In the depths of the ocean, the blue shark (Prionace glauca) masters a subtle art of disguise, shifting its hue from deep blue to silver or even gold to evade predators and prey. Unlike the flashy transformations of chameleons or octopuses, this shark's color-changing ability hinges on nanoscale structures in its tooth-like scales, called dermal denticles. A team from the University of Hong Kong, led by Professor Mason Dean and post-doctoral researcher Viktoriia Kamska, has decoded this phenomenon using a blend of electron microscopy, 3D segmentation, and digital simulations. Their findings, presented at the Society for Experimental Biology Annual Conference 2025, reveal how nature’s engineering could revolutionize human technology.

The Science Behind the Shift

Blue sharks owe their striking coloration—blue on top, silver on the sides, and white underneath—to two key components in their dermal denticles: guanine crystals and melanosomes. Guanine crystals act as microscopic mirrors, reflecting specific light wavelengths, while melanosomes absorb light like black paint. As Kamska explains:

"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."

Through painstaking dissection and high-resolution imaging, the team discovered that each scale contains up to 152 guanine crystals, each just nanometers in size. Digital models showed that minute changes in crystal angles or the spacing between them can alter reflected light, shifting the shark's color from blue to gray, green, or gold. For instance:
- Tighter crystal spacing: Reflects blue light.
- Wider spacing: Shifts to green or gold hues.
- Crystal angle adjustments: Transforms blue to silver.

This sensitivity suggests environmental factors like water pressure or humidity could tweak the shark's camouflage in real-time, a passive adaptation perfected over millions of years of evolution.

From Ocean Depths to Lab Bench

The research transcends marine biology, offering tangible insights for bioengineering. Sharks diverged from bony fishes over 400 million years ago, meaning their color mechanism represents a unique evolutionary pathway distinct from most studied species. Dean highlights the potential: "As nanofabrication tools get better, this creates a playground to study how structures lead to new functions." Possible applications include:
- Adaptive nanofabrics: Materials that change color based on environmental stimuli, useful for military camouflage or responsive building coatings.
- Biomedical sensors: Guanine crystal arrays could inspire diagnostic tools that shift color in response to biochemical changes.
- Energy-efficient displays: Mimicking these structures might lead to low-power optical devices without synthetic dyes.

Future work will observe sharks in their natural habitat to validate lab findings, but the groundwork is laid for cross-disciplinary innovation. In a world racing toward sustainable tech, the blue shark’s ancient secrets remind us that some of the most advanced engineering is already swimming in our oceans—waiting to be harnessed.

Source: Discover Magazine