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Answer by Leah Alissa Bayer:
As weird as it may sound, yes, fish get sunburns.
Koi kept in ponds are particularly susceptible to sunburns, as are fish in outdoor farming facilities where overcrowding forces fish to the surface. The combination of shallow, clear water and lack of natural shading devices leaves these guys vulnerable to intense UV penetration, causing skin sores. The burns can be fatal if left untreated and unprotected.
In natural settings fish are less likely to get burned for a multitude of reasons. For one, water is usually deeper. It also does a better job at obscuring rays; turbidity from suspended solids, or discoloration from dissolved organic substances, usually provides an excellent barrier against all UV wavelengths.
And some fish actually produce their own natural sunscreen to combat the summer rays. Researchers from Oregon State University discovered that fish naturally produce the compound gadusol, which provides UV-B protection among many other things. We’ve known that bacteria, algae, and fungi produce gadusol and thought fish obtained the compound by eating the microorganisms that made it. But as a result of the study we now know they synthesize the compound on their own. So of course, as we humans do, we’re going to science the hell out of that stuff:
The discovery of the gadusol pathway in vertebrates provides a platform for understanding its role in these animals, and the possibility of engineering yeast to efficiently produce a natural sunscreen and antioxidant presents an avenue for its large-scale production for possible use in pharmaceuticals and cosmetics.
Meaning, soon we may be taking sunscreen pills, hacked from the awesome ability of fish to protect themselves against the sun. Neat!