Goldfish

The goldfish (Carassius auratus) is one of the earliest fish to be domesticated and still one of the most commonly-kept aquarium fish. A smallish member of the carp family, the goldfish is native to east Asia.

Part of its popularity is due to the goldfish's hardiness. It is a cold-water fish[?], and can live in an unheated aquarium or in an outdoor fishpond[?]. In a pond, it will even survive brief periods of being iced over.

Selective breeding has produced several colour variations, some of them far removed from the "golden" colour of the original. There are also different body shapes, fin and eye configurations. Such extreme versions of the goldfish do need to be kept in an aquarium -- they are much less hardy than varieties closer to the "wild" original.