The goldfish (Carassius auratus) is a freshwater fish. It was one of the earliest fish to be domesticated, and is one of the most commonly kept aquarium fish.A relatively small member of the carp family (which also includes the koi carp and the crucian carp), the goldfish is a domesticated version of a less-colorful carp (Carassius auratus) native to east Asia. It was first domesticated in China more than a thousand years ago, and several distinct breeds have since been developed.