The Arapaima fish lives in Amazonian lakes have evolved armor-like scales to protect itself. The fish is huge – growing up to 4 meters in length and weighing in at around 200kg and is likely to be the largest freshwater fish on the planet. Scientists are hoping that the scales can help them build more efficient armor to protect human beings.
The hardened scales are heavily mineralized and act to protect the fish from predators including the piranhas that infest the waters in which it lives. The scales remain flexible because of the existence of protrusions and ridges and there is a collagen layer underneath which binds the scales to the body without losing flexibility.
The layer appears as a series of twisting layers known as a Bouligand structure which is also seen in beetle, lobster and crab shells.
Test of Strength
A series of tests were conducted on the scales designed to see exactly how much stress they could resist.
Having soaked crushed scales in water for 48 hours the scientists exerted central pressure and pulled the edges apart. This causes the outer layer to increase in size, eventually cracking and peeling away. However, the fractures did not spread and this has been attributed to the way they are structured: The inner and outer layers of the scales work in unison to provide a light and tough barrier.
When looking to engineer armor there needs to be a combination of strength and flexibility and this is what the structure of the fish’s scales seems to achieve. If scientists can develop similarly lightweight but tough materials it could have wide-reaching impacts on industry, including aerospace engineering.