Nature’s arms race

  • Arapaima. Picture by Ronald Decloux
  • Red-bellied piranha. Picture by Getty Images.
  • Corrugated scales allow the fish to flex as it moves. Image credit: Jacobs School of Engineering
  • Arapaima scales have internal layers of collagen fibres stacked in alternating directions to one another for maximum toughness. Illustrated by Dogo
Date:21 July 2012 Tags:, ,

The Brazilian Arapaima makes a large, tempting meal for the schools of piranha that share its river habitat. Good thing, then, that this prey’s scales are impervious to piranha teeth; the scales have a hard, mineralised layer that covers tough muscle. Engineers at UC San Diego attached piranha teeth to a hole punch machine to simulate attacks. The teeth penetrated the scales part-way, then broke. The researchers suggest that similar designs could produce stronger body armour, better insulation and advances in aerospace technology. – Alex Hutchinson

Fish face-off

ARAPAIMA
Scientific name: Arapaima gigas
Length: 2 to 2,4 m
Habitat: Amazon River basin
Outer scales: Up to 10 cm long
Hardness of outer layer: 500 megapascals
Hardness of inner layer: 200 megapascals
vs
RED-BELLIED PIRANHA
Scientific name: Pygocentrus nattereri
Length: 76 mm to 230 mm
Habitat: South American rivers
Bite force: 32 kg (30 times its body weight)