Despite their misleading reputation, goldfish are intelligent animals with highly developed physical traits. Here are 20 things you might not know about this common household pet.

1. Goldfish can live much longer than other types of aquarium fish. Some can live to be as old as 30, but most healthy pet goldfish will live for five to 10 years.
2. There are more than 100 distinct breeds of goldfish, all of which live in cold water.
3. Goldfish do not have stomachs. Instead, certain parts of their intestines break down food and absorb its nutrients. Because they do not have a place in their bodies where food can be stored as it is digested, goldfish should be fed several small meals rather than all at once.
4. Because they naturally tend to live in groups, goldfish do not like to live alone. Ideally, at least two goldfish should be kept in the same tank.
5. Goldfish should not be kept in a small bowl. Instead, they should live in a large tank; a 20-gallon tank for one to four small or medium fish is recommended for first-time fish owners. The large tank makes it easier to maintain healthy water conditions.
6. “Jaws” is the most common name given to a pet goldfish.
7. Goldfish do not have eyelids, so their eyes are always open, even when they sleep. They can also see many colors that human eyes cannot, including ultraviolet and infrared light.
8. A group of goldfish is called a “troubling.”
9. Goldfish have been popular pets for more than 2000 years.
10. The first goldfish came from China. They descended from carp after fish owners began selectively breeding their carp to try to get more fish with a gold color.
11. Goldfish were brought to the United States in the 1800s.
12. As omnivores, goldfish eat insects and other small creatures in the wild. Many pet stores sell food products that can supplement this part of a goldfish’s diet.
13. Goldfish can learn to recognize specific human faces and, if they become completely comfortable with their owners, can even be trained to eat out of a person’s hand.
14. Contrary to popular belief, a goldfish’s memory is much longer than three seconds. They can learn to recognize and keep track of when they can expect to be fed throughout the day.
15. Some goldfish can be taught to respond when their names are called.
16. Goldfish change color naturally for a variety of reasons, such as changes in lighting, water quality, eating certain food or aging. This is fairly normal and is really only cause for concern if the goldfish changes color very suddenly or if the color is not consistent; spots can indicate disease.
17. If a goldfish is left in a dark room, it will eventually turn white.
18. Around the world, there are more than 180 koi and goldfish enthusiast groups and societies.
19. Goldfish can discern differences between songs by different composers.
20. A goldfish named Tish holds the Guinness World Record for being the oldest goldfish. Tish lived for 43 years after being won as a prize at a fair in 1956. After his death in 1999, Tish was buried in a yogurt carton.

Sources:

http://channel.nationalgeographic.com/wild/fish-bowl/articles/fun-fish-facts/

https://www.aspca.org/pet-care/small-pet-care/fish-care

http://thegoldfishtank.com/goldfish-facts/

http://thegoldfishtank.com/goldfish-types-about-types-of-goldfish/

http://thegoldfishtank.com/why-do-goldfish-change-color/

http://www.buzzle.com/articles/214268.html

http://www.ducksters.com/animals/goldfish.php

http://www.biokids.umich.edu/critters/Carassius_auratus/

http://www.findfast.org/facts-about-gold-fish.htm

http://www.myfunnypets.net/articles/interesting-facts-about-goldfish/

http://www.kokosgoldfish.com/Clubs.html

http://news.bbc.co.uk/2/hi/uk/414114.stm

http://www.telegraph.co.uk/news/health/pets-health/10132614/Pet-subjects-can-you-train-goldfish.html

http://www.factslides.com/s-Fish