Our family has had a small goldfish pond for around 15 years or so. These fish are frozen over every winter, never fed fish food, and thrive like maniacs! How are they so tolerant???

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20 gallon semi planted:
Filters: top fin 10 and 20 power filters.
Fish: 2 panda cories, 1 peppered Cory, 5 kuhli loaches, and 4 cherry barbs.

Usually fish ponds are deep enough that the fish aren't frozen in the ice but just kind of 'hibernating' in the cold water below. As for feeding, I'm sure they eat bugs that fall in, algae, plant matter. Many people do feed the gold fish in their ponds though - it's usually a good idea. Most gold fish ponds also have filtration on them, which keeps the water clean as well.

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20g and 36g Heavily Planted

It's about 3-4 feet deep, and there is filtration+waterfall. We bought them all only about 1 inch long, the biggest one now is ~4-5 in. long. new babies some times appear, and thrive just as well.

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20 gallon semi planted:
Filters: top fin 10 and 20 power filters.
Fish: 2 panda cories, 1 peppered Cory, 5 kuhli loaches, and 4 cherry barbs.

My mom has had goldies in her small pond for years. When the temp drops the fish go into a dormant state for the winter and revive in spring. They eat the plant matter that grows naturally in the pond, as well as bugs and other "life" that comes around. They thrive the same ways fish thrive in the wild, they know what to do ;)

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"Being ignorant is not so much a Shame, as being unwilling to learn".-- Benjamin Franklin

The only type of fish that I know of that hibernates is a Carp. The will cover themselves in mud and stay that way for most of the Winter. Although Koi/GF are in the Carp family, don't believe they do this. Most fish just slow down. They are cold blooded creatures and their body temp will be the same as the water, which slows their metabolism way down and they don't move too much (some) or need to eat as much.