NEW YORK — You can see right through this little aquarium fish from Thailand: Its skin is almost completely transparent. But when the light hits it just right, its body flickers with shimmering rainbow colors.
Now, scientists have figured out how this fish — called the ghost catfish — creates its iridescent glow.
This image provided by Qibin Zhao shows ghost catfish showing iridescence. The ghost catfish has a see-through body that flickers with rainbow colors when the light hits it.
That glow comes from within, according to a new study published in the journal Proceedings of the National Academy of Sciences. As light passes through the fish’s skin, it hits tiny structures in the muscle that turn the light into a colorful spectrum.
The ghost catfish — sometimes known as the glass catfish — is a small species native to rivers in Thailand, averaging just a few inches long. It's sold around the world as an aquarium fish.
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.
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The ghost catfish has a see-through body that flickers with rainbow colors when the light hits it.
But the ghost catfish has no scales, said senior author Qibin Zhao, a physicist at China’s Shanghai Jiao Tong University, who became fascinated by the fish after seeing it in an aquarium store.
Instead, it has tightly packed structures in the muscles that can bend light into rainbow hues, which researchers found after shining different lights and lasers onto its body in the lab. As the ghost catfish swims, those muscles relax and tighten, sending off a glinting range of colors.
And the very see-through skin, which lets in around 90% of outside light, is essential: “We wouldn’t be able to see the colors if the skin of the fish is not so transparent,” Zhao said in an email.
Some species use their iridescence to attract mates or give off warning signals, but it’s not clear whether the ghost catfish's colors serve a purpose, Rutowski said.
Photos: Murky waters for global aquarium trade
A starfish crawls along coral reefs, damaged from years of dynamite fishing, in Les, Bali, Indonesia, on April 11, 2021. Cyanide fishing was also common in the area. There have been efforts to reduce some of the most destructive practices, but the trade is extraordinarily difficult to regulate and track as it stretches from small scale fisherman in tropical seaside villages through local middlemen, export warehouses, international trade hubs and finally to pet stores in the U.S., China, Europe and elsewhere. (AP Photo/Alex Lindbloom)
Made Partiana uses a net to catch aquarium fish on north coast of Bali, Indonesia, on April 10, 2021. Millions of saltwater fish are caught in Indonesia and other countries every year to fill ever more elaborate aquariums in living rooms, waiting rooms and restaurants around the world with vivid, otherworldly life. (AP Photo/Alex Lindbloom)
Made Partiana looks at sea urchins in a tank in the LINI center in Les, Bali, Indonesia, on April 12, 2021. “I hope that [healthier] coral reefs will make it possible for the next generation of children and grandchildren under me,” Partiana says. He wants them to be able to “see what coral looks like and that there can be ornamental fish in the sea.” (AP Photo/Alex Lindbloom)
Workers sort fish at a middle man house in Les, Bali, Indonesia, on April 11, 2021. (AP Photo/Alex Lindbloom)
Villagers hang out near boats along the coast in Les, Bali, Indonesia, on April 9, 2021. The area is commonly used for aquarium fishing. (AP Photo/Alex Lindbloom)
Dead fish lie in a container at a sorting station in Les, Bali, Indonesia, on April 9, 2021. (AP Photo/Alex Lindbloom)
A worker checks a sort and order list at middle man area in Les, Bali, Indonesia, on April 10, 2021. (AP Photo/Alex Lindbloom)
Workers sort fish in Les, Bali, Indonesia, on April 11, 2021, for shipment to Denpasar for export. Nearly 3 million homes in the U.S. keep saltwater fish as pets, according to a 2021-2022 American Pet Products Association survey. (AP Photo/Alex Lindbloom)
Pak Ketut, who has been selling fish for over a decade sits in aquarium middle man house in Les, Bali, Indonesia, on April 9, 2021. (AP Photo/Alex Lindbloom)
Workers sort aquarium fish caught and delivered to an export warehouse in Denpasar, Bali, Indonesia, on April 12, 2021. Fish from around Indonesia are brought to this facility. (AP Photo/Alex Lindbloom)
Made Partiana inspects a tank at the LINI center in Les, Bali, Indonesia, on April 12, 2021. The Bali-based nonprofit works for the conservation and management of coastal marine resources. (AP Photo/Alex Lindbloom)
Local villager and fisherman Made Partiana and a local villager search for fish off the coast of Les, Bali, Indonesia, on April 10, 2021. (AP Photo/Alex Lindbloom)
Made Partiana and another villager sort fish caught during the day on April 11, 2021. “I hope that [healthier] coral reefs will make it possible for the next generation of children and grandchildren under me,” Partiana says. He wants them to be able to “see what coral looks like and that there can be ornamental fish in the sea.” (AP Photo/Alex Lindbloom)
Made Partiana walks along beach area at Les, Bali, Indonesia, on April 11, 2021, as he prepares to catch aquarium fish. Over the years Partiana began to notice the reef was changing. “I saw the reef dying, turning black,” he says. “You could see there were less fish.” (AP Photo/Alex Lindbloom)
Boats line the coast of Les, Bali, Indonesia, on April 11, 2021. This site is commonly used for aquarium fishing. In the vast archipelago of Indonesia, there are about 34,000 miles (54,720 kilometers) of coastline across some 17,500 islands. That makes monitoring the first step of the tropical fish supply chain a task so gargantuan it is all but ignored. (AP Photo/Alex Lindbloom)
The center of Les, Bali, Indonesia is seen on April 11, 2021. The saltwater aquarium fishing town is tucked between the mountains and ocean in northern Bali. (AP Photo/Alex Lindbloom)
