The goldfish is a form of wild carp that has been kept by humans as pets since at least 970 A.D., which is the first recorded instance of keeping and breeding them. The Chinese have developed different varieties of goldfish since then, as have the Japanese shortly thereafter. In 1728 the goldfish was first brought to Europe, and since then it has become an important commercial fish for the aquarium hobby, being bred almost everywhere in the world. Koi are a close relative of the goldfish, and with the burgeoning interest in outdoor ponds, both goldfish and koi are in quite heavy demand.
The little goldfish that are sold as feeder fish at your local fish store or that you used to get at carnivals and fairs is simply the plain ordinary version of the fish, usually called “comets.” Larger fish stores will usually have some of the more common “fancy” varieties, most of which have round globular bodies, longer veil tails and various body colors. There are some with bulbous eyes called moors, and some with eyes that look upward called celestials. Whatever type of goldfish you keep, maintenance is the same.
The goldfish does not like warm water. This fish can, in fact, be kept outside in ponds that freeze on the surface for the winter as long as there is plenty of water beneath the ice. This fish is perfectly happy at room temperatures, provided it does not get too warm. The goldfish eats quite a lot and makes a mess. Therefore, it must not be crowded, and the tank water should have very efficient filtration and aeration. This fish is not at all particular about the water parameters and will adjust to just about any pH or hardness as long as there is no abrupt change. Requiring a diet very high in vegetable matter, this fish should always have some form of vegetable like zucchini or romaine lettuce, or sacrificial aquarium plants, available for the fish to graze upon. Of final but critical importance: give the goldfish plenty of room — at least two or three times what you would normally give to tropical fish. A good rule of thumb is to allow at least 5 gallons of water per inch goldfish.