The only fish I lost over winter were a couple small koi fry. Spring is usually the worst time for losing fish; that's when we lost one of our big koi two years ago.
We keep the falls and pump running all winter... we put the de-icers in as needed on really harsh days... and before winter hits I do the best I can to keep leaves out of the pond. I also stop feeding the fish around Columbus Day (it was a little later than that this year as we had a very mild autumn). The koi generally let me know--they lose interest in the food really fast as soon as the temperatures start dropping.
We keep the falls and pump running all winter... we put the de-icers in as needed on really harsh days... and before winter hits I do the best I can to keep leaves out of the pond. I also stop feeding the fish around Columbus Day (it was a little later than that this year as we had a very mild autumn). The koi generally let me know--they lose interest in the food really fast as soon as the temperatures start dropping.