Goldfish breeds vary greatly in size, body shape, fin configuration, and coloration (various combinations of white, yellow, orange, red, brown, and black are known).

Some of these normally gray or silver species have a tendency to produce red, orange, or yellow color mutations; this was first recorded in Imperial China, during the Jin dynasty (266–420).

[11] During the Ming dynasty (1368–1644), goldfish also began to be raised indoors,[7] which permitted selection for mutations that would not be able to survive in ponds.

[8] During the 1620s, goldfish were highly regarded in southern Europe because of their metallic scales, and symbolized good luck and fortune.

[20] The secretary of the Federation of British Aquatic Societies (FBAS) stated of Goldie's size, "I would think there are probably a few bigger goldfish that people don't think of as record holders, perhaps in ornamental lakes".

[20] In July 2010, a goldfish measuring 16 inches (41 cm) and 5 pounds (2.3 kg) was caught in a pond in Poole, England, thought to have been abandoned there after outgrowing a tank.

Their eggs are adhesive and attach to aquatic vegetation, typically dense plants such as Cabomba or Elodea or a spawning mop.

Within a week or so, the fry begins to assume its final shape, although a year may pass before they develop a mature goldfish color; until then they are a metallic brown like their wild ancestors.

In their first weeks of life, the fry grow quickly—an adaptation born of the high risk of getting devoured by the adult goldfish (or other fish and insects) in their environment.

[33][34] By using positive reinforcement, goldfish can be trained to recognize and to react to light signals of different colors[35] or to perform tricks.

Like most species in the carp family, goldfish produce a large amount of waste both in their feces and through their gills, releasing harmful chemicals into the water.

Buildup of this waste to toxic levels can occur in a relatively short period of time, and can easily cause a goldfish's death.

Active aeration by way of a water pump, filter or fountain effectively increases the surface area agitation.

However, rapid changes in temperature, for example in an office building in winter when the heat is turned off at night, can kill them, especially if the tank is small.

However, higher temperatures may help fight protozoan infestations by accelerating the parasite's life cycle—thus eliminating it more quickly.

In fact, touching a goldfish can endanger its health, because it can cause the protective slime coat to be damaged or removed, exposing the fish's skin to infection from bacteria or water-borne parasites.

However, goldfish respond to people by surfacing at feeding time, and can be trained or acclimated to taking pellets or flakes from human fingers.

Only a few aquarium plant species, such as Cryptocoryne and Anubias, can survive around goldfish, but they require special attention so that they are not uprooted.

Common, London and Bristol shubunkins, jikin, wakin, comet and some hardier fantail goldfish can be kept in a pond year-round in temperate and subtropical climates.

Moor, veiltail, oranda and lionhead can be kept safely in outdoor ponds year-round only in more tropical climates and elsewhere only in summer months.

Like their wild ancestors, common and comet goldfish as well as shubunkin can survive, and even thrive, in any climate that can support a pond.

Enthusiasts may supplement this diet with shelled peas (with outer skins removed), blanched green leafy vegetables, and bloodworms.

Like some other well-known aquarium fish, such as the guppy and mosquitofish, goldfish (and other carp) are frequently added to stagnant bodies of water in an attempt to reduce mosquito populations, which spread the vectors of diseases such as West Nile virus, malaria, and dengue.

However, introducing goldfish has often had negative consequences for local ecosystems,[52] and their efficacy as pest control has never been compared to those of native fishes.

[8] Goldfish kept in bowls or "mini-aquariums" suffer from death, disease, and stunting, due primarily to the low oxygen and very high ammonia/nitrite levels inherent in such an environment.

[56] In comparison to other common aquarium fish, goldfish have high oxygen needs and produce a large amount of waste due to the fact they lack a stomach;[57] therefore they require a substantial volume of well-filtered water to thrive.

In addition, all goldfish varieties have the potential to reach 5 inches (130 mm) in total length, with single-tailed breeds often exceeding 1 foot (0.30 m).

[55] In the United Kingdom, the government proposed banning this practice as part of its Animal Welfare Bill,[58][59] though this has since been amended to only prevent goldfish being given as prizes to unaccompanied minors.

A fad among American college students for many years was swallowing goldfish as a stunt and as a fraternity initiation process.

Some animal advocates have called for boycotts of goldfish purchases, citing industrial farming and low survival rates of the fish.