The robust scale structure of the Arapaima fish helps it cope with the razor-sharp teeth of predators in its habitat, such as piranhas.
To survive in the Amazon River basin teeming with predatory piranhas, the Arapaima gigas, a member of the dragon fish family, has evolved scales as tough as armor. The outermost layer of scales is mineralized, forming a barrier against threats like the teeth of predators. However, the raised ridges and protrusions allow the scales to remain flexible, according to research published in the journal Matter.
Arapaima can grow up to 3 meters. (Photo: Wikipedia).
The inner layer of scales is linked with collagen in a Bouligand structure. Similar to spiral staircases, this structure is also found in the shells of lobsters, beetles, and crabs, according to study co-author Wen Yang from the Nano Engineering Department at the University of California, San Diego.
To investigate the hardness of the scales, the research team from the University of California, San Diego, and the University of California, Berkeley, conducted pressure resistance tests. First, they ground the scales of the dragon fish in water for 48 hours. Then, they applied compressive force to the center of the scales while stretching the outer edges. During this process, they observed that initially, the outer layer of scales expanded, then cracked and flaked off. The scale structure helps prevent the cracks from spreading.
The research team concluded that the inner and outer scales combine to form a lightweight, flexible, yet sturdy structure. They believe this is one of the most resilient biological materials on the planet that could be modeled to create artificial armor in the future.
Arapaima gigas (giant river fish) inhabits the Amazon basin and has been introduced to Southeast Asia. Among the largest freshwater fish and the fastest-growing vertebrates on Earth, the dragon fish can grow up to 3 meters long. This species has the ability to breathe air. Every 5 to 15 minutes, they need to surface and inhale air to gather 95% of the oxygen they require. The rest is supplemented by water flowing over their gills.
