• 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)

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