How These Fishes Can See Color In The Light-less Depths Of The Ocean


A deep-sea anglerfish living within the pillow basalts. You can see its round lure in between its two eyes. This fish is an ambush predator that waits for prey to be attracted by the lure before rapidly capturing them in one gulp with their large mouths.
Seen during the first leg of the 2016 Deepwater Exploration of the Marianas expedition.


Light does not travel very far in the ocean – the average depth of the world’s oceans is approximately 12,000 feet and it is 36,200 feet below sea level at its greatest depth. Sunlight can reach some 3,280 feet below sea level but generally does not extend more than 650 feet.  Nevertheless, deep-sea fish do have the ability to see, although fishes in the deep ocean were traditionally considered to have simpler vision systems. Now, new research shows that several species of deep-sea fish have highly unique vision systems that allow them to see flashes of light that many organisms naturally produce (“bioluminescence“).

“They have more sensitive eyes and can see way better than humans in lower light,” says lead author Dr. Zuzana Musilová, a researcher and lecturer at the University of Basel in Switzerland.

In this study, scientists examined the genes of 101 deep-sea fish that spanned 26 different species and found that they carried more genes for rod opsin than the researchers expected. Opsins are light-sensitive proteins in the retina of the eye that help convert light into an electrochemical signal that the brain can interpret. And, rod opsins are specifically used in environments with stable temperatures and low light. However, where humans only have a single rod opsin gene, the researchers found that a fish that lives at depths greater than 6,000 feet, the silver spinyfin, has 38 rod opsin genes. Overall, half of the species in this study had more than one opsin gene.

“We believe they can detect more shades of blue and green than us,” Musilová says.

These additional genes increase the fishes’ sensitivity to different colored lights, which may be able to help them differentiate whether a bioluminescent flash comes from a predator or prey.

According to co-author Dr. Fabio Cortesi, a postdoctoral researcher at Australia’s Queensland Brain Institute, “Understanding how these visual systems work, how sensitive they are and how they allow these critters to survive in their extreme environment provides a treasure of knowledge that might be useful for future applications, such as in visual sensor design, camera designs or remote sensing.”

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