Why Don't Fish Freeze in Cold Arctic Waters?

If you live in Canada, winter eventually “gets in your veins,” so to speak. But the animal kingdom has one-upped people in this department. There are actually fish that live in the Arctic and Antarctic that have antifreeze running through their veins!

Antifreeze is a substance that keeps a liquid from freezing. It lowers the freezing temperature, so it prevents damage that could be caused by ice formation. For example, if you’ve ever driven or ridden in a car in winter, antifreeze is what’s keeping the liquid in that car’s radiator from freezing.

Fish living in cold climates have evolved an adaptation to keep from freezing: antifreeze proteins. Arctic and Antarctic fish families have these proteins in their blood. They’re part of why these fish can live in waters that other fish can’t.

Did you know?

Because of its salt content, seawater freezes at -2°C, not 0°C.  

Because fish are ectothermic (cold-blooded) animals, when the water they live in is below freezing, they need a way to keep themselves from freezing. This is where the antifreeze proteins come in.

Antifreeze proteins have long strands of repeating amino acid units that can bind to ice crystals. 

Ice crystals are dangerous to the fish because their formation in blood leads to cell death. Small ice crystals can grow larger using surrounding water in the blood. Antifreeze proteins can prevent this by binding to the small crystals. This prevents the crystals from growing, and prevents the blood from freezing. 

Did you know?

Humans have found ways to use antifreeze proteins, too. For example, ice cream manufacturers use them to prevent ice crystals from forming. Scientists and lab workers also use them when they store tissues or organs.

Some of these antifreeze proteins came to be millions of years ago, and have evolved multiple times. They’ve evolved whenever a type of fish has needed to change in order to survive.

Antifreeze proteins are an example of convergent evolution. This is when organisms of different species with no close relations nonetheless develop similar characteristics. This usually happens because they’re trying to survive in similar environmental conditions and because there may only be a limited number of options to solve a problem they encounter.

For example, the Antarctic toothfish and the Arctic cod have no close relatives. They also live very far away from each other, almost on opposite ends of the Earth! But they have both evolved antifreeze proteins. That’s because they both live in environments where, without these proteins, they’d freeze to death.

What does all this mean? Thanks to antifreeze proteins, fish can live in areas where they otherwise couldn’t. What an amazing evolutionary adaptation!