The scales of the arapaima combine flexibility with toughness due to a collagen interior and a highly mineralized external layer.

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“The scales of the Arapaimas, a large freshwater fish (up to 200 kg), are a superb example of a natural material that has evolved to provide protection against predators. The Arapaimas lives primarily in Amazon basin lakes that become infested with piranhas as the dry season advances and is covered with scales having up to 10 cm length. They have a collagen interior with a highly mineralized external layer. The collagen fibers form a cross-lamellar arrangement which produces a laminate composite. The internal collagenous layer provides the flexibility to the scales, which can undergo significant elastic deformation prior to failure, providing considerable toughness. The mineralized exterior provides the required protection against predation. The flexibility of the biomineral is enabled by two factors: (i) a corrugated configuration in which the tensile strains are minimized; (ii) a graded composition.” (Meyers et al. 2012: B1)

Journal article
Battle in the Amazon: Arapaima versus PiranhaMeyer MA; Lin YS; Olevsky EA; Chen P-Y

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Journal article
Characterization of the nanocomposite laminate structure occurring in fish scales from Arapaima gigas

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