Uncovering the Secrets of the Toughest Fish Scales on Earth

The arapaima or pirarucu, native to the Amazon. (Jeff Kubina via Wikipedia [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)])
(CN) – The design of the armor-like scales of an Amazonian fish could have military applications, researchers said in a study Wednesday.

The exceedingly rare and massive Arapaima gigas fish, which is also known as the South American pirarucu, can grow to lengths of 15 feet and develop multilayered scales – some as thick as a grain of rice. The species developed its scales over time in order to protect itself from grisly piranhas lurking in its habitat.

Found primarily in the Amazon basin, the male fish are known to swim around females for their protection and carry their young in their mouths until they can survive independently.

Engineers from the University of California, Berkeley, and UC San Diego, who specialize in developing synthetic armors, began studying the arapaima after struggling to create a tough, yet flexible material.

After researchers submerged arapaima scales in water for 48 hours, they began to tear the scales apart while also adding pressure to a central point.

As pressure built up, researchers observed the hardened layer of the scale cracking and peeling off.

Understanding the structural design of the scales proved to be critical as scientists learned that the pressure could only deform the scale, and not break it, researchers said in the study, published in the journal Matter.

Closeup of the arapaima gigas’ scales. (T. Voekler via Wikipedia)

The scales’ hardened layers are fused together at “an atomistic level” by collagen, similar to the way layers of plastic webbing give bulletproof vests their toughness, researchers said in a statement.

Lead author and UC Berkeley researcher Robert Ritchie said that mineralized collagen gives the arapaima scales a hardness that scientists have not yet been able to replicate.

“A window may appear strong and solid, but it has no give. If something attempted to puncture it, the glass would shatter,” Ritchie said. “When nature binds a hard material to a soft material, it grades it, preventing this shattering effect.”

Ritchie said that “potentially impermeable” armor could be developed by mimicking the biotechnology of arapaima scales.

Other fish use collagen to thicken their scales but no other species does so at the level that the arapaima does.

The study was primarily funded by the U.S. Air Force Office of Scientific Research.

 

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