Fish living in the deep ocean have evolved highly-sensitive eyes that can see a range of colour hues in the near-darkness.
â€śItâ€™s a big surprise,â€ť says Zuzana Musilova at the University of Basel in Switzerland. â€śThey have more sensitive eyes and can see way better than humans in lower light.â€ť
Musilova and her colleagues collected DNA from 26 species of fish that live more than 200 metres below sea-level. Analysing this DNA, the team found that six species carried additional genes for rod opsin â€“ the light-sensitive protein that enables the retinaâ€™s rod cells to detect light.
Vertebrate animals use rod opsin to detect light in dim environments, but most species â€“ including humans â€“ only have one rod opsin gene. However, adult silver spiny fins (Diretmus argenteus) â€“ a flat fish that lives at depths down to 2,000 metersâ€” has 38 of them.
The team translated these genes into proteins in a dish and shone lights of different wavelengths onto them, to see how theyâ€™d respond. They found that that these opsins detect a wide range of colours, and are especially sensitive to green and blue light.
â€śWe believe they can detect more shades of blue and green than us,â€ť Musilova says.
Musilova says having highly sensitive eyes may be useful for detecting the glowing bioluminescence emitted by many deep-sea creatures.
These bioluminescent lights are mostly blue and green in colour. Being able to tell colours apart could help fish distinguish whether a flash comes a predator or prey, Musilova says.
Journal reference: Science, DOI: 10.1126/science.aav4632
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