Scientists previously believed that the deeper a fish lives, the less complex their visual system would be. But according to a new study published on 9 May in Science, this may not be so accurate.

The study shows that deep-sea fish species living in the near-total darkness have evolved highly-sensitive vision.

The research team led by Walter Salzburger and Zuzana Musilova from the University of Basel in Switzerland has identified a previously undocumented visual system in deep-sea fish

The fish endowed with this highly sensitive form of vision, of which 13 species are now known, may discern certain wavelengths of color at depths reaching 1,500 meters (5000 feet), where light from the surface is practically non-existent.

Deep-sea creatures have certainly adapted in many ways to the dark ocean environment, including increased eye or pupil sizes, extremely telescopic-shaped eyes, and modifications to the microscopic retina structure itself. But some deep-sea fish are also equipped with a series of distinct rod opsin photopigments, according to the new study.

These rod opsins allow the fish to hone in on a wide range of visual wavelengths—namely the wavelengths produced by bioluminescent deep-sea organisms. Opsins are proteins capable of absorbing light.

“This is the first paper that examines a diverse set of fishes and finds how versatile and variable their visual systems can be,”

“The genes that determine the spectrum of light our eyes are sensitive to turn out to be a much more variable set of genes, causing greater visual system evolution much more quickly than we anticipated.”

– Karen Carleton, a biology professor at the University of Maryland and co-author of the paper.

Reference:

Musilova et al. “Vision using multiple distinct rod opsins in deep-sea fishes“. Science, 2019. Doi/10.1126/science.aav4632