About the Common Goldfish
Common goldfish or hibuna are a type of goldfish with no other modifications from their ancestors other than their colour. Most varieties of fancy goldfish were derived from this simple breed. Common goldfish come in a variety of colours including red, orange/gold, white, black and yellow or “lemon” goldfish.
Common goldfish are social animals who prefer living in groups. They are able to interact with any fish belonging to the same species. With provision of adequate care and attention, common goldfish can become tame. Once familiar with the face of its owner, swimming towards the fish keeper during feeding time can be observed and hand-feeding becomes possible. Small goldfish will normally avoid any form of human contact. However, this fear ceases in a middle-sized and mature goldfish. A full-grown goldfish is more likely to eat directly from the hands of its owner without evident hesitation. While this behavior is welcomed by goldfish owners, it proved problematic in outdoor ponds where predators may eat such friendly prey. Mature goldfish will also explore their surroundings through nibbling or grazing behavior.
Read more about the common goldfish at Wikipedia.