Taxonomy & naming
Linnaeus described Cyprinus auratus in 1758, and the species is now placed in Carassius. The fancy goldfish of the trade and the plain wild type are the same species, though the plain-bodied fish sold to pond keepers and feeder tanks is what the atlas covers here. The Catalog of Fishes type locality reads China; Japanese rivers.
Morphology
The wild type is a deep-bodied, laterally compressed carp with no barbels, a long dorsal fin with a serrated spine, and an olive-bronze to golden body. FishBase gives a maximum of 19 in TL, though wild fish are usually far smaller. Captive strains vary widely in colour, fin shape and body form.
Habitat
FishBase gives the native range as East Asia, in China and Japan, and describes the species as introduced throughout the world with reported adverse ecological impact. It lives in slow rivers, ponds and lakes with soft bottoms and vegetation, and tolerates low oxygen and wide temperature swings.
Feeding
It is an omnivore that grubs through the substrate for insect larvae, crustaceans, plant material and detritus. In captivity it takes pellets, flakes, vegetables and live or frozen foods.
Mating
Males develop small white breeding tubercles on the gill covers and pectoral fins in spawning season and chase ripe females through vegetation.
Breeding
Goldfish scatter adhesive eggs over plants or spawning mops and give no parental care; adults will eat the eggs. Spring warming triggers spawning in ponds, and the fry are easy to raise on infusoria and fine foods.
In the aquarium
The plain wild type suits ponds and large tanks better than small bowls, because it grows large, produces much waste and needs strong filtration. FishBase lists it as highly commercial for the aquarium trade. It is a cool-water fish that does not need heating.
Conservation
The IUCN category is Least Concern, assessed in 2010. The concern is ecological: released goldfish become feral and have damaged native fish and plant communities in many regions, so they should never be dumped into open water.