How low of a temperature can a goldfish survive? I've heard that they can actually freeze, or mostly, and still live. I know somebody who let their fish freeze, accidentally, in the recent cold snap, and I'm trying to help save them. Thanks!
Goldfish cannot survive being frozen. Although this depends on the variety of goldfish, they should, however, be able to survive the pond freezing over, so long as it doesn't freeze all the way to the bottom.
Ice actually insulates the fish from excessive cold, so any of the water below the ice won't be colder than 32F.
My parents have koi and goldfish in their pond, and in the beginning my dad didn't keep the pond open (I should add, this pond is a half acre, and 15 feet deep) so it froze over every year--enough to carry a foot of snow, a snowblower, and two girls ice skating on it very safely. The fish were fine every year, until the one year it froze too deep--that year it killed the bluegill and the bass as well, so it was a really severe freeze.
The water in the pond is probably around 40 degrees in fall and spring, so goldfish and koi can definitely survive pretty low; actual freezing of the fish though I'm sure will be fatal. If bringing up from 35-40 degrees it should obviously be done slowly.
Let me beg to differ on goldfish not surviving being frozen, not that I intend to allow mine to freeze.
BUT, my grandfather was a magician and during the depression he travelled by car in Michigan. Many times sleeping in their car in the cold winter. In one of their acts they used a goldfish.
On some nights it would be cold enough to freeze the fish in the water. When they began to drive,the car would warm, the fish would thaw, and wala...it was alive
But don't freeze your fish. I used narrators and a trough heater on my outside tank