When we had goldfish in the pond, I don't think we ever lost any babies to the Winter, just to the snapping turtle that was living in there without our knowledge. There are still over 50 baby koi in my pond and 50, or so, in a tank in the house. I can see the difference in the ones that are in the pond as they are more colorful and larger.
Just checked Craigslist for my area and the only people that are advertising Koi, don't even live close to this area. Maybe I'll have a good chance to sell them on Craigslist. Just don't want any weird people coming to my house......OH, I know!! We can meet them in the Big M parking lot to make the deal!