Conservation status: Secure
The Goldfish (Carassius auratus) was one of the earliest fish to be domesticated, and is still one of the most commonly kept aquarium fish. A relatively small member of the carp family (which also includes the koi carp and the crucian carp), the goldfish is a domesticated version of a dark-gray/olive/brown carp native to east Asia (first domesticated in China) that was introduced to Europe in the late 17th century. The mutation that gave rise to the goldfish is also known from other cyprinid species, such as common carp and tench.
Goldfish may grow to a maximum length of 23 inches (59 cm) and a maximum weight of 9.9 pounds (4.5 kg), although this is rare; most individual goldfish grow to under half this size. In optimal conditions, goldfish may live more than 20 years (the world record is 49 years); however, most household goldfish generally only live six to eight years.
During the Tang Dynasty, it was popular to raise carp in ponds. As the result of a dominant genetic mutation, one of these carp displayed "gold" (actually yellowish orange) rather than silver coloration. People began to breed the gold variety instead of the silver variety, and began to display them in small containers. The fish were not kept in the containers permanently, but would be kept in a larger body of water, such as a pond, and only for special occasions at which guests were expected would they be moved to the smaller container.
In 1162, the empress of the Song Dynasty ordered the building of a pond to collect the red and gold variety of those carp. By this time, people outside the royal family were forbidden to keep goldfish of the gold (yellow) variety, yellow being the royal color. This probably is the reason why there are more orange goldfish than yellow goldfish, even though the latter are genetically easier to breed. 
As time passed, more mutations occurred, producing new color variations, and fancier varieties of goldfish were developed. The occurrence of other colors was first recorded in 1276. The first occurrence of fancy tailed goldfish was recorded in the Ming dynasty. In 1502, goldfish were introduced to Japan, where the Ryukin and Tosakin varieties were developed.
In 1611, goldfish were introduced to Portugal and from there to other parts of Europe. Goldfish were first introduced to North America in 1874 and quickly became popular in the United States.
Varieties of domesticated goldfish
Selective breeding over centuries has produced several color variations, some of them far removed from the "golden" color of the originally domesticated fish. There are also different body shapes, fin and eye configurations. Some 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. However, some variations are hardier, such as the Shubunkin. The main varieties are:
Chinese Goldfish classification
In Chinese goldfish keeping, goldfish are classified into 4 main types, which are not commonly used in the west.
- Dragon Eye - Goldfish with extended eyes, e.g. Black Moor, Bubble Eye, and Telescope Eye
- Egg - Goldfish without a dorsal fin. e.g. Lionhead (note that a Bubble Eye without a dorsal fin belongs to this group)
- Wen - Goldfish with dorsal fin and a fancy tail. e.g. Veiltail ("Wen" is also the name of the characteristic headgrowth on such strains as Oranda and Lionhead)
- Ce (may also be called "grass") - Goldfish without anything fancy. This is the type that is usually used in Japanese carnivals, especially for "goldfish scoops".
- Jikin and Wakin - Goldfish with double tails, but with the body shapes of comets.
Goldfish in ponds
Goldfish are popular pond fish, since they are small, inexpensive, colourful, and very hardy. In a pond, they may even survive if brief periods of ice form on the surface, as long as there is enough oxygen remaining in the water and the pond does not freeze solid.
Common goldfish, London and Bristol shubunkins, Jikin, Wakin, comet and sometimes fantail can be kept in a pond all year round in temperate and subtropical climates. Moor, veiltail, oranda and lionhead are only safe in the summer.
Small to large ponds are fine though the depth should be at least 80 cm (30 in) to avoid freezing. During winter, goldfish will become sluggish, stop eating, and often stay on the bottom of the tank. This is completely normal; they will become active again in the spring. A filter is important to clear waste and keep the pond clean. Plants are essential as they act as part of the filtration system, as well as a food source for the fish. Plants are furthermore beneficial since they raise oxygen levels in the water.
Compatible fish include rudd, tench, orfe and koi, but the latter will require specialized care. Ramshorn snails are helpful by eating any algae that grows in the pond. It is of great importance to introduce fish that will consume excess goldfish eggs in the pond, such as orfe. Without some form of population control, goldfish ponds can easily become overstocked. Koi may also interbreed to produce a sterile new fish.
Goldfish in aquaria
The goldfish is usually classified as a coldwater fish, and it can live in an unheated aquarium. Like most carp, goldfish produce a large amount of waste both in their feces and through their gills, releasing harmful chemicals into the water. This also happens because goldfish cannot digest an excess of proteins, unlike most tropical fish. Build-up of this waste to toxic levels can occur in a relatively short period of time, which is often the cause of a fish's sudden death. It may be the amount of water surface area, not the water volume, that decides how many goldfish may live in a container, because this determines how much oxygen diffuses and dissolves from the air into the water; one square foot of water surface area for every inch of goldfish length (370 cm²/cm). If the water is being further aerated by way of water pump, filter or fountain, more goldfish may be kept in the container.
