Why do goldfish live in the pond?
Goldfish are freshwater fish and can not survive in saltwater environments (oceans, etc) They can only survive in freshwater (non saltwater such as ponds, rivers, and lakes).
Yes, the rate at which a goldfish grows, and its overall size, is often partially determined by its environment. This is why pond goldfish are considerably larger than aquarium goldfish, and why goldfish that are cramped-up in bowls stay relatively small. If you want your goldfish to grow into large healthy fish you'll buy them a large aquarium or pond to live in.