The next breakthrough in medical implants could come from a terrifying, needle-fanged fish lurking deep in the ocean. 

Experts have long known that the deep ocean is a living light show. Roughly 75 percent of marine organisms are bioluminescent, using specialized light-emitting organs called photophores to hunt, mate, and survive in the pitch black. 

But a new study by Hiroshima University in Japan has examined unique structures present in one specific predator: the slender fangjaw (Sigmops gracilis). Interestingly, this bioluminescent fish has a complex built-in light system.

Uses living prisms

For two decades, Professor Masakazu Iwasaka of Hiroshima University has chased the secrets of fish scales. Specifically, he studies guanine crystals, the biological structures that give fish their iridescent sheen. In common shallow-water species like goldfish, these crystals act like millions of microscopic mirrors, reflecting light straight back.

The slender fangjaw plays by entirely different rules.

When Iwasaka examined the deep-sea predator on a research vessel, he discovered that its light organs are surrounded by dense clusters of needle-shaped guanine platelets. These structures don’t just bounce light around. Thanks to their unique, needle-thin shape and layered setup, they act less like mirrors and more like prisms.

The structures bend, scatter, and actively manipulate the direction of light.

“In this study, I confirmed strong anisotropic reflection — meaning the reflected light changes significantly depending on the direction the light comes from. This suggests a previously unrecognized role guanine crystals play in controlling light direction,” Iwasaka said in the press release.

Future medical devices

To map this phenomenon, the team manipulated the guanine crystals using electromagnets to shift their positions while exposing them to an external light source. Furthermore, light scattering was filmed and analyzed at various angles to record how these microscopic structures steer the fish’s glow.

Surprisingly, the fish’s body acts like a living photonic crystal, trapping leaked light and recycling it to maximize brightness where it matters most.

According to the study authors, the layered crystalline guanine platelets could provide insights into biomimetic designs that maximize and recycle leaked light, rather than merely reflect emitted light.

Engineering light inside the human body is highly difficult. Fluids block it. Tissue absorbs it. Yet, light is essential for everything from tracking internal biometrics to activating targeted cancer therapies. 

As the slender fangjaw’s prism-like crystals are perfectly optimized to manipulate light in water, this structure offers a blueprint for highly efficient microscale medical implants.

The takeaway is clear: the deep ocean is a living laboratory of untapped tech. To unlock it, researchers have to leave dry land behind.

“While examining deep-sea fish on board a research vessel, I realized important insights could not be obtained using only laboratory-based materials,” Iwasaka said. “This experience led me to explore a new direction—biomimetics inspired by unknown phenomena observed in the field.”

We know less about the ocean floor than we do about deep space, and its strange inhabitants can seem alien. Yet, the slender fangjaw proves that the creatures that look like monsters might actually hold the blueprints for our future.

The findings were published in the journal Biointerphases on May 26.