Scientists have discovered more than 180 species of fish that glow in a wide range of colours and patterns, ranging from simple eye rings to complex fluorescent patterns throughout the body.
The research, led by scientists from the American Museum of Natural History shows that biofluorescence — a phenomenon by which organisms absorb light, transform it, and eject it as a different colour — is common and also variable among marine fish species, indicating its potential use in communication and mating (scroll down for video).
"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 Museum’s Department of Ichthyology. "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."
Unlike the full-colour environment that humans and other terrestrial animals inhabit, fishes live in a world that is predominantly blue because, with depth, water quickly absorbs the majority of the visible light spectrum. In recent years, the research team has discovered that many fishes absorb the remaining blue light and re-emit it in neon greens, reds, and oranges, as the photo below shows.
"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."
The team's research has 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, identifying more than 180 species of biofluorescent fishes, including species-specific emission patterns among close relatives.
The team also noted that many biofluorescent fishes have yellow filters in their eyes, possibly allowing them to see the otherwise hidden fluorescent displays taking place in the water. Although more research is needed, this finding indicates that biofluorescence could be used for interspecific communication while remaining camouflaged to predators. This ability might be especially important during full moons, when fishes have been shown to partake in mating rituals.
"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."
In addition, the research revealed that fish biofluorescence is extremely variable, ranging from simple eye rings to glowing green mucus secreted on the outside of fishes to complex fluorescent patterns throughout the body, including internally, suggesting that the ability to glow evolved a number of times in fishes.
Check out the video below, which includes some fabulous underwater footage.
The results of the study are published in PLOS ONE.
Why not take out a subscription to Practical Fishkeeping magazine? See our latest subscription offer.
Don't forget that PFK is now available to download on the iPad/iPhone.