Feeder Goldfish questions and concerns?

Fish will only grow as big as their tank will let them - my feeder goldfish were in a twenty gallon tank, then moved to a 55 gal. tank - now they are in an old boat (16 foot fibergl) that I made a pond out of, and they are all about 10 plus inches long! Despite the fact that you always see goldfish in fishbowls, that is very misleading - goldfish need a waterpump and filter, because they are incredibly messy fish! Don't name them by their colors now - as they grow they will change colors every so often....my little black and white one is now a beautiful deep orange! 4 fish in a ten gallon tank is fine, but they will only grow so big!