Fish has shield against piranhas


An “armored” fish living in the Amazon has evolved a remarkable multilayer defense against the voracious piranha.

Microscopic examination and mechanical testing have revealed the secrets of the Arapaima gigas, one of the biggest freshwater fish on the planet. Researchers at the University of California, Berkeley found its scales have an ultratough shell, designed to “promote tooth fracture at the point of penetration.”

The scales also have a corrugated shape, designed to deflect pressure to a thicker, more elastic layer of collagen that lies underneath. The collagen itself is arranged in twisted overlapping layers. They can slide slightly in response to a bite, causing its pressure to be spread over a wider area.

The scales “are a prime example of a biological material’s evolution for a particular function,” says the paper, appearing in the journal Nature Communications.

The arapaima is a giant carnivore, growing up to 4 meters long and weighing 200 kg. Large numbers began to be taken for food in the 19th century, and the species is now endangered.