This is Scientific American's 60-second Science, I'm Christopher Intagliata.Deep in the Amazon lives one of the world's largest freshwater fish: the legendary Arapaima.It tips the scales at hundreds of pounds,making it a coveted catch for extreme anglers, like Jeremy Wade from the show River Monsters.After a dramatically scored struggle, he catches one. It takes two guys to hold it up!"There it is. Look at that for a fish! Look at that massive female Arapaima; about 150 pounds."Speaking of scales, this giant fish has another superlative quality:"It has these very impressive armored scales on its body,which prevent penetration by predators teeth yet still makes the fish quite flexible and nimble in the water."Robert Ritchie, a materials scientist at U.C. Berkeley.The predators he's talking about are piranhas.But the mighty Arapaima has them beat with its scales―one of the "toughest flexible biological materials," according to Ritchie's team.After subjecting the scales to stress tests and electron microscopy in the lab, they figured out the scales' secrets.For one, they have a hard, mineralized layer on the outside."You need the hard layer at the surface to prevent the thing from penetrating.But if the whole scale was made of this hard layer, it would just shatter, like if you tried to penetrate a piece of glass."And so the scale then has a layer of softer but tougher collagen on the inside―more resistant to cracking in a piranha's bite.