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From blue to green, red or orange: Fish put on new light

By Steve Almasy, CNN
January 9, 2014 -- Updated 1743 GMT (0143 HKT)
A green biofluorescent chain catshark (Scyliorhinus retifer) A green biofluorescent chain catshark (Scyliorhinus retifer)
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STORY HIGHLIGHTS
  • When hit with special blue light, 180 species of fish light up
  • Researchers think it may play a role in mating or in communication
  • Scientists discovered a glowing green eel when looking at reefs for biofluorescence
  • Some fish have yellow filters in their eyes, which can help them see the light show

(CNN) -- There is a light show in the ocean that you can't see, but many fish can. There's quite a display of neon greens, reds, and oranges going on underneath the surface.

Still, the discovery of what is hidden from human eyes -- biofluorescence in 180 species of fish -- brings up many questions for researchers.

Do fish use it to communicate with others? Do they use it to mate? What is its function?

Biofluorescence occurs when an organism absorbs blue light, transforms it and emits it as another color.

A team of researchers from the American Museum of Natural History and other scientific organizations published a study Wednesday in the online journal PLOS ONE, reporting the findings of the first in-depth look at biofluorescence in fish.

"We've long known about biofluorescence underwater in organisms like corals, jellyfish, and even in land animals like butterflies and parrots," said the study's co-author, John Sparks, who is a curator in the Museum's Department of Ichthyology.

He said the team stumbled on an eel that glowed green while he and a partner were studying a reef in the Cayman Islands. The discovery in a photograph of the eel lighting up underneath the blue lights they used led them to make four more trips in different parts of the world to get a closer look at the glow show.

The expeditions to the Bahamas in the Caribbean and Solomon Islands in the Pacific revealed a variety of fish living around coral reefs -- including sharks, rays, eels and lizerdfishes -- that exhibited bioflourescence. s

"Many shallow reef inhabitants and fish have the capabilities to detect fluorescent light and may be using biofluorescence in similar fashions to how animals use bioluminescence, such as to find mates and to camouflage," Sparks suggested, while adding the reasons will need further study.

So how do the fish recognize it? Many of them have yellow filters in their eyes, "possibly allowing them to see the otherwise hidden fluorescent displays taking place in the water," a news release from the museum of natural history said.

"The cryptically patterned gobies, flatfishes, eels, and scorpionfishes -- these are animals that you'd never normally see during a dive," Sparks said. "To our eyes, they blend right into their environment. But to a fish that has a yellow intraocular filter, they must stick out like a sore thumb."

Some scientists cautioned that the bioflouresence might look neat in photos using special lights but also have no function.

Nico Michiels, a zoologist at the University of Tübingen in Germany, and Steven Haddock of the Monterey Bay Aquarium Research Institute in California, indicated to Science Now that the need for special technology to view what the website called weak fluorescence "casts doubt on the usefulness of the coloration in the fish's dimly lit natural environments."

Sparks said it will be interesting to see what the team finds next.

"This paper is the first to look at the wide distribution of biofluorescence across fishes, and it opens up a number of new research areas," he said.

He added that there may be fluorescent proteins involved, ones that could be used in biomedical research.

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