A study appearing in the journal PLOS ONE this week shows that bioluminescence -- the production of light from a living organism -- is more widespread among marine¹ fishes than previously² understood. Most people are familiar with bioluminescence in fireflies, but the phenomenon is found throughout the ocean, including in fishes. Indeed, the authors show with genetic³ analysis that bioluminescence has evolved independently 27 times in 14 major fish clades -- groups of fish that come from a common ancestor.

 

"Bioluminescence is a way of signaling between fishes, the same way that people might dance or wear bright colors at a nightclub," said W. Leo Smith, assistant curator with the University of Kansas Biodiversity Institute, who co-authored the paper. He added that some fish also are thought to use bioluminescence as camouflage⁴.

 

Smith said the huge variety in ways bony fish can deploy⁵ bioluminescence -- such as leveraging⁶ bioluminescent bacteria, channeling light though fiber-optic-like systems or using specialized⁷ light-producing organs -- underlines the importance of bioluminescence to vertebrate fish in a major swath of the world's deep seas called the "deep scattering⁸ layer."

 

"When things evolve independently multiples times, we can infer that the feature is useful," Smith said. "You have this whole habitat where everything that's not living at the top or bottom of the ocean or along the edges -- nearly every vertebrate living in the open water -- around 80 percent of those fish species are bioluminescent. So this tells us bioluminescence is almost a requirement for fishes to be successful."

 

Indeed, the KU researcher said the most common vertebrate species on the planet lives within this habitat and is bioluminescent. 

 

"The bristlemouth is the most abundant vertebrate on Earth," Smith said. "Estimates of the size are thousands of trillions of bristlemouth fish in the world's oceans."

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