Welcome to Canada, where the winters never seem to end!

It’s near the end of February, but we may still have a way to go before spring arrives to free us from this bitter cold. Thankfully we Canadians have come up with a few helpful ways to stay warm during this long chilly season: fluffy coats, wool socks, long underwear, lots of warm beverages, you name it!

But what about the fish? How can they possibly tolerate these harsh winters?

They don’t wear coats, they don’t have houses with central heating, they can’t even regulate their own body temperature! Fish are poikilotherms, meaning their internal body temperature is largely dependent on the temperature of their environment. That’s bad news if you’re a fish and your environment is negative 20°C. But don’t fret my fish-loving friends! These scaly animals have come up with some pretty interesting ways to beat back the chill.


Imagine if you could produce a protein that flowed through your blood and kept your heart from turning into a popsicle. Well, fish like the Atlantic cod, the winter flounder, and the sea raven have such a magical molecule! As soon as ice crystals begin to form in their blood, these antifreeze proteins will coat it and prevent it from growing. This handy little adaptation has allowed these fishes to survive their frigid ocean home by preventing their tissues from being damage by frost.



You know how you constantly have to salt your driveway in the winter to melt the ice? Well, fish have also figured out that salt is pretty handy for preventing themselves from freezing! In fact, salt water has a freezing point of about negative 2°C, which is two degrees more than fresh water. Many fish will have very high concentrations of electrolytes (salts), glycerol, and sugars in their body to stay ice-free.

Bottom of the Lake

We talked about chemistry, now let’s do a little physics. Ice is less dense than liquid water, which is most dense at 4°C. So when our lakes freeze over, the ice floats at the top, leaving the liquid water underneath that goes from 0 to 4 degrees the deeper it gets. This allows most fresh water fish to survive simply by staying at the bottom-most part of the lake.

Let’s take the walleye as an example. When the cold weather hits, this big tasty fish goes into a resting state while staying near the muddy or sandy bottom of the lake. Its metabolic activity – all the chemical reactions the happen inside its cells – is reduced, as is its need for food and oxygen. It’s a good thing they don’t need as much oxygen, because there will be a limited supply in the frozen lake, since ice at the top prevents any more of it in the air from dissolving into the water.

So there you have it! Canadian fish are just as amazingly adept at living through the winter as Canadian people, although they complain a heck of a lot less. So next time you think you can’t possibly survive another day in this snow globe of a country, remember the fish: if they can make it, so can you!

Have a question about the Aquarium, or something you would like to see on Deep Sea Diary? Comment below for the chance for your question to be featured in our monthly Q&A post!


Patrick works in education and conservation at Ripley’s Aquarium of Canada. He has a strong interest in evolution, which reflects his research background in molecular evolution. He decided to leave the academic world to focus on his communication skills to teach people about two subjects that are also close to his heart: aquatic life and environmental protection.

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