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Science - A piranha-proof fish

Published: 10 Feb 2012

Dip a toe into the wrong lake in the Amazon, and it may get bitten off. Here, gangs of piranhas swarm almost anything that moves. Anything, that is, except the arapaima.

Dip a toe into the wrong lake in the Amazon, and it may get bitten off. Here, gangs of piranhas swarm almost anything that moves. Anything, that is, except the arapaima. This humungous fish swims unchewed, even in piranha-infested lakes and rivers. A new study reveals how: The arapaima's unique scales are tough enough to deflect a piranha's razor-sharp bite.

The study is "very nice work," says Markus Buehler, a materials scientist at the Massachusetts Institute of Technology in Cambridge. Meyers and colleagues demonstrate a common feature in nature, he says. Different materials combine to make a structure that takes on new traits.

Francois Barthelat, a mechanical engineer at McGill University in Montreal, Canada, agrees. "It's pretty impressive." Arapaimas are hardly alone in the fish world, he notes. His team previously discovered the same layered patterning in the scales of several other fish, even many "fish market" species.

No, sea bass scales can't fend off a piranha attack, but they're still surprisingly tough, given their flexibility, he says. Barthelat has taken the concept to the lab, where he and colleagues design glass that directs cracks and fractures just as fish armor does. Such designs could one day be used to make lightweight body armor, meaning that soldiers could charge into combat wearing fish scales.

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