The goldfish is a freshwater fish that are often misunderstood. They are one of the earliest fish to be domesticated as pets and are the most common fish kept in an aquarium. This fish is a small member of the carp family. Goldfish are basically a domesticated version of the carp that are native to eastern Asia. First domesticated in China over a thousand years ago, there are many distinct breeds that have since been developed. They vary in size, shape, fin type and color.