This tiny aquarium fish from Thailand is transparent: It has skin that is nearly translucent. Nevertheless, its body flickers with shimmering rainbow colours when the light hits it just right. Scientists have now discovered how this fish, often known as the ghost catfish, produces its iridescent shine. According to a study released in the journal Proceedings of the National Academy of Sciences, that light originates from the inside. Light strikes small structures in the fish's muscle as it goes through the skin, creating a multicoloured spectrum as a result. At an average length of only a few inches (centimetres), the ghost catfish, often referred to as the glass catfish, is a small species that is native to rivers in Thailand. It is marketed as an aquarium fish around the world. Other creatures are also iridescent, creating the shimmering rainbow effect where colors shift as you move. Usually, they have shiny outer surfaces that reflect the light – like a hummingbird’s feathers or a butterfly’s wings, explained Arizona State University biologist Ron Rutowski, who was not involved with the research.