it's impressive that anything can see at all down there, rather than relying on other senses to detect surroundings. Further research will be needed in order to determine exactly what deep-sea fish are using this extraordinary capability for, but it's clearly an advantage down in the depths. Learn more at Gizmodo.