Question

Fishes survive in ponds even when the atmospheric temperature is below zero degree celsius explain

Answer 1

it is because the temp. of water is increased as we go in depth so the fishes survive in water in low atmospheric temperature also.

Answer 2

The density of the water is maximum at 4 degree Celsius. During cold season when pond water starts to freeze, water having more density goes to the bottom and water at 0 degree Celsius starts to freeze at the top most layer. And it takes much time to freeze another layer of water under already freezed water.
So fish can easily live in that water.