What color is a lumpfish? The answer is more complicated than you think.
These bumpy bottom fish, found in the North Atlantic and parts of the Arctic Ocean, come in a variety of colors, which change as the fish ages. However, scientists believe they have identified the fish’s true color, fluorescent green.
In a study published this month in the Journal of Fish Biology, scientists found that lumpfish glow under UV light. They believe that these fish use their biofluorescent radiation to identify and possibly communicate with each other.
In recent years, biofluorescence has been observed in cat sharks, wombats, flying squirrels and many other species. And now add the lumpfish to the natural cast of secretly bright animals.
Lumpfish are solitary creatures that spend most of their lives on the seabed. These fun fish cling to rocks and seaweed, using a modified pelvic fin on their underside that acts like a suction cup to help them hang around until something tasty swims up.
They have also become pseudo-celebrities on TikTok, where a relentless stream of videos posted by researchers and anglers has amassed millions of views.
“It’s a pretty clumsy, clumsy fish,” said Nathaniel Spada, a research assistant at the Woods Hole Oceanographic Institution in Massachusetts and a part-time lumpfish influencer. He didn’t participate in the study, but his Werner Herzog-inspired TikToks about lumpfish in his lab have been viewed millions of times. “I didn’t expect it to be as popular as it is,” he said, “but I should have thought because it really is a cool fish.”
Last year, Dr Thomas Juhasz-Dora, a veterinarian and PhD student at University College Cork in Ireland, became curious when he looked into the bulging eyes of a lumpfish in his lab – and thought of an idea . He had observed biofluorescence in other marine species and wanted to know if his lumpfish possessed this trait. He collected 11 juvenile lumpfish and photographed them under different lighting conditions. Under regular light, they appeared sea-foam green. But when exposed to UV light, their whole body emitted a brilliant neon-green glow.
“I was like ‘wow,'” said Dr. Juhasz-Dora, who was amazed by the intensity of the fish’s biofluorescence. This phenomenon occurs when an organism absorbs ultraviolet rays, usually invisible to humans, and re-emits them as colors we can see, usually red, orange or green. This should not be confused with bioluminescence, in which animals produce their own light via a chemical reaction.
Many species have special filters in their corneas that allow them to see biofluorescence without the aid of UV light. Dr. Juhasz-Dora suspects that lumpfish are equipped with these filters, which would allow them to somehow signal to their own species while remaining safe from predators.
“It’s certainly plausible,” said Elizabeth Fairchild, a researcher and associate professor at the University of New Hampshire who studies lumpfish and other commercially farmed aquatic species.
The fish can also use its biofluorescence to attract prey, but Dr. Fairchild’s money is on the communication. “Communication is probably the likely answer,” she said, “it’s just that we don’t know what they’re communicating.”
It is also possible that biofluorescence is useless. However, Dr Fairchild, who was not involved in the study, said this was unlikely given the prominence of lumpfish staining.
“Lompfish has such crazy color plasticity,” Dr. Fairchild said. As hatchlings, they can be almost any color of the rainbow. As juveniles, their thick, knobbly skin changes color to match their surroundings, helping to hide them from predators. When they reach adulthood, lumpfish develop pale gray to light blue skin. However, this changes during the breeding season, when the males turn red-orange and the females blue-green.
How and why biofluorescence evolved in lumpfish is one of the many questions raised by Dr. Juhasz-Dora’s discovery. He and his colleagues are currently studying whether the lumpfish can control its biofluorescence. Their recent discovery “has opened the door to new discoveries,” he said. “It allows us to really see the world from their perspective, rather than our own.”