Polar Fish Illuminates Use of Antifreeze for Survival

New research has revealed that the only known biofluorescent polar fish protects itself from freezing temperatures by instructing its cells to make high levels of an antifreeze protein. This discovery about the variegated snailfish provides insight into how animals that have adapted to extreme environments might fare in a rapidly changing world.

“This fish has remarkable adaptations that allow it to thrive in an extreme environment,” said John Burns, a senior research scientist at Bigelow Laboratory for Ocean Sciences and lead author on the newly published research. “How much control it has over that process has implications for how well it will fare as waters warm and its glacier habitat disappears.”

Polar marine organisms have had to evolve to cope with freezing temperatures. Fish live in these icy waters but cannot survive any freezing of their body fluids. Some of these fish species have evolved to produce antifreeze proteins to prevent ice from forming in their cells and bodily fluids. This ability was discovered in fish nearly 50 years ago, and a team of scientists have now made progress toward calculating how much antifreeze fish may actually be producing.

In 2019, John Sparks and David Gruber from the American Museum of Natural History were exploring iceberg habitats off the coast of Eastern Greenland when they found an unusual fish in a saltwater pond on top of a glacier. The scientists began to study it, discovered the snailfish could glow green and red, and invited Burns and other colleagues to collaborate. Upon investigation of its genetic code, the team discovered that the snailfish tells its cells to produce remarkably high levels of antifreeze proteins. In addition, they found two different types of genes encoding for antifreeze proteins.

“Using DNA and RNA sequencing we peered into the fish's genetic instructions to see how it survives and how this group of fish is still changing,” Burns said. “The study highlights the impressive resources the fish puts into living in temperatures below freezing.”

The discovery highlights the importance of this survival mechanism, and raises a red flag about how they might fare in warming environmental conditions. In the Arctic, temperatures have increased twice as fast as temperate regions since the middle of the 20th century. Some studies even predict an ice-free Arctic Ocean within the next three decades.

“Arctic seas do not support a high diversity of fish species,” said Sparks, a co-author on the paper. “Our study hypothesizes that with increasingly warming oceanic temperatures, ice-dwelling specialists such as this snailfish may encounter increased competition by more temperate species that were previously unable to survive at these higher northern latitudes.”

Because this study was based one individual snailfish, Burns said it is important to look at additional examples to learn about the species. He wants to conduct further research to understand exactly how much antifreeze is being made and how the levels could change to adapt to different temperatures.

“Snailfish are one of the only types of fish to live both around arctic glaciers and in the deepest depths of the ocean,” Burns said. “What is in the snailfish genetic code that allows them to be successful in such different and extreme environments?”

Photo credit: © John Sparks, David Gruber