Goldfish (Carassius auratus)

Goldfish (Carassius auratus)

The Goldfish (Carassius auratus) is small freshwater fish that was one of the earliest fish to be domesticated. It has been developed into many ornamental breeds and is still one of the most commonly kept fish in aquariums and outdoor water gardens.

The goldfish is a domesticated version of the Prussian carp (Carassius gibelio), a dark-gray/brown carp native to Asia. It was first bred for color in China over 1,000 years ago. Due to selective breeding, goldfish are now found in various colors, color patterns, forms and sizes far different form those of the original domesticated carp.


In China during the Tang Dynasty (618 - 907), it was popular to raise carp in ponds. As the result of a dominant genetic mutation, some 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 much smaller container.

In 1162, the Empress of the Song Dynasty ordered the construction of a pond to collect the red and gold variety of those carp. By this time, people outside the imperial family were forbidden to keep goldfish of the gold (yellow) variety, yellow being the imperial color. This is probably the reason why there are more orange goldfish than yellow goldfish, even though the latter are genetically easier to breed.

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. During the 1620's, goldfish were highly regarded in Southern Europe because of their metallic scales, and were known to symbolize good luck and fortune. It became tradition for married men to give their wives a goldfish on their first year anniversary, as a symbol for the prosperous years to come. This tradition quickly died, as goldfish became more available around Europe, thus losing their sacred status. Goldfish were first introduced to North America around 1850 and quickly became popular in the United States.


Goldfish are a relatively small member of the Cyprinidae family. The Cyprinidae or carp family is the largest family of freshwater fishes in the world, and may be the largest family of vertebrates. Apart from the goldfish, well-known members include the minnow, chub, shiner, zebrafish, common carp and koi.

Selective breeding over centuries has produced many different color variations, some of them far removed from the 'golden' color of the original goldfish. There are also different body shapes, fin and eye configurations. Some extreme versions of the goldfish need to be kept in an indoor aquarium as they are much less hardy than varieties closer to the "natural" original. However, some varieties such as the Shubunkin are hardier, and can be kept in outdoor pools.

Goldfish may also change their color by varying the spectrum of light under which they are kept. Goldfish produce pigment in response to light. Cells called chromatophores produce pigments that reflect light, and gives coloration. The color of a goldfish is determined by which pigments are in the cells, how many pigments molecules there are, and whether the pigment is grouped inside the cell or is spaced throughout the cytoplasm. If a goldfish is kept in the dark it will appear lighter in the morning, and over a long period of time will lose its color.

Goldfish can grow to a maximum length of 22 inches (58.42 cm) and a maximum weight of 9.9 pounds (4.5 kg), although this is rare; few goldfish reach even half this size. The longest goldfish measured was 47.4 cm (18.7 in) from snout to tail-fin end in Hapert, The Netherlands. The longest fancy goldfish measured was an oranda called Bruce. It was measured at 37.2 cm (15 in) in 2002. Bruce has since died but not before attaining an additional 2.8 cm, making Bruce's length in excess of 40 cm.

In optimal conditions, goldfish may live more than 20 years, but most household goldfish generally live only six to eight years. The oldest recorded goldfish lived to 49 years, but most household goldfish generally live only six to eight years, due to being kept in bowls.

The collective noun for a group of goldfish is a 'troubling' of goldfish.


Rare varieties

  • Tosakin or curly fantail goldfish
  • Jikin or peacock tail goldfish
  • Shukin
  • Tamasaba or sabao
  • Meteor goldfish
  • Egg-fish goldfish
  • Curled-gill goldfish or reversed-gill goldfish
  • Mirror-scale goldfish

Chinese classification

Goldfish are classified into 4 main types by Chinese tradition. These classifications 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.

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 pond. 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 further 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.

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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, like other cyprinids, lack a stomach and only have an intestinal tract, and thus 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. However, because of their large oxygen needs and high waste output, the popular goldfish bowls of the past are not appropriate housing for goldfish.

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. Temperatures under about 10°C (50°F) are dangerous to fancy varieties of goldfish, though commons and comets can be exposed to these temperatures without a problem. While extreme high temperatures (over 82°F) can be harmful they can actually be beneficial for fighting protozoan infestations by accelerating the parasite's life-cycle, thus eliminating it more quickly. The optimum temperature seems to be around 75°F.

