New study finds blue sharks can change colour in response to environment

The iconic bright blue colour of the blue shark might not be as fixed as once thought. New research presented at the Society for Experimental Biology Annual Conference suggests these sharks could alter their colouring — shifting from vibrant blue to hues of green and even gold.

The study reveals that the secret behind the shark’s striking appearance lies in its scales. Blue sharks (Prionace glauca) are covered in dermal denticles — tooth-like scales — that contain special internal structures. According to the research, it’s these tiny components that both produce the shark’s vivid colour and may allow it to change.

“Blue is one of the rarest colours in the animal kingdom,” says Dr Viktoriia Kamska of City University of Hong Kong. “Animals have developed a variety of unique strategies through evolution to produce it, making these processes especially fascinating.”

Inside the shark’s dermal denticles are pulp-like cavities filled with guanine crystals, which reflect blue light, and sacs containing melanin — the pigment that absorbs other wavelengths of light.

“These components are packed into separate cells, reminiscent of bags filled with mirrors and bags with black absorbers, but kept in close association so they work together,” explains Kamska.

The research team, including Professor Mason Dean, used a combination of physical observation and digital modelling to understand the shark’s colouration. “When you combine these materials together, you also create a powerful ability to produce and change colour,” he says. “What’s fascinating is that we can observe tiny changes in the cells containing the crystals and see and model how they influence the colour of the whole organism.”

The findings indicate that the spacing of these nanocrystals determines the colour seen by observers. When the crystals are tightly packed, the shark appears deep blue. As the crystals separate, the reflected colour shifts — with green and gold tones emerging. These subtle changes may occur in response to environmental factors like water pressure or humidity.

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

In deeper waters, where pressure is higher, the crystals may be compressed, deepening the blue — helping the shark blend in with its surroundings.

The team is keen to observe whether this colour-shifting phenomenon occurs in the wild. If confirmed, it would mark a significant discovery about how sharks adapt their appearance in varying ocean conditions. It may even have implications for biomimicry and sustainable material science.

“A major benefit of structural colouration over chemical colouration is that it reduces the toxicity of materials and reduces environmental pollution,” Kamska points out.

Sharks would not be alone in the underwater world when it comes to adaptive colouration. Cephalopods like squid, octopus, and cuttlefish famously change colours rapidly for camouflage or communication, while seahorses use expandable pigment sacs called chromatophores to blend into their surroundings.

Understanding the unique evolutionary mechanisms behind colouration in sharks — which split from bony fish hundreds of millions of years ago — could offer new insights into both marine biology and material science.

“We know a lot about how other fishes make colours, but sharks and rays diverged from bony fishes hundreds of millions of years ago,” says Professor Dean, “so this represents a completely different evolutionary path for making colour.”

By Aghakazim Guliyev