Fish Biofluorescence Has Glowed Across Oceans for 112 Million Years

Biofluorescent fish have illuminated the oceans for no less than 112 million years. As blue light strikes their skin, these creatures absorb it before releasing green, yellow, orange or red light.

Fish biofluorescence cannot be seen by people in daylight. Under suitable lighting, however, it can transform reefs into underwater neon displays. This natural spectacle developed quietly below the surface and remained largely beyond human sight until recent years.

Origins of glowing fish

Two recent studies from researchers at the American Museum of Natural History’s Richard Gilder Graduate School examine when and how this glow emerged.

The work charts biofluorescence in 459 species, revealing the remarkable range of colours that has evolved.

Scientists reviewed every recorded instance of glowing bony fish and identified a further 48 species not previously reported. Their analysis indicates that biofluorescence originated in ancient eels and has independently evolved more than 100 times since then.

“Researchers have known for a while that biofluorescence is quite widespread in marine animals, from sea turtles to corals, and especially among fishes,” said Emily Carr, lead author of both studies.

“But to really get to the root of why and how these species use this unique adaptation – whether for camouflage, predation, or reproduction – we need to understand the underlying evolutionary story as well as the scope of biofluorescence as it currently exists.”

Coral reefs accelerate fish biofluorescence

Coral reef life appears to hasten the evolution of this trait. Fish living on reefs develop biofluorescence roughly ten times more rapidly than species that remain in open water.

Following the mass extinction 66 million years ago, which saw dinosaurs disappear and reefs recover, fluorescent species increased rapidly as they moved into newly open habitats and ecological niches.

“This trend coincides with the rise of modern coral-dominated reefs and the rapid colonization of reefs by fishes, which occurred following a significant loss of coral diversity in the K-Pg extinction,” Carr said.

“These correlations suggest that the emergence of modern coral reefs could have facilitated the diversification of fluorescence in reef-associated teleost fishes.”

The expanding colour spectrum

For a second series of experiments, researchers photographed museum specimens using specialist lighting. Certain families displayed at least six separate fluorescence peaks, showing far more diversity than scientists had previously recorded.

“The remarkable variation we observed across a wide array of these fluorescent fishes could mean that these animals use incredibly diverse and elaborate signaling systems based on species-specific fluorescent emission patterns,” said study co-author John Sparks.

“As these studies show, biofluorescence is both pervasive and incredibly phenotypically variable among marine fishes. What we would really like to understand better is how fluorescence functions in these highly variable marine lineages, as well as its role in diversification.”

How glowing fish may support medicine

Fluorescent proteins taken from jellyfish revolutionised molecular biology. The numerous new shades discovered in fish may contribute to a new generation of imaging technologies, allowing doctors to identify tumours or use light to guide surgery.

For the moment, much of the ocean’s mystery remains concealed in plain view. Yet every burst of colour offers greater insight into how fish communicate, conceal themselves, hunt and locate mates, making a midnight reef resemble a quiet exchange conducted in light.

Future research into fish biofluorescence

Although these results illuminate the extensive history and variety of glowing fish, much remains to be discovered.

Researchers are now investigating how individual species perceive and use these colours in daily life. Do they glow for camouflage, to draw in mates, or to communicate signals that people have not yet learned to interpret?

The findings may explain not only how these fish flourish in underwater environments, but also assist in creating new tools for optics, communication and biotechnology.

Every finding contributes one small part to a much larger puzzle, in which light does more than illuminate the ocean: it can also guide future innovation.

The complete study was published in the journal PLOS One.