Goldfish may be coldwater fish, but this does not mean they can tolerate rapid changes in temperature. The sudden shift in temperature that comes at night, for example in an office building where a goldfish might be kept in a small office tank, could kill them, especially in winter. Conversely, temperatures over 25 °C (77 °F) can be extremely damaging for goldfish (this is the main reason why they shouldn't be kept in tropical tanks).
The popular image of a goldfish in a small fishbowl is an enduring one. Unfortunately, the risk of stunting, deoxygenation, ammonia/nitrite poisoning caused by such a small environment means that this is hardly a suitable home for any species of fish, and some countries have banned the sale of bowls of that type under animal rights legislation.
The supposed reputation of goldfish dying quickly is often due to poor care amongst uninformed buyers looking for a "cheap" pet. The true lifespan of a well-cared-for goldfish in captivity can extend beyond 10 years.
Fancy goldfish are unlikely to survive for long in the wild as they are handicapped by their bright fin colors; however it is not beyond the bounds of possibility that such a fish, especially the more hardy varieties such as the Shubunkin, can survive long enough to breed with its wild cousins. Common and comet goldfish can survive, and even thrive, in any climate in which a pond for them can be created. Introduction of wild goldfish can cause problems for native species. Within three breeding generations the vast majority of the goldfish spawn will have reverted to their natural olive color. Since they are carp, goldfish are also capable of breeding with certain other species of carp and creating hybrid species.
Research by Dr. Yoshiichi Matsui, a professor of fish culture at Kinki University in Japan, suggests that there are subtle differences which demonstrate that while the crucian carp is the ancestor of the goldfish, they have sufficiently diverge to be considered separate species.
Like most fish, goldfish are opportunistic feeders. When an excess of food is offered, they will produce more waste and feces, partly due to incomplete digestion of protein. Overfed fish can sometimes be recognized by feces trailing from their cloaca. Goldfish need only be fed as much food as they can consume in three to four minutes, and no more than twice a day. Extreme overfeeding can be fatal, typically by bursting of the intestines. This happens most often with selectively bred goldfish, which have a convoluted intestinal tract as opposed to a straight one in common goldfish. Novice fishkeepers who have newly purchased ruykin, fantail, oranda, lionhead or other "fancy" goldfish will need to watch their fish carefully for a few days, as it is important to know how much the goldfish will eat in a few minutes of time.
Special goldfish food has a lower protein and higher carbohydrate content. It is sold in two consistencies - flakes that float at the top of the aquarium, and pellets that sink slowly to the bottom.
Goldfish enthusiasts will supplement this diet with shelled peas (with outer skins removed), blanched green leafy vegetables, and bloodworms. Young goldfish also benefit from the addition of brine shrimp to their diet.
Behavior can vary widely both because goldfish are housed in a variety of environments, and because their behavior can be conditioned by their owners. A common misconception that goldfish only have a three second memory has been proven completely false.
Scientific studies done on the matter have shown that goldfish have strong associative learning abilities, as well as social learning skills. In addition, their strong visual acuity allows them to distinguish between different humans. It is quite possible that owners will notice the fish react favorably to them (swimming to the front of the glass, swimming rapidly around the tank, and going to the surface mouthing for food) while hiding when other people approach the tank. Over time, goldfish should learn to associate their owners and other humans with food, often "begging" for food whenever their owners approach.
Goldfish also display a range of social behaviors. When new fish are introduced to the tank, aggressive social behaviors may sometimes be seen, such as chasing the new fish, or fin nipping. These usually stop within a few days. Fish that have been living together are often seen displaying schooling behavior, as well as displaying the same types of feeding behaviors. Goldfish may display similar behaviors when responding to their reflections in a mirror.
Goldfish that have constant visual contact with humans also seem to stop associating them as a threat. After being kept in a tank for several weeks, it becomes possible to "pet" a goldfish on the head, feed it by hand, or even cup a hand around it without it reacting in a frightened manner. Some goldfish have been trained to swim through mazes, push a ball through a hoop, or even swim in a synchronized routine by their owners.
Goldfish have behaviors, both as groups and as individuals that stem from native carp behavior. They are a generalist species with varied feeding, breeding, and predators avoidance behaviours that contribute to their success in the environment. As fish they can be described as "friendly" towards each other, very rarely will a goldfish harm another goldfish, nor do the males harm the females during breeding. The only real threat that goldfish present to each other is in food competition. Commons, comets, and other faster varieties can easily eat all the food during a feeding before fancy varieties can reach it. This can be a problem that leads to stunted growth or possible starvation of fancier varieties when they are kept in a pond with their single-tailed brethren. As a result, when mixing breeds in an aquarium environment, care should be taken to combine only breeds with similar body type and swim characteristics.
Goldfish natively live in ponds, and other slow or still moving bodies of water in depths up to 20 m (65 ft). Their native climate is subtropical to tropical and they live in freshwater with a pH of 6.0–8.0, a water hardness of 5.0–19.0 dGH, and a temperature range of 40 to 106 °F (4 to 41 °C) although they will not survive long at the higher temperatures. They are considered ill-suited even to live in a heated tropical fish tank, as they are used to the greater amount of oxygen in unheated tanks, and some believe that the heat burns them. However, goldfish have been observed living for centuries in outdoor ponds in which the temperature often spikes above 86 °F (30 °C). When found in nature, the goldfish are actually an olive green color.
