The goldfish 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 come in many variations with different colors and markings, single-tails, double-tails, various body shapes, head shapes from pointed to square, and various other mutations such as telescoped eyes; however, they all stem from the original stocks developed by Chinese, Korean, and Japanese breeders.

Goldfish grow usually 3 to 5 inches (8 - 13 cm), but may grow to a maximum length of 18 inches (46 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 6 to 10 years, due to being kept in bowls. The longest goldfish was measured at 47.4 cm (18.7 in) from snout to tail-fin end on March 24, 2003 in in Hapert, The Netherlands.
A group of goldfish is known as a troubling.
Gender: Males may have small white spots called tubercles around their gill areas when ready to spawn. Females may be noticeably larger when swelling with eggs and the males may start to chase the females around the tank.

Behavior and 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. Scientific studies 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 recognize the person who feeds them 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. Goldfish like to play and benefit from the exercise, so having two fish is better than one.

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 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 success can be accomplished in 7 steps :

• Partial water changes weekly
• Adequate filtration systems for the tank size
• Temperature of 740F or warmer
• Live plants (Duckweed, Anacharis, Apon, etc-a good addition to their diets)
• Lots of aeration or water movement (non-moving tanks cause problems)
• pH level of at least 7.2
• Salt at the first indication of problems

Family: carp
Common Name(s): Calico Veiltail, Comet, Black Moor, Bubble eye, Lionhead, Ranchu, Oranda, Pearl Scale, Ryukin, Panda, Fantail, Shubunkin (calico), Tosakin, Orange Fantail, Black Fantail, Pompon, Celestial, Telescope, etc
Origin: China originally, then Japan, Asia and the rest of the world.

Tank and water:
Temperature: 40°F - 80°F (5°C - 27°C)
Water Hardness: 5° to 20° dH
pH: 6 - 7.5
Minimum Tank Size: Preferrably a 10 gallon or larger and 10 gallons for each additional goldfish if kept in groups.

Adult Size: Usually 3 to 5 inches (8 - 13 cm), but can get bigger inches
Average Lifespan: 10-30 years