Scientists have discovered that many shark species, living secretively in the dark depths of the ocean, actually glow to become more visible to each other, and presumably to make it easier to find a mate. The latest documentation of biofluorescence in marine life came in a 2016 study of two species, the chain catshark and the swell shark. Both are small fish -- about three feet (.9 m) long -- that hide in crevices at depths of 1,600 to 2,000 feet (488 to 610 m).
In the case of the swell shark, this biofluorescence is bright green and is produced by fluorescent proteins inside its skin. Humans can’t see it, but other sharks can, thanks to a higher density of light-sensitive cells in their retinas.
Finding biofluorescence in the sea:
- Biofluorescence in fish is a relatively new discovery by scientists, who now believe that it occurs in more than 200 species of sharks and bony fish, as well as marine turtles, eels, and jellyfish.
- To see the fluorescent markings, shark researchers used cameras with yellow filters to block out the natural blue light, the same way a shark’s eye does.
- Biofluorescence has been used by medical researchers to track how cells work, leading to medical advances in the study of AIDS, cancer and Alzheimer's disease.