If your pond is fairly deep you should be fine at least that far south. The deeper your pond is in the winter the more time it takes to use of oxygen reserves. Do you have any snow on the ice? How thick is the ice and how long has the pond been frozen over? How fertile is the pond? Do you have a major algae bloom most of the year?

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.