In the wild, the diet consists of crustaceans, insects, and various plant matter.
While it is true that goldfish can survive in a fairly wide temperature range, the optimal range for indoor fish is 68 to 75 °F (20 to 23 °C). Pet goldfish, as with many other fish, will usually eat more food than it needs if given, which can lead to fatal intestinal blockage. They are omnivorous and do best with a wide variety of fresh vegetables and fruit to supplement a flake or pellet diet staple.
Sudden changes in water temperature can be fatal to any fish, including the goldfish. When transferring a store-bought goldfish to a pond or a tank, the temperature in the storage container should be equalized by leaving it in the destination container for at least 20 minutes before releasing the goldfish. In addition, some temperature changes might simply be too great for even the hardy goldfish to adjust to. For example, buying a goldfish in a store, where the water might be 70 °F (approximately 21 °C), and hoping to release it into your garden pond at 40 °F (4 °C) will probably result in the death of the goldfish, even if you use the slow immersion method just described. A goldfish will need a lot more time, perhaps days or weeks, to adjust to such a different temperature.
Because goldfish like to eat live plants, their presence in an aquarium can be quite a problem. Only a few of the aquarium plant species can survive in a tank with goldfish, for example Cryptocoryne and Anubias species, but they require special attention so that they are not uprooted. Fake plants are often more durable, but the plant branches can often irritate or harm a fish if it comes in contact with them.
Goldfish, like all cyprinids, lay eggs. They produce adhesive eggs that attach to aquatic vegetation. The eggs hatch within 48 to 72 hours, releasing fry large enough to be described as appearing like "an eyelash with two eyeballs". Within a week or so, the fry begin to look more like a goldfish in shape, although it can take as much as a year before they develop a mature goldfish color; until then they are a metallic brown like their wild ancestors. In their first weeks of existence, the fry grow remarkably fast - an adaptation born of the high risk of getting devoured by the adult goldfish (or other fish and insects) in their environment.
Goldfish can only grow to sexual maturity if given enough water and the right nutrition. However if kept well, they may breed indoors. Breeding usually happens after a significant change in temperature, often in spring. Eggs should then be separated into another tank, as the parents will likely eat any of their young that they happen upon. Dense plants such as Cabomba or Elodea or a spawning mop are used to catch the eggs.
Most goldfish can and will breed if left to themselves, particularly in pond settings. Males chase the females around, bumping and nudging them in order to prompt the females to release her eggs, which the males then fertilize. Due to the strange shapes of some extreme modern bred goldfish, certain types can no longer breed among themselves. In these cases, a method of artificial breeding is used called "hand stripping". This method keeps the breed going, but can be dangerous and harmful to the fish if not done correctly.
Like some other popular aquarium fish, such as the guppy, goldfish and other carp are frequently added to stagnant bodies of water in order to reduce the mosquito populations in some parts of the world, especially to prevent the spread of West Nile Virus, which relies on mosquitoes to migrate. However, the introduction of goldfish has often had negative consequences for local ecosystems.
Edibility and cruelty
Although edible, goldfish are rarely eaten. A fad among North American college students for many years was swallowing goldfish as a stunt and as an initiation process for fraternities. The first recorded instance was in 1939 at Harvard University. The practice gradually fell out of popularity over the course of several decades and is no longer continued.
In many countries, the operators of carnivals and fairs commonly give goldfish away in plastic bags as prizes for winning games. In the United Kingdom, the government proposed banning this practice as part of its Animal Welfare Bill, though this has since been amended to only prevent goldfish being given as prizes to unaccompanied minors. However, in Rome, Italy, the city passed a law in late 2005, which banned the use of goldfish or other animals as carnival prizes. Rome has also banned the keeping of goldfish in "goldfish bowls", on the premise that it's cruel to the fish to live in such a small, confined space.
Killing fish humanely for human consumption or benign purposes (such as putting down an ill fish) is still legal in most countries (provided that the fish is not a protected fish caught in the wild, a fish in protected reserves or in water where the person concerned has no right to collect the fish). In the United Kingdom, it is illegal to sell live fish (including goldfish) as "feeder fish" for consumption by other animals.
- List of freshwater aquarium plant species for plant species compatible with a goldfish
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- The Common Goldfish by Les Pearce
- Background information about goldfish
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- Article on the oldest Goldfish, Goldie.
- Goldfish Pages - Hobbyists web site that provides information on goldfish standards, goldfish varieties and goldfish care.
- Goldfish varieties: Page 1 Page 2
- Bristol Aquarists' Society - Photographs and descriptions of the different goldfish varieties
- Goldfish Genetics - A resource on the genetics of the goldfish with a focus on the originator, crucian carp, and how their basic genetic package gave rise to the varieties of modern goldfish.