The popular image of a goldfish in a small fishbowl is an enduring one. However, some countries have banned the sale of bowls of that type under animal rights legislation due to the risk of stunting, deoxygenation and ammonia/nitrite poisoning in such a small environment. Like all fish that are kept as pets, goldfish do not like to be petted. In fact, touching a goldfish can be quite dangerous to its health, as it can cause the protective slime coat to be damaged or removed, which opens the fish's skin up to infection from bacteria or parasites in the water. However, goldfish will respond to pet owners by coming to the surface of the water at feeding time, and can be trained or acclimated to taking pellets or flakes from a human's fingers.

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, could 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 diverged to be considered separate species.

If left in the dark for a period of time, a goldfish will turn almost gray. Goldfish have pigment production in response to light, which is almost like our tanning in the sun. Fish have cells called chromatophores that produce pigments which reflects light, and gives colouration. The colour of a goldfish is determined by which pigments are in the cells, how many pigments molecules there are, and whether the pigment is grouped inside the cell or is spaced throughout the cytoplasm. So if a goldfish is kept in the dark it will appear lighter in the morning, and over a long period of time will lose its colour.


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 one to two minutes, and no more than three times a day. Contrary to some common belief, extreme overfeeding will not increase the size of the fish but can actually 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 ryukin, 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 couple minutes of time.

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 live food such as daphnia and bloodworms. Young goldfish also benefit from the addition of brine shrimp to their diet. As with all animals, individual goldfish will display varied food preferences. In any case, it is better to feed them a variety of foods listed above.


In 1994, a public experiment at the Palais de la Decouverte science museum showed that goldfish could be trained to recognize and to react to light signals of different colors by using positive reinforcement. More recent research by the School of Psychology at the University of Plymouth in 2003 demonstrated that goldfish have a memory-span of at least three months and can distinguish between different shapes, colors and sounds. They were trained to push a lever to earn a food reward; when the lever was fixed to work only for an hour a day, the fish soon learned to activate it at the correct time. The Discovery Channel's popular show Mythbusters tested the myth that goldfish only had a memory span of 3 seconds and were able to prove that goldfish had a longer memory span than commonly believed. The experiment involved training the fish to navigate a maze. It was evident that they were able to remember the correct path of the maze and that they therefore had a memory span of over three seconds. A study at the start of the 2000's showed that fish do actually respond to certain colours, this is most evident when it comes to feeding as fish are also aware of feeding times provided they are fed at around the same time everyday.


Behavior can vary widely both because goldfish are housed in a variety of environments, and because their behavior can be conditioned by their owners.

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 specific 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. Auditory responses from a blind goldfish proved that it recognized one particular family member and a friend by voice, or vibration of sound. This behavior was remarkable because it showed that the fish recognized the vocal vibration or sound of two people specifically out of seven in the house. Goldfish are gregarious fish that show 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, sometimes months, it becomes possible to feed a goldfish by hand 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 predator avoidance behaviors 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.

Native environment

Goldfish natively live in ponds, and other still or slow 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,preferably a pH of 7.5, a water hardness of 5.0-19.0 dGH, and a temperature range of 40 to 90°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 plants.

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 30 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, the presence of goldfish in a planted aquarium can be quite a problem. Only a few aquarium plant species can survive in a tank with goldfish, for example the Cryptocoryne and Anubias species, but they require special attention to ensure they are not uprooted. Artificial plants made of plastic are often more durable, but might irritate or harm a fish's skin if it comes in contact with the plants. Artificial plants made of silk are a reasonable alternative.


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.

Some scientists believe goldfish can only grow to sexual maturity if given enough water and the right nutrition. However, if kept well, they may breed indoors, but not in a small fishbowl. 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 their 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. As a result, goldfish are considered a pest in many countries, including the USA.


Although edible, goldfish are rarely eaten except in certain countries. 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 now rare.

In the Belgian city of Geraardsbergen an annual festival is held where the medieval tradition of swallowing a small fish swimming in a cup of wine still survives. There have been a couple of court cases in the last decade but the tradition seems to survive nonetheless. The fish used is often a goldfish because of its size and price.

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. Rome, Italy, 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 is cruel for a fish to live in such a small space.

In the UK, the Animal Welfare Act 2006 prohibits deliberate and "unnecessary suffering" to animals, but contrary to widespread belief, it does not explicitly outlaw the feeding of live feeder fish, such as goldfish, to other fish. However, it does prohibit introducing two animals for the purpose of "fighting, wrestling or baiting". Nonetheless, the assumption is that a legal case could be made to class the use of feeder fish as a "fight" and though as-yet untried in the courts, the risk of such a prosecution has led many retailers and hobbyists simply to treat the use of feeder fish in the UK as illegal.