I have heard about this being possible, but didn't know if it was true. If you were to have and were maintaining a small, man-made pond in a place such as the upper Midwest in the United States, is it possible for fish to survive over the winter while remaining in the pond? I mean, if it's possible, what do they do? Hibernate?

Does the pond have to be a certain depth? Cubby holes? Types of fish? Certain conditions that need to be met?

Just curious, because I have thought constructing an outdoor pond in which I would like to put some fish. Thank you! :)

How cold does it get where you live?

Gold fish (not round bellies) and koi are the only ones that would survive because they are cold water fish.
In winter their metabolism slows down and they just chill out until spring - not really moving too much.
Most people where I live have at least 24 inches of water, but most are deeper than that.
You would just winterize the pond - kind of like you do a swimming pool.
The air pump is left on, but the filters are shut down, and a screen to keep leaves and debris out is put over the top of it.
They are fed very, very little - a small amount once a week.
If you are in really cold weather where the surface will freeze, there is a device that you'd have to have which gives a breathing hole -
I don't know what it's called though.
We had a really cold winter about 10 years ago where the surface water froze.
My mom put a basket ball in the pond at night and took it out in the morning... it did the trick.

Not much to it in the winter time

How cold does it get where you live?

It could get as low as 20 below zero or even colder. But, that would be a rare thing. Usually in recent years, not down to lower than the teens and some single digits.

Where do you live, Kae? If you don't mind my asking.

South east coast

That's pretty cold - LOL
I don't know about the subzero temps
But with teens and single digits, if the water is deep enough, it shouldn't freeze solid.
The fish will just sink to the bottom where it's not frozen - they look lifeless, but they're fine.

I have heard something about them going into little caves or cubby holes in order to over-winter. Could that also be true?

If you have a cave or cubby in your pond, they will wonder in there from time to time,
But I doubt they would stay the whole winter in there.
They still move and swim around (at least the areas I'm familiar with)
You have a different climate than I do so things could be totally different... Thats something I'd be interested in knowing as well:)...

Well, obviously fish live in wild ponds that freeze over. If the water is deep enough, there will be a layer of ice over a layer of unfrozen water. As I understand it, the cold water decreases the fishes metabolism and thus they can survive on much less food than they need in the warmer months.

Well, obviously fish live in wild ponds that freeze over. If the water is deep enough, there will be a layer of ice over a layer of unfrozen water. As I understand it, the cold water decreases the fishes metabolism and thus they can survive on much less food than they need in the warmer months.
You are right about the metabolism slowing down and how they eat less.

However, we cannot compare wild fish to goldfish and koi or lakes and natural ponds to the ponds we keep in our back yards.

Just let me know if you'd like for me to explain :)

I have an outdoor fish pond which is about 24 inches deep, and my fish do fine over the winter. Granted, I'm in VA, so it doesn't get as cold as you are talking, but from what I have read in pond books, it's a good idea to have 3-feet if possible in the pond. Also, as Kae said, there is a device which keeps the water from freezing over. What we usually do it cover the pond with glass doors and make sort of a fish-greenhouse. We took old sliding glass doors, and build a frame to lay them on over top of the pond. They are placed at an angle so water will run off. The open sides we cover with heavy plastic sheeting, leaving a small gap to feed (which we almost never do) and check to see if the top is frozen over. Additionally, if your pond is in the ground, not built up, the surrounding earth will help to insulate it.