The arapaima has evolved scales tough enough to defend against razor-sharp teeth, a great feature for military body armor. Via Popular mechanics
The U.S. Air Force studied how an Amazonian fish can survive in the same waters as schools of deadly piranha. The arapaima, a slow-moving, torpedo-shaped fish should be easy prey for a pack of the carnivorous fish but it isn’t—thanks to the set of scales it’s evolved over millions of years. The Air Force hopes studying the scales could lead to better protection for humans and airplanes.
The arapaima fish is a flat-headed, air-breathing fish native to Brazil, Peru, and Guyana. The arapaima is possibly the world’s largest freshwater fish, reaching lengths of up to 10 feet and up to 440 pounds. The fish are air breathers, gulping air to survive and allowing it to live in oxygen-low waters.
But the arapaima’s real trick was evolving scales that can resist the sharp teeth of predators, especially piranha. According to Reuters, the scales are said to be impervious while still being flexible. Researchers credit millions of years of evolution in close proximity to deadly fish like the piranha.
Laboratory tests revealed the scales “have a hard mineralized outer layer to resist penetration that is bound to a tough-but-flexible inner layer by collagen—the main structural protein in skin and other connective tissues in the body.” Powerful bite-like motions deformed but did not destroy the collagen.