Do fish get cold? How Fish Survive Winter

Mar 15, 2021 | 3 minute read
Reading Time: 3 minutes

If you’ve ever been ice fishing or even got caught out in the rain, you know that water gets pretty darn chilly in winter. You can’t help but wonder how anything can live in such extreme conditions as frozen lakes and icy oceans. Do fish get cold? How do they survive the winter? These are common questions this time of year, so here are the answers.

Do fish get cold?

A walleye fish poking out of a hole in the ice wearing a scarf
“Get me out, it’s freezing!”

Yes, fish are very sensitive to changes in water temperature. So much so, in fact, that even a few degrees difference can sometimes kill them. Fish definitely get cold, the question is what “cold” means to them.

All fish species have a preferred range of water temperature. However, it varies massively depending on where they’re from. A tropical Lionfish might start shivering at around 75°, while a Northern Pike would get heatstroke in water that hot. Both these guys are incredibly hardy, they’re just built for different conditions.

How do fish survive the winter?

The thing to remember about fish is that they’re (mostly) cold-blooded. They don’t have any way of warming themselves up. And on top of that, heat transfers much more quickly in water than in air. However, fish have developed a few tricks to make it through those long winter nights.

Migrate

A school of fish swimming under a wave in the sea
We’re not the only ones who vacation in the sun.

This one’s pretty obvious. If it’s too cold in your local waters, just go someplace warmer. Loads of fish migrate, especially saltwater species. Some travel all over the world, while others just cruise up and down the coast, following their dream bathing conditions.

Of course, fish travel for a variety of reasons. Most follow food or head to their spawning grounds at certain times of year. However, temperature plays a big role in both of these. That’s why you can never be sure when fish will show up each year – it all depends on the weather.

Hibernate

several Koi Carp hibernating in a pond in winter to survive the cold
Sometimes the best thing to do is just go to bed.

Migrating is all fine and dandy, but it’s not always an option. Some fish have nowhere to go, while others simply aren’t fast or strong enough to make the journey. Instead, they have to tough it out as the lake freezes above them or the winter storms churn up chilly water from below. The easiest way to do this? Go to sleep.

Fish don’t actually hibernate – at least, not in the true meaning of the word. Instead, they enter a state called “torpor.” This is like a deep sleep, where their bodies slow and they stop actively feeding. Some even bury themselves in mud to keep warm. However, they can still wake up if they sense danger or an easy meal passes their way.

Innovate

An Opah, the only warm-blooded fish species on earth
Opah’s looks aren’t even the weirdest thing about them.

As the saying goes: “if you can’t beat ‘em, join ‘em.” Some fish are just used to the cold, and can get by just fine even in the depths of winter. Sub-zero specialists like Arctic Char are perfectly happy in near-freezing temperatures. In fact, their bodies are actually specially adapted to not freeze.

Then there are the real piscatorial pioneers like Bluefin Tuna. These apex predators are actually able to warm their blood, keeping their eyes alert and muscles strong so they can hunt in colder seas. Opah went a step further, becoming the only fully warm-blooded fish in the world. And you thought their looks were the weirdest thing about them!

The truth is that most fish use a combination of all three of these tactics. They might migrate to the bottom of a lake where the temperature’s stable, then sleep off the worst of the February blues. Opah are warm-blooded, but they still roam the oceans following their ideal conditions. Winter underwater is tough, and fish need every trick in the book to stay alive.

Got any winter fishing questions, or a fun fish fact to share? Drop us a comment below – we’re always happy to learn more about the weird world beneath the waves!

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