if its a private pond cut off from main waters completely and legal
large muskies, pikes would be great, they'd get huge and great for fishing
exotics, like silurus glanis the wels cat, gets to 15 feet long, and can winter just fine
toothy
bagarius yarelli, goonch, would get about 6 feet, 200 pounds, world record and swallow local dogs that go for summer dips
masheers, tor sp. , barbs that will eat smaller fish, and grow huge too, 70-150 pounds are not uncommon and can take cold waters. just a few ideas...I would love to be where you're at!