If your pond is too cold to introduce new fish, it's a good idea to keep them inside until the springtime. Check your pond's temperature before purchasing any fish that you intend to add to the water. If it has already reached 50 degrees F, then it's probably a better idea to wait until the spring to add new fish.
If you already have your new fish and the water is too cold to release them, keep them indoors until spring arrives. This will protect them from extreme cold and temperature fluctuations they haven't acclimated for yet. Remember that if the water temperature where your fish is staying is warm enough to keep them from hibernating, that they will continue to need food and grow over the winter.
