'Day-Glo' Fish Shine Red Light

Sept. 16, 2008 -- It was staring them in the face, but somehow generations of marine biologists have failed to notice that a lot of fish in the sea glow a fluorescent red, according to a study published Monday.

This unheralded talent for neon-like crimson displays is more than a curiosity, and is sure to create waves -- and a bit of embarrassment -- among ichthyologists, as fish experts are called.

It has long been axiomatic that red light is simply not part of the mental universe of marine fish because the sunlight's longest visible wavelengths do not penetrate below a depth of 30 feet.

A fire-engine red diving suit at 65 feet, for example, will appear dark grey or black to anyone -- or any fish -- that happen to be in the vicinity.

Dive far enough beneath the surface, and there is simply no red to be seen.

This foreshortening of the color spectrum under the waves was also assumed to correspond to a narrowed field of vision in fish, said the study's lead researcher in an interview.

"The general consensus, which dominated fish literature for 20 or 30 years, was that fish don't see red very well or at all," explained Nico Michiels, a researcher at the University of Tubingen in Germany.

From an evolutionary standpoint, in other words, why develop a skill that you will never be able to use?

But conventional wisdom, it seems, was flat-out wrong.

"We have been blinded, literally, by the blue-green light that is available on reefs in the daytime," said Michiels.