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The variegated snailfish produces soaring levels of antifreeze proteins, which help the species avoid freezing to death in Greenland’s icy waters.

and at the American Museum of Natural History in New York made the unexpected discovery on an expedition off the coast of eastern Greenland in 2019.

“It feels like you’re on another planet,” says Gruber, describing scuba diving in the frigid landscape. When they finally spotted the 18-millimetre long bioluminescent fish, it was tucked in a crevice of an iceberg. “Because it was one of the few fish living on the iceberg, it had to be doing something special to be able to make [the iceberg] its home.”

At first, Gruber and Sparks were intrigued by the snailfish’s (Liparis gibbus) known ability to bioluminesce shades of red and green. But when they examined the fish’s DNA, they found the species was hiding another remarkable trick: genes coded for churning out antifreeze proteins.

These special proteins bind to water to limit the size of ice crystal formation, keeping the animal’s blood more like a slushie, instead of frozen solid.

Some frogs and lizards can endure partial freezing, but fish and mammal cells can’t survive the damage caused by ice crystals. While researchers have known for decades that some cold-water fish have this antifreeze-producing ability, the variegated snailfish has the highest level of gene expression for the proteins ever reported.

The team looked at the species’ genome – the fish’s genetic material – and the animal’s transcriptome, which indicates the proteins it is making at that point in time.

at the University of Illinois who was not involved in the work says she would like to see the team assess levels of antifreeze protein present in the fish’s blood, rather than rely on instructions coded in the species’ genes. While the snailfish’s genes contain the instructions for protein production, it’s unclear how that translates to the animal’s antifreeze ability.

As climate change leads to increased temperatures near the poles, Gruber worries that the cold-water-loving species could be pushed out of their habitat as species suited to more temperate waters move in.

“You literally feel like you’re in a freezer that had been left open overnight,” says Gruber, describing the melting landscape. “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.”

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