Some creatures in the animal kingdom show off spectacular colors when exposed to light, such as certain snakes, insects and peacocks. They are known as iridescent animals.
While snakes have iridescent scales and peacocks have iridescent feathers, a recent study published in PNAS indicates that in the case of the transparent ghost catfish, the iridescent shine it gives off isn’t from the fish’s scales.
The Rainbow Fish
The ghost catfish (Kryptopterus vitreolus) is a transparent fish native to slow-moving rivers and streams of Thailand, and they are also popular in freshwater aquariums. Because of its translucent scales, one can see its tiny heart beating and its spine.
(Credit: Nan Shi, Xiujun Fan, and Genbao Wu)
Transparent ghost catfish (K. vitreolus).
When light from the sun or an artificial source passes through these fish, they can give off a vibrant rainbow glow. However, unlike other iridescent animals, the study found that the ghost catfish gets its iridescent shine from its internal organs, not its scales.
According to a press release, researchers used laser light, electron microscopy and X-ray scattering to characterize the optical properties of skin and muscle samples of the fish.
Through these methods, researchers determined that the ghost catfish’s muscles have “sarcomeres with periodic band structures inside tightly stacked myofibril sheets.” This means that light passes through the muscle fibers (myosin) and causes diffraction — or the slight bending of light.
As a ghost catfish swims, the sarcomeres in the muscles expand and contract, changing lengths and creating a “quickly blinking dynamic diffraction pattern.” According to the press release, the study authors noted that though other aquatic species have similar muscle fibers in similar structures, the ghost catfish’s transparent skin allows over 90 percent of light to pass through its muscles.
Because of this finding, researchers now better understand how other aquatic species become iridescent and how other structural colors evolved in nature.