The ocean never ceases to amaze me in its contribution to the development of vision. From the scallops with more than 200 eyes, we now go to this fish.
Most of us can’t see in the dark. In the pitch black darkness, we get robbed of our vision and we are left to rely on our other senses in order for us to feel the environment. Such is the case for the ancestors of the cave fish and crickets when they moved into pitch black caverns. However, this is not the case for fishes living in the great depths of the sea, who can still see well despite the absence of sunlight. An example of this is the image above — the spinyfish, who can still see clearly at the depth of 2000 meters. Their secret? They have had “an extraordinary increase in the number of genes for rod opsins, retinal proteins that detect dim light.”
The finding "really shakes up the dogma of deep-sea vision," says Megan Porter, an evolutionary biologist studying vision at the University of Hawaii in Honolulu who was not involved in the work. Researchers had observed that the deeper a fish lives, the simpler its visual system is, a trend they assumed would continue to the bottom. "That [the deepest dwellers] have all these opsins means there's a lot more complexity in the interplay between light and evolution in the deep sea than we realized," Porter says.
At a depth of 1000 meters, the last glimmer of sunlight is gone. But over the past 15 years, researchers have realized that the depths are pervaded by a faint bioluminescence from flashing shrimp, octopus, bacteria, and even fish. Most vertebrate eyes could barely detect this subtle shimmer. To learn how fish can see it, a team led by evolutionary biologist Walter Salzburger from the University of Basel in Switzerland studied deep-sea fishes' opsin proteins. Variation in the opsins' amino acid sequences changes the wavelength of light detected, so multiple opsins make color vision possible. One opsin, RH1, works well in low light. Found in the eye's rod cells, it enables humans to see in the dark—but only in black and white.
More information of this amazing discovery at the Science Magazine.
(Image Credit: Pavel Riha/ University of South Bohemia)