Goldfish

• It has given rise to dozens of ornamental varieties of extremely varied shape and colour.
• It eats zooplankton, insect larvae and plant matter.
• It is considered invasive in many regions where it has been introduced.
• It was the first fish domesticated as a companion animal: the selective breeding of colour varieties began in China during the Song dynasty, more than a thousand years ago.
• Released into the wild it does not stay small or orange. It reverts to the wild brown colour and can exceed 40 cm and several kilos, and it is listed as invasive in numerous countries.
• It survives for weeks without oxygen by converting lactic acid into ethanol and expelling it through its gills, a metabolic pathway exceptional among vertebrates that allows it to overwinter beneath the ice in enclosed ponds.
• Its reputation for a three-second memory is false: conditioning experiments show that it retains what it learns for months.
• By stirring up the bottom to feed it clouds the water and uproots submerged vegetation, degrading the ecosystems into which it is introduced.

Skeleton type

Vertebrate - bony skeleton (fish)

Habitat & environment

Slow-flowing vegetated fresh water of China and East Asia; widely introduced worldwide

Birth weight

Egg 1.2-1.5 mm long; 4.5 mm long on hatching

Size at birth

4.5 mm long at hatching

Sexual maturity

1-2 years

Gestation / incubation

48-72 hours of egg development at 20-23°C

Litter / clutch size

Thousands of eggs per clutch, repeated several times through the breeding season

Sources consulted: USGS NAS Species Profile; Animal Diversity Web; A-Z Animals; FishBase; Shrimp and Snail Breeder; De Peces (guía); Academia.edu (reproductive periodicity study)