Glowing swell shark
glowing swell shark

Image of the Day: Fluorescent Sharks

A newfound family of metabolites emits green light in response to the blue light of the deep ocean, causing certain sharks to glow.

Nicoletta Lanese
Aug 13, 2019

ABOVE: The swell shark (Cephaloscyllium ventriosum) glows a bright green under blue-filtered light.

Small-molecule metabolites in sharks’ skin help the creatures stand out against the dark ocean floor by glowing bright green, researchers reported August 8 in iScience

Swell sharks (Cephaloscyllium ventriosum) and chain catsharks (Scyliorhinus retifer) can only see light in the blue-green spectrum, the dominant colors found in their deep-sea habitat. Both sharks sport light and dark patterns on their skin, and in the eyes of a fellow shark, the pale patches gleam a fluorescent green. Scientists found that this lighter skin contains a previously unknown family of small-molecule metabolites, derived from the amino acid tryptophan, which emit green light in response to blue.  

“The exciting part of this study is the description of an entirely new form of marine biofluorescence from sharks,” says coauthor David Gruber, a biologist at the City University of New York, in an announcement. The fluorescent compounds may also provide protection against microbial infections.

Coauthor David Gruber spots a shark with a “shark-eye” camera, an instrument that uses filters to simulate what sharks see underwater.

H.B. Park et al., “Bright-green biofluorescence in sharks derives from bromo-kynurenine metabolism,” doi:10.1016/j.isci.2019.07.019, iScience, 2019.

Nicoletta Lanese is an intern at The Scientist. Email her at