I just wanted to let you know I have had comet goldfish for 18 yrs living in a pond I built them in my backyard. One of my goldffish just died and was 18 yrs old and well over 18 inches and about 5-6 lbs. They do grow to very large sizes if given the room. My goldfish pond is 225 gallons and the fish stay outside year round here in Colorado.
I do use a pond heater in winters to prevent the pond from freezing. It keeps the water at 40 degrees F. Just thought you might want to know they do get bigger than 9 inches. I also have a large one that is all black and many small ones that are mostly orange.
Karann thanks for taking the time to write to us, we will be sure to update our webpage Comet Goldfish
