While diving in Greenland’s frigid waters in 2019, researchers from the American Museum of Natural History came across a snailfish with the remarkable ability to glow green and red. This deep-sea dwelling fish lives in the crevices of icebergs, and its glowing ability, or biofluorescence, is rare among Arctic fish, per a museum statement. Intrigued by its glow, the scientists decided to collect a juvenile snailfish—barely the size of a fingernail—and look closer at the animal’s genes.
But when they sequenced the snailfish DNA, it revealed something else surprising: an unusually high amount of genes coded for making antifreeze proteins that prevent these fish from freezing.
“Similar to how antifreeze in your car keeps the water in your radiator from freezing in cold temperatures, some animals have evolved amazing machinery that prevent them from freezing,” explains David Gruber, a biologist at the City University of New York’s Baruch College, in a statement.
The snailfish’s antifreeze prevents ice crystals from forming inside its body, allowing it to live in water temperatures that are below the freezing point for fish blood, per Gothamist's Rosemary Misdary. “We already knew that this tiny snailfish, which lives in extremely cold waters, produced antifreeze proteins, but we didn’t realize just how chock-full of those proteins it is,” Gruber says in the statement.
In a study published last week in the journal Evolutionary Bioinformatics, Gruber and others examined the transcriptome—or the active protein-coding portion of an organism's genome—of a juvenile variegated snailfish (Liparis gibbus). They found it contained the highest expression of antifreeze proteins ever recorded, per the statement.
“In retrospect it makes sense—of course a juvenile fish living on an iceberg is making lots of proteins that prevent it from freezing,” Gruber tells Popular Science’s Jocelyn Solis-Moreira. The finding shows that juvenile snailfish invest a lot of energy in creating these proteins, researchers say.
But Chi-Hing Christina Cheng, an evolutionary biologist at the University of Illinois Urbana-Champaign who was not involved with the study, tells Popular Science that with the information the researchers have now, it’s possible the antifreeze proteins might be expressed for another developmental reason, rather than warding off the cold. Instead of just looking at the snailfish transcriptome, which only contains instructions for creating proteins, she tells the publication that the researchers should examine how much antifreeze protein is actually in the animal’s blood plasma.
“If all these detected transcripts are actually made into functional antifreeze proteins, the plasma antifreeze activity would be high,” she tells Popular Science. “But if the plasma antifreeze activity is low, then it’s questionable that these transcripts are made into active antifreeze proteins.”
As climate change warms the Arctic, this cold-adapted species will face new risks, researchers say. In a changed environment, “more temperate species that were previously unable to survive in sub-zero seawater temperatures” could move in and compete with snailfish for food, per the study.
If the current rate of melting continues, the Arctic could lose all its ice by 2040, according to a 2019 analysis. Standing among the melting ice feels like being “in a freezer that had been left open overnight,” Gruber tells New Scientist’s Corryn Wetzel. “It made us think, wow, I wonder what’s going to happen to this fish when there are no icebergs? Its superpower is no longer a superpower.”