This linguistic confusion is why Americans call the Pennsylvania Dutch Dutch even though they're Germans. To review: this country is the Netherlands, its people are Dutch, they speak Dutch. There is no country called Holland, but there are provinces of North and South Holland.
In clean, uncrowded conditions in tanks or ponds, goldfish grow fast. They can grow to a few inches (1 to 4 inches) within the first year. It really depends on their genetics and living situation. It may take a year or two before they change color from brown to gold or whatever color their parents were.
Tank 1. A 20 gallon tank for a one goldfish, and an additional 20 gallons for each additional goldfish. Mature goldfish average 6 to 8 inches in length and therefore they need a big tank for just one fish.Goldfish also produce more waste than any other fish. 20 gallon tank for a one goldfish, and an additional 20 gallons for each additional goldfish. Mature goldfish average 6 to 8 inches in length and therefore they need a big tank for just one fish.