There is near-total darkness at the bottom of the ocean, but some deep-sea fish species have found a way to adjust with superpowered vision.
Seeing Color In Darkness
New research, published in the journal Science, reveals that certain deep-sea fish species can detect different wavelengths of light even in the low-light conditions near the bottom of the ocean. It gives them color vision that is absent in many fishes in the near-total darkness of the deep sea.
Findings show that these particular species are equipped with additional rhodopsin genes for photopigments with rod opsin, a light-sensitive protein that reacts to a specific wavelength of light.
Color vision is achieved with the interaction of different opsins that react to different wavelengths of light; cone opsins in bright light and rod opsins in darkness. Since many vertebrates only have a single rod opsin, most of them are color blind at night.
By studying the genomes of more than 100 different fish species, the scientists were able to identify 38 different rhodopsin genes. The opsins can detect a wide spectrum of hues, but are particular sensitive to blue and green.
Among the genomes of the team analyzed, 13 species feature multiple rod opsins with the silver spinyfin (Diretmus argenteus) having the most rod opsin genes at 38. This means that this particular fish can likely see a variety of colors in near-total darkness.
Other types of fish that's been found with additional rod opsins include the lanternfish, tub-eye fish, and viperfish.
"It's a big surprise," Zuzana Musilova, study author from the University of Basel, said. "They have more sensitive eyes and can see way better than humans in lower light."
An Evolutionary Advantage In Deep Sea Conditions
The superpower is incredibly useful in the deep sea's low-light conditions, especially considering there are plenty of bioluminescent organisms in those depths that can be either predator or prey.
With computer simulations and laboratory experiments on the proteins, the researchers found that each rod opsin detects a certain wavelength of light. These genes cover the entire wavelength range of light that bioluminescent organisms produce in the deep sea.
"It appears that deep-sea fish have developed this multiple rhodopsin-based vision several times independently of each other, and that this is specifically used to detect bioluminescent signals," explained Walter Salzburger from the University of Basel, adding that this gives deep-sea fish an evolutionary advantage as they can see potential prey or predators much better.