The secret behind the ghost catfish’s iridescent shimmer has been discovered by a team of scientists.
Kryptopterus vitreolus casts ethereal, shimmering rainbows down its sides as it sparkles in the water. This eye-catching shine in its otherwise glass-like body makes the Thai native a popular choice among aquarium owners around the world.
It also caught the eye of Qibin Zhao, a physicist at Shanghai Jiao Tong University in China, as he walked around an aquarium store. So, like any curious scientist, he decided to study it.
In nature, dancing rainbows known as iridescence are often caused by textures on the surface of body parts such as scales, wings or feathers. White light strikes these surfaces and is scattered upon reflection, interfering with itself in ways that accentuate different wavelengths.
The ghost catfish, however, allows 90% of light to pass through its body. It also has no scales and its skin is extremely thin (about 20 micrometers). This makes reflected scattering from its skin or scales unlikely to be responsible for a rainbow effect; something else must be at work.
Together with lead author Xiujun Fan, a materials scientist from Shanghai Jiao Tong University, Zhao and his colleagues dissected the fish to separate the skin from the back and stomach muscles.
A white laser passed through the skin without too much dispersion. The muscles were another story. Something in them caused the light waves to ripple in what is called diffractioncreating a rainbow effect.
Each muscle is made up of elastic units called sarcomeres. Using scanning electron microscopy and light microscopes, the team discovered that these fibrous units act as diffraction gratingssplitting the beam of light into a rainbow as it passed through the structure.
The changing angles of the moving fish create changing angles at which light hits the muscles, flashing colors that diffract through them through a rainbow.
Other fish have the same type of muscle, but the shine can’t be seen from the outside because their skin isn’t transparent, researchers said.
This iridescent shimmer could have evolved in the ghost catfish as a form of camouflage so it could avoid predators, researchers say. hypothesized.
Ghost catfish are not completely invisible; it still creates a shadow in the water that predators can chase away. This shadow could be concealed by casting distracting rainbow colors that mimic the diffraction patterns of sunlight on the water.
“It’s also possible that ghost catfish use the rapidly changing colors as communication signals, as we find that the fish is a very social species,” the researchers said. said.
This article was published in Proceedings of the National Academy of Sciences.