Goldfish ("Carassius auratus") are a species of domesticated fish. Goldfish are in the carp family. They were domesticated in China during the Tang Dynasty. Goldfish can reach up to 59 cm in size, and 3 kg in weight. However, most goldfish grow to only half that size. In captivity, goldfish can live for up to 30 years. In the aquarium, however, most will die earlier. This is because the aquarium is too small. Goldfish need a lot of space so they have room to swim and so the water does not get dirty too fast. 