Triangular structures are responsible for the iridescence of fish
Triangular structures are responsible for the iridescence of fish lead image
The ability to control and manipulate light is an important characteristic for many living creatures, aiding with camouflage and communication. These properties have often been mimicked for technological applications but doing so requires an intricate understanding of the light control mechanism. Potentially opening the door to new photonic applications, Masakazu Iwasaka observed triangular structures in fish scales that are responsible for their characteristic iridescence.
According to Iwasaka’s findings, guanine platelets in fish scales, which are components of nucleic acids present in DNA, are connected to one another by fibers at 60 degree angles, creating periodic structures of equilateral triangles. Water enters the open space between the fibers, modulating the reflectiveness of the platelets when multiple layers with different refractive indices overlap.
By removing the platelets from the scales of two species of fish, goldfish and Japanese anchovy, Iwasaka studied the shiny coatings using field-emission scanning electron microscopy and transmission electron microscopy.
He was unable to determine the intrinsic makeup of the fibers themselves, which will be a topic for further study. If any component contains a material other than guanine, additional investigations will be needed to fully characterize the light control properties of the triangular structures.
“We can expect that the newly found triangular structures may concern optical metamaterials or photonic band gaps,” Iwasaka said. “More advanced studies on guanine platelet utilization in many other species of fishes may allow us a chance to discover a fish guanine platelet as an optical metamaterial.”
Source: “Hidden triangular grating structures in biogenic guanine platelet,” by Masakazu Iwasaka, AIP Advances (2020). The article can be accessed at https://doi.org/10.1063/5.0023853 .
