A species of tiny fish, the variegated snailfish (Liparis gibbus), lives in the icy cold waters off Greenland. Incredibly, they’re able to avoid freezing solid and survive in these sub-zero temperatures by producing antifreeze proteins inside their bodies.
Scientists have known about these kinds of antifreeze proteins since the 1970s, but according to a new study the snailfish takes the crown when it comes to producing them – their genes have the highest expression levels of antifreeze proteins ever observed.
It’s not all that makes this tiny fish extraordinary.
Researchers decided to investigate antifreeze proteins only after encountering another of its exceptional abilities: biofluorescence – they glow green and red.
But the authors warn that these highly specialised fish could face a significant threat in the future from warming oceanic temperatures due to climate change. The research has been published in the journal Evolutionary Bioinformatics.
“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, such as antifreeze proteins, which prevent ice crystals from forming,” says co-author David Gruber, a research associate at the American Museum of Natural History and a distinguished professor of Biology at the City University of New York in the US.
“We already knew that this tiny snailfish, which lives in extremely cold waters, produced antifreeze proteins, but we didn’t realise just how chock-full of those proteins it is – and the amount of effort it was putting into making these proteins.”
Unlike some species of reptiles and insects, fishes aren’t able to survive their body fluids even partially freezing. Despite this, some can still survive in the extreme environments of the polar oceans thanks to the production of antifreeze proteins inside their bodies.
Antifreeze proteins were first discovered in Antartic fish in a 1971 study, but have since been found to have evolved independently in many different organisms: from bacteria, to plants, lichens, insects, and vertebrates.
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These proteins don’t work exactly like conventional antifreezes, for instance the ones you put into car’s cooling system, which work by dissolving in the water and lowering its freezing point.
Instead, they limit the growth of ice crystals to manageable sizes by binding to them.
There are five different classes of fish antifreeze proteins produced by five different gene families, which are primarily produced in the liver and then exported to the blood.
In a 2019 expedition Gruber and co-author John Sparks, who is a curator and professor in the Department of Ichthyology at the American Museum of Natural History, found that snailfish is the only polar fish reported to biofluoresce.
These snailfish genes have the highest expression levels of antifreeze proteins ever observed, among the top one percent of expressed genes in the fish.
The finding highlights just how important the antifreeze proteins are to the snailfish’ survival, but also raises a red flag as to how they’ll fare in a warming world.
“Since the mid-20th century, temperatures have increased twice as fast in the Arctic as in mid-latitudes and some studies predict that if Arctic sea ice decline continues at this current rate, in the summer the Arctic Ocean will be mostly ice-free within the next three decades,” concludes Sparks.
“Arctic seas do not support a high diversity of fish species, and our study hypothesises 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.”