Long lived the Goldfish (Carassius auratus)!  Goldfish were originally domesticated from the Prussian carp (Carassius gibelio), a dark greyish brown carp native to Asia.  It is believed to be first kept in captivity in China around 960-1279 A.D., goldfish has been known as the most popular aquarium fish in the world as they have been kept as pets for centuries. Due to selective breeding over a long period of time, goldfish have been developed into many distinct breeds and are now found in various colors, color patterns, forms and sizes, very much different from those of the original domesticated carp.

Goldfish are coldwater fish, and can live in water close to freezing temperature, although it prefers water temperature to be between 46 and 64 degrees F or 8 to 18 in degrees Celsius. 

A normal goldfish can grow up to about 16 – 20 cm long, but considerably shorter in captive condition in an aquarium. Goldfish may live more than 20 years if kept under good conditions, but most will generally live for less than six to eight years in sub-optimal living conditions such as that in bowls.  The oldest goldfish recorded to have lived is 49 years!

Goldfish will turn almost grey if they are left in the dark for a period of time. Goldfish have cells called chromatophores that produce pigments which reflects light, and gives coloration. 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 color.

Goldfish are opportunistic feeders. They will eat non-stop at many kinds of food and produce wastes and feces trailing from their cloaca. To prevent excessive production of waste from Goldfish, they should only be fed as much food as they can consume within one to two minutes per feeding, and no more than three times a day.

There have been scientific studies conducted on goldfish and demonstrated that they have strong associative learning abilities, as well as social learning skills. Interestingingly, their strong visual acuity allows them to distinguish between specific humans.  Goldfish are “friendly” towards each other and they rarely harm each other, even during breeding, although they do compete with each other for food.

Breeding usually happens after a significant change in temperature, often in spring. Goldfish lay adhesive eggs that attach to aquatic plants and the eggs hatch within 48 to 72 hours. Dense plants such as Cabomba or Elodea or a spawning mop are usually used to catch the eggs. The eggs should be separated into another tank before the parents eat them. The fry grows fast and begins to look more like a goldfish in shape with metallic brown body colour after about a week but full body colour may take as long as a year to develop.

There are fancy varieties of Goldfish which include Black Moor, Bubble eye, Butterfly tail, Calico, Celestial eye, Fantail, Lionchu, Lionhead, Oranda, Panda Moor, Pearlscale, Pompom, Ranchu, Ryukin, Telescope eye, and Veiltail.