Color-Shifting Sharks

Prionace glauca is one of the rare animals that appear blue, which is why it is called the “blue shark.” 

Now scientists are able to explain why. 

“Blue is one of the rarest colors in the animal kingdom, and animals have developed a variety of unique strategies through evolution to produce it, making these processes especially fascinating,” researcher Viktoriia Kamska said in a statement. 

New research recently presented at the Society for Experimental Biology Annual Conference in Antwerp, Belgium, found that the nanostructures producing this blue hue also seem to allow the shark to change color depending on its environment. 

The team found that the secret behind the shark’s color is in the pulp cavities of its tooth-like scales – known as dermal denticles – that armor the shark’s skin. 

Inside these cavities, guanine crystals reflect blue light, while melanin-filled vesicles, called melanosomes, absorb other wavelengths. Together, they create the shark’s vivid blue appearance. 

The color results from the precise arrangement in thickness and spacing of guanine platelets, whose structure enhances reflection, while melanin absorbs stray wavelengths to deepen the color’s intensity. 

“When you combine these materials together, you also create a powerful ability to produce and change color,” said researcher Mason Dean. 

Through computer simulations, the team found that narrower spacing between guanine layers produces the shark’s signature blue hues, while wider spacing shifts the reflected color toward greens and golds, according to Cosmos Magazine. 

Researchers hypothesized that this color change mechanism could be caused by environmental factors that affect guanine crystal spacing. 

“In this way, very fine scale alterations resulting from something as simple as humidity or water pressure changes could alter body color, which then shapes how the animal camouflages or counter-shades in its natural environment,” said Dean. 

For instance, the pressure applied to a shark’s skin increases the deeper the animal swims. In this case, the guanine crystals would be pushed closer together, darkening the shark’s color to better fit in with its surroundings. 

“Not only do these denticles provide sharks with hydrodynamic and antifouling benefits, but we’ve now found that they also have a role in producing and maybe changing color too,” said Dean. 

This discovery could help improve more environmentally sustainable manufacturing in marine environments, as structural coloration is less toxic and less polluting compared to chemical coloration.