Sure, it sounds like something out of science fiction: a fish that swims in water colder than the freezing point of its blood. But in the icy waters of Antarctica, this is a reality. Meet the Antarctic notothenioid, a group of fish that have evolved something remarkable: antifreeze blood.

In most animals, blood freezes at around -0.5°C, but the Southern Ocean regularly drops below -1.8°C. To survive this, notothenioid fish produce special antifreeze glycoproteins (AFGPs) in their blood, which bind to tiny ice crystals and stop them from growing. This biological ‘antifreeze’ allows them to move and feed in waters that would otherwise kill most marine life.

One of the most studied species is the blackfin icefish (Chaenocephalus aceratus), which not only has antifreeze proteins but is also the only known vertebrate with no haemoglobin, the protein that carries oxygen in red blood cells. Instead, their blood is clear, absorbing oxygen directly through their skin and gills. While this means their blood carries less oxygen, the oxygen-rich cold waters of Antarctica make up for it.

This adaptation has fascinated scientists because it offers clues about how life might survive in extreme environments, even on other planets.

It’s not just fish that have mastered the cold. Antarctica is home to a unique cast of wildlife, each with its abilities:

Emperor Penguins: The largest of all penguins, emperors huddle together in thousands to conserve warmth during brutal winters. Their tightly packed feathers and a special layer of fat help them endure temperatures as low as -60°C.

Weddell Seals: These deep-diving mammals can stay underwater for over an hour and navigate under thick sea ice using only their whiskers.

Antarctic Krill: Though tiny, krill form the foundation of the Antarctic food chain. Some species can shrink their bodies or delay maturity during times of scarcity, a clever survival strategy.

Snow Petrels: These elegant white birds nest in rock crevices and feed on fish and krill, thriving in windswept, frigid conditions.

The antifreeze fish and their neighbours are perfectly adapted to life on ice. But that delicate balance is now under threat.

As climate change warms the Southern Ocean and reduces sea ice, it disrupts oxygen levels, water salinity, and the entire food chain. Melting glaciers and rising ocean temperatures could make it harder for these fish to survive, especially since they are so finely tuned to cold environments.

Krill populations, a major food source for whales, penguins, and seals, are already declining in some regions. This ripple effect could push larger animals into decline, too.

While we can’t plug the melting glaciers ourselves, we can reduce our carbon footprint (travel, diet, energy use), support global climate agreements, and choose sustainable seafood. We should also stay informed and spread awareness about polar biodiversity.

The creatures of Antarctica may seem distant, but they’re a part of Earth’s shared ecosystem, and their survival is linked to our own.