Biologists have figured out how fish get rainbow colors without the use of pigments
(ORDO NEWS) — Glass catfish are almost transparent, you can only see their head and back, which shimmers with all the colors of the rainbow.
This coloration turned out to be associated with a very unusual mechanism: the skin of these fish transmits light, and the muscle fibers separate it into individual colors, like tiny prisms.
Popular aquarium fish, the glass catfish Kryptopterus vitreolus , do not produce pigments and are almost completely transparent.
In the water, only their heads and backs are clearly visible, which, under certain conditions, begins to shimmer with all the colors of the rainbow. Some other animals also demonstrate this iridescent coloration.
Rainbow colors can be found in bird feathers , mollusc shells, butterfly wings, reptile scales. They are usually associated with special microscopic structures on the surface.
In contrast to the pigment coloration, which occurs due to the absorption of photons of certain wavelengths and the reflection of others, the structural one is caused by their interference after reflection from different parts of the microstructures.
However, the scales of K. vitreolus catfish are transparent and freely transmit light, so their iridescence has remained a mystery until now.
Qibin Zhao and his colleagues at Shanghai Jiaotong University examined various glass catfish tissues under a microscope to see exactly where photon-manipulating structures lurk within them.
They were not in the scales or in the skin, but such elements were found in the muscles of the fish.
Their sarcomeres – the sites where the protein filaments connect that provide muscle contractions – are transparent and work like microscopic prisms, decomposing the incident radiation into separate colors.
Until now, such a mechanism for the appearance of color has not been known in wildlife, although it is possible that sarcomeres of some other fish are able to work in a similar way.
But only in glass catfish, with their tiny body and transparent skin, this effect can manifest itself clearly, allowing the backs to shimmer with iridescent colors.
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