More than 180 species of biofluorescent fish were discovered by researchers in a new study, potentially opening up new research areas and shedding some light on the evolution of marine fishes and what role biofluorescence plays.

Biofluorescence is a process by which organisms eject light and it has been observed in butterflies, parrots, spiders, flowers, and corals.  According to Luminescent Labs, biofluorescence is not a chemical reaction, and biofluorescent organisms don’t give off light using their own power sources, but instead, “absorb light, transform it and eject- or ‘re-emit’ it as a different color.”

This is the first study showing that biofluorescence is common among marine fish species and researchers say they found biofluorescence present in both cartilaginous and bony fishes.

“We’ve long known about biofluorescence underwater in organisms like corals, jellyfish, and even in land animals like butterflies and parrots, but fish biofluorescence has been reported in only a few research publications,” said co-lead author John Sparks, a curator in the American Museum of Natural History’s Department of Ichthyology, in a statement. “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.”

The researchers found species-specific biofluorescent emission patterns among closely related species. “Based on these data, the possibility exists that marine fishes are using biofluorescence for a variety of functions, including communication (species recognition, mating), predator avoidance, and potentially even prey attraction/predation,” according to the study published in PLOS ONE.

Water absorbs most of the light emitted by the visible light spectrum, creating an underwater atmosphere that’s dark and mostly blue. Recent research shows that some fish absorb the remaining blue light and re-emit it in neon colors.

“By designing scientific lighting that mimics the ocean’s light along with cameras that can capture the animals’ fluorescent light, we can now catch a glimpse of this hidden biofluorescent universe,” said co-lead author David Gruber, an associate professor of biology at Baruch College and a research associate at the American Museum of Natural History. “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.”

How can the discovery of biofluorescent fishes open up new biomedical research areas?

“The discovery of green fluorescent protein in a hydrozoan jellyfish in the 1960s has provided a revolutionary tool for modern biologists, transforming our study of everything from the AIDS virus to the workings of the brain,” Gruber said. “This study suggests that fish biofluorescence might be another rich reservoir of new fluorescent proteins.”

The team of researchers began investigating the phenomenon of biofluorescent fish with underwater expeditions and night dives using custom-built underwater cameras with yellow filters and yellow visors to block out the blue light.

According to the statement, these expeditions, “revealed a zoo of biofluorescent fishes—from both cartilaginous (e.g. sharks and rays) and bony (e.g. eels and lizardfishes) lineages—especially among cryptically patterned, well-camouflaged species living in coral reefs. By imaging and collecting specimens in the island waters, and conducting supplementary studies at public aquariums after hours, researchers identified more than 180 species of biofluorescent fishes, including species-specific emission patterns among close relatives.”

They found that lots of the biofluorescent fish had, “yellow filters in their eyes, possibly allowing them to see the otherwise hidden fluorescent displays taking place in the water.” They believe that the yellow eye filters could be used for interspecific communication while camouflaged or during mating rituals.

Scientists also discovered that the biofluorescence was extremely variable in the fish, and could include anything from glowing mucus secretions to complex internal fluorescent patterning or eye rings, implying that biofluorescence evolved a number of times in fish.

“Our findings identify a widespread and previously unrecognized evolutionary phenomenon that provides new insights into the evolution of marine fishes and the function of light and visual systems in a marine environment, as well as providing a framework for the discovery of additional novel fluorescent proteins.”

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