[Skunk City]

"Though they can’t say for sure what purpose sandercyanin serves, researchers theorize it may aid in shielding the fish from the sun’s ultraviolet (UV) radiation. “Sandercyanin contains biliverdin, which is a byproduct of the hemoglobin carried by red blood cells,” says Schaefer. “One factor that causes hemoglobin to break down into biliverdin is exposure to UV radiation.”*Because biliverdin is known to act as a sunscreen of sorts in some species of animals, it is possible that, in an ironic twist of science, blue walleyes could be protecting themselves from the sun by excreting excess amounts of the very substance caused by its radiation. “That’s the hypothesis of the biochemists and geneticists who have worked on this project,” says Schaefer. He notes that production of sandercyanin is greatest in the summer months, corresponding to peak periods of sunlight, and the blue coloration is found only on the fish’s dorsal regions—which receive the highest UV doses.*An increase in the number of blue walleyes may be due to decreases in the ozone layer that protects Earth from UV radiation. “They may have always had the ability to produce sandercyanin and are just needing it now,” says Schaefer. He notes that some normally colored yellow walleyes also produce blue mucus, but it is most noticeable on the albino walleyes lacking yellow skin pigment. The albinism is likely the result of a recessive gene."