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Conservation status: Least concern
| A Hama Nishiki goldfish (a relation of the Pearlscale fancy goldfish variety)|
A Hama Nishiki goldfish (a relation of the Pearlscale fancy goldfish variety)
| Carassius auratus auratus|
The goldfish, Carassius auratus, was one of the earliest fish to be domesticated, and is still one of the most commonly kept aquarium fish and water garden fish. A relatively small member of the carp family, the goldfish is a domesticated version of a dark-gray/brown carp native to East Asia. It was first domesticated in China and introduced to Europe in the late 17th century.
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; few goldfish reach even half this size. 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. A group of goldfish is known as a troubling.
Selective breeding over centuries has produced several color variations, some of them far removed from the "golden" color of the originally domesticated fish. Goldfish may also lose their "golden" color, or rather any goldfish color, by being kept in a dark room, this causes the scales to turn white. There are also different body shapes, fin and eye configurations. Some extreme versions of the goldfish 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.
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 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 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. They also die without eating in a week.
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.
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 belief that goldfish have a three second memory has been proven completely false. 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, colours 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. 
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. Auditory responses from a blind goldfish proved that he recognized one particular family member and a friend by voice, or vibration of sound. This behavior was very remarkable because it showed that he recognized the vocal vibration or sound of two people specifically out of seven in the house.
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 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 predators 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.
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, 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.
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[How to reference and link to summary or text], their presence in an aquarium can be quite a problem[How to reference and link to summary or text]. 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[How to reference and link to summary or text] 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.
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 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[How to reference and link to summary or text]. 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[How to reference and link to summary or text].
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.[How to reference and link to summary or text]
Several closely related species also have orange varieties:
- ↑ Background information about goldfish. URL accessed on 2006-07-28.
- ↑ , 
- ↑ Fishtalk from The Profishionals, Autumn 2001 (PDF). URL accessed on 2006-07-21.
- ↑ San Diego Zoo's Got Questions? Animal Group Names. URL accessed on 2007-02-04.
- ↑ GuinnessWorldRecords.com, 2003, retrieved on: July 14, 2007
- ↑ The Times 01 October 2003 - Goldfish pass memory test. URL accessed on 2006-08-21.
- ↑ Lloyd, J & Mitchinson, J: "The Book of General Ignorance". Faber & Faber, 2006.
- ↑ http://www.chinaculturemall.com/Crafts/article.aspx?id=4831
- ↑ Fish School. URL accessed on 2006-07-21.
- ↑ http://www.mypets.net.au/flex/goldfish/528/1
- ↑ Information on Mosquito Prevention and Control in Fish Ponds. URL accessed on 2006-07-28.
- ↑ Gold fish as invasive species
- “Goldfish Varieties and Genetics: A Handbook for Breeders” by Joseph Smartt, Publisher: Blackwell Science (July 30, 2001), 216 pages ISBN 0852382650 and ISBN 978-0852382653
- Carassius auratus (TSN 163350). Integrated Taxonomic Information System. Accessed on 5 October 2004.
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