Gold Fish
Conservation status:Domesticated
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Actinopterygii
Order:Cypriniformes
Family:Cyprinidae
Genus:Carassius
Species:Carassius auratus

Goldfish (re small ornamental freshwater fish that are commonly kept as pets. Goldfish were one of the earliest breed of fish to be domesticated and are still one of the most commonly kept fish in aquariums and outdoor water gardens.
Goldfish were originally domesticated from the Prussian carp a dark greyish brown carp native to Asia. It was first bred for color in China over 1,000 years ago. Due to selective breeding, goldfish have been developed into many distinct breeds and are now found in various colors, color patterns, forms and sizes far different from those of the original domesticated carp.

History
In ancient China, various species of carp had been domesticated and reared as food fish for thousands of years. Some of these normally gray or silver species have a tendency to produce red, orange or yellow color mutations; this was first recorded in the Jin Dynasty (265–420).
During the Tang Dynasty it was popular to raise carp in ornamental ponds and watergardens. Due to a natural 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 an outdoor 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 (apart from red and gold) 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 1620s, 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 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.
The wild form of the goldfish is the Prussian carp. Some sources claim the Crucian carp as the wild version of the goldfish. While they are closely related, they can be differentiated by the following characteristics:
C. auratus have a more pointed snout while the snout of a C. carassius is well rounded.
The wild form of the Goldfish C. gibelio often has a grey/greenish color, while crucian carps are always golden bronze.
Juvenile crucian carp have a black spot on the base of the tail which disappears with age. In C. auratus this tail spot is never present.
C. auratus have fewer than 31 scales along the lateral line while crucian carp have 33 scales or more.

Description
The goldfish has a fairly self explanatory name: "gold" describing its color, and "fish" describing its species. Goldfish are a relatively small member of the Cyprinidae or carp family. The Cyprinidae family is the largest family of freshwater fishes in the world. Apart from the goldfish, other well-known members include the minnow, chub, shiner, zebrafish, various Asian carps 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 indoor aquariums 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 about 18.7 inches (47 cm) and a maximum weight of about 10 pounds (4.5 kg). However, this is rare, few goldfish reach even half this size. The longest goldfish measured was 47.4 centimetres (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 40 centimetres (16 in) in Hong Kong, in 2002.
In optimal conditions, goldfish may live more than 20 years, but most household goldfish generally live less than six to eight years, due to sub-optimal living conditions (such as being kept in bowls). The oldest recorded goldfish lived to 49 years. The collective noun for a group of goldfish is a 'troubling' of goldfish.

Varieties
The Common, Comet, and Shubunkin varieties of goldfish are similar to wild carp (except for colour). They are hardy and can grow to a large size. Other more fancy varieties have been developed.
The main fancy varieties are: Black Moor, Bubble eye, Butterfly tail, Calico, Celestial eye, Fantail, Lionchu, Lionhead, Oranda, Panda Moor, Pearlscale, Pompom, Ranchu, Ryukin, Telescope eye, and Veiltail. Rare fancy varieties include: Tosakin or curly fantail, Jikin or peacock tail, Shukin, Tamasaba or sabao, Meteor goldfish, Egg-fish goldfish, Curled-gill goldfish or reversed-gill goldfish, Mirror-scale goldfish.

Chinese classification
By Chinese tradition, goldfish are classified into five main types:
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.
These classifications are not commonly used in countries outside of East Asia.