Surprised: Fish that live in the dark ocean still see colors

Recent research by a team of scientists from the University of Queensland found that deep-sea fish can see colors in the dark, shedding light on visual evolution in vertebrates, including human. Dr. Fabio Cortest said vertebrates have two types of receptor cells - rod and cone - that allow organisms to see things around them.

Cones are utilized in strong light conditions while rod cells work in low light conditions. Both rod and cone cells have a light-sensitive protein - called opsin - that absorbs light at a certain wavelength, allowing visual sensitivity to a variety of colors. The team thinks that 99% of vertebrate animals have only one protein opsin in their rod cells, which makes them nearly color blind in low light conditions.

Artwork: Silver spinyfin fish.

Deep-sea fish live below the depth of 200 - 1500m is no exception. Scientists say that under such depths, the fish can only see monochromatic, particularly blue light. However, there are exceptions: When examining the genome of 101 fish species, scientists found 13 species that have more than one opsin protein in rod-shaped photocell cells.

Among the above rare cases, silver spinyfin fish has 38 opsin. When analyzing gene sequences, scientists discovered that silver spinyfin fish can absorb a wide range of wavelengths of light, indicating they can see many colors. The vision of this fish is thought to have evolved to become a survival weapon.

In order to survive with such depth, fish need to be able to see predators or potential prey because most of the light below that depth is bioluminescent. The bioluminescent ability emits colors in the deep seabed and the ability to see the multicolor will help the fish determine whether it is seeing predators or prey and thereby take appropriate action.