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Do Pond Fish Hibernate in Winter?

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As winter rolls around, you might wonder what happens to your pond fish below the snow and ice.

Do fish in ponds hibernate? And how do fish survive in a frozen pond during winter?

In this guide, we'll answer those questions and find out exactly what's going on in your pond during the winter months!

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Do Pond Fish Hibernate in Winter?

Pond fish enter a state of torpor in winter, which is similar to hibernation. As the water temperatures drop, their activity level slows down, and their metabolism is greatly reduced. Torpor is not considered full hibernation, as it is doesn't typically last as long. But, there are similarities, such as a drastically slowed heart rate, metabolism, reaction time, and breathing rate.

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We are referring to cold-blooded pond fish, like koi fish and goldfish, for example. Tropical fish should be removed from your garden pond and placed in a tank or aquarium indoors for the Winter.

In short, torpor allows animals (pond fish in this case) to rest and preserve energy during the cold winter months. This is essentially how pond fish survive in the winter. And you'll notice they really start to slow down when water temperatures reach around 45 to 55 degrees F. Below that, and they become dormant, appearing not to move at all (though they still do, just not much)!

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Some pond fish, like Koi and goldfish, are considered poikilothermic, meaning they are cold-blooded. Their body temperature, and in turn, their bodily functions, are regulated by the temperature of the surrounding water.

So, what do you do with your pond fish in the winter? As long as you've properly winterized your pond, there is very little for you to do other than make sure that your pond doesn't completely freeze over. You can do this by:

  • Making sure your pond is deep enough. Only overwinter fish in a pond that is at least 24" inches deep and preferably deeper. Your pond fish will not survive in a pond if it completely freezes solid. They will need a place to enter torpor, which is usually a warmer pocket of water beneath the ice, near the bottom of the pond.
  • Keeping a hole in the icy surface. Even if your pond doesn't completely freeze solid, you will still need to make sure to keep a hole in the icy surface. A pond de-icer is perfect for this. This allows for proper gas exchange - allowing oxygen to enter the water and harmful gases to escape. If the surface of your pond freezes over, pour warm water on it until a hole forms. Do not pound on the surface to break a hole in the ice. This will only cause unneeded stress for your fish.

By providing the right environment for your koi carp or goldfish, they will enter torpor and safely survive those freezing cold periods in your outdoor pond.

How long your pond fish hibernate will depend on the temperature of the water. In spring, your pond fish will come out of hibernation or torpor when the water temperature regularly stays above 45 to 55 degrees F and gradually gets warmer. It can be a slow wake-up process as the pond temperature slowly rises.

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Keep in mind, if you heat a pond in winter with a pond heater to regulate the temperature and keep it above 50 degrees, your pond fish will not hibernate (enter torpor).

Do You Stop Feeding Pond Fish in Winter?

You should stop feeding your pond fish for the winter when pond water temperatures fall below 40 degrees F. Your fish typically won't eat anyways when the water temperature falls below this since their metabolisms have drastically slowed down.

Any food you feed them will just sink to the bottom of your fish pond, creating a sludge layer and potentially causing water quality issues. And if they do eat during this time, the food may not be digested properly, decaying in their system and causing potential health issues.

Check out our detailed guide titled Do You Need to Feed Pond Fish in the Winter? for additional (and important) information. And you'll need to know when to start feeding pond fish after winter to ensure you have the healthiest, happiest fish possible!