Goldfish remember for months and see four primary colours
Carassius auratus began as Chinese carp mutations more than a thousand years ago and became one of the world's favourite aquarium fish. Selective breeding under Song and Ming courts locked in colours and fancy fins. They are tetrachromats with ultraviolet vision, and their memory spans at least three months.
Jin-dynasty records already noted red, orange, or yellow carp sports among grey food fish. Tang gardeners kept them in ornamental ponds; Song breeders, by eleven sixty-two, reserved imperial yellow for the court. Ming indoor rearing let fragile mutations survive, including fancy tails. Fish reached Japan in sixteen oh three, Portugal in sixteen eleven, and North America around eighteen fifty. Genetics now ties modern goldfish to southern Chinese C. auratus, not crucian or Prussian carp.
Wild adults often run twelve to twenty-two centimetres and can hit forty-one. Pet growth tracks tank size without the myth that fish stop at bowl dimensions. Record catches include a forty-eight-centimetre Dutch fish cited by the BBC in two thousand eight and a four-point-one-kilogram fifteen-inch fish from a South Carolina lake in twenty twenty. Four cone types sense red, green, blue, and ultraviolet; hearing uses otoliths plus Weberian ossicles linking the swim bladder. They endure brief total anoxia via liver glycogen and a vertebrate-unique pyruvate decarboxylase—likely a winter ice adaptation—and tolerate brackish water to salinity seventeen.
Schooling generalists rarely harm tankmates except by outcompeting fancy slow swimmers for food. They learn socially and as individuals, tell people apart, and beg when familiar owners approach. Positive reinforcement trains colour-light cues and tricks; China now lists about three hundred breeds, from hardy commons and Shubunkins to dragon-eye and eggless-dorsal forms that may need hand stripping to spawn. Adhesive eggs hatch in forty-eight to seventy-two hours; fry stay metallic brown for up to a year before adult gold shows.
Source: Goldfish
