Goldfish

Goldfish (Carassius auratus) are freshwater fish in the carp family, Cyprinidae. They are among the most popular aquarium fish, and they are also well liked as pond fish because they are small, inexpensive, colourful and very hardy.

Breeds vary greatly in size, body shape, fin arrangement and colour. Combinations of white, yellow, orange, red, brown and black are known. Wild Goldfish typically reach 12 to 22 cm, and a few grow much larger. Pet Goldfish size depends on the breed and the water they live in.

Goldfish have no stomach, are classed as coldwater fish, and can live in unheated tanks at a temperature comfortable for people.

Goldfish are native to China. They descend from carp that had been reared as food fish in East Asia for thousands of years. Gold colour mutations in these normally grey or silver fish were first recorded during the Jin dynasty (266-420).

During the Tang dynasty, people raised carp in ornamental ponds, and a natural mutation produced yellowish-orange fish that were then selectively bred. By the Song dynasty, breeding was firmly established. Yellow was the imperial colour, so people outside the imperial family were forbidden to keep the yellow variety. Under the Ming dynasty Goldfish began to be raised indoors, and the first fancy-tailed Goldfish were recorded.

Goldfish reached Japan in 1603 and Portugal in 1611, and spread from there across Europe. In southern Europe in the 1620s they symbolised good luck and fortune. They arrived in North America around 1850. Today about 300 breeds are recognised in China.

Goldfish are gregarious and show schooling behaviour. They are described as friendly towards one another, and it is very rare for one to harm another. The main threat they pose to each other is competition for food, since fast breeds such as commons and comets can eat everything before slower fancy varieties reach it.

They learn well, both individually and from each other. They can tell individual people apart, and may swim to the front of the glass or the surface when their owner approaches while hiding from strangers. They often seem to beg for food.

Goldfish remember things for at least three months, can tell apart shapes, colours and sounds, and can anticipate feeding times. With positive reinforcement they can be trained to respond to coloured lights or perform tricks. They see four primary colours, including ultraviolet.

In a pond in winter they become sluggish, stop eating and often stay on the bottom, becoming active again in spring.

Goldfish can live beyond 10 years in captivity. The idea that they die quickly is often due to poor conditions rather than their nature.

They produce a lot of waste, and a build-up of it in the water can reach toxic levels and kill them. Fishbowls and very small tanks are linked with death, disease and stunting because of low oxygen and high ammonia and nitrite levels.

Rapid temperature changes can kill Goldfish, especially in small tanks. Temperatures under about 10 °C are dangerous to fancy varieties, and temperatures over 30 °C can also harm them. Their best range is 20 to 22 °C.

Overfeeding can block the intestines, most often in selectively bred Goldfish with a convoluted gut. Touching them can damage the protective slime coat, exposing the skin to bacteria and parasites. Some extreme fancy forms are much less hardy than types closer to the original fish.

This is general awareness only, not veterinary advice. Always consult a vet about your pet's health.

What is a goldfish?

It is a small freshwater fish in the carp family, native to China. Many colours and body shapes have been bred over centuries.

How long do goldfish live?

In captivity they can live for more than 10 years. Early deaths are often put down to poor conditions.

Do goldfish grow to fit their tank?

No, that is a myth. Tank size does influence growth rate, but breed matters too. All varieties can reach about 5 inches, and single-tailed breeds such as commons and comets often exceed 1 foot.

Are goldfish happy in a bowl?

No. Bowls are harmful to Goldfish because of low oxygen and high ammonia and nitrite levels. The bowl habit came from a misunderstanding of Chinese display vessels, which were only used temporarily.

Can you stroke a goldfish?

They do not like being petted. Touching can damage their slime coat and expose the skin to infection, although they can be trained to take food from fingers.

Can goldfish live in a pond all year?

Some types can in temperate climates, including commons, comets, shubunkins and some hardier fantails. Moors, veiltails, orandas and lionheads can only stay out in summer in cooler places.

Goldfish gradually turn almost grey if left in the dark, because they make pigment in response to light, much as human skin tans.

Fast-growing fry start out metallic brown like their wild ancestors, and it can take a year to gain adult colour.

Goldfish can survive short periods with no oxygen at all, which is thought to be an adaptation to frozen water in winter.

In 1620s southern Europe, husbands gave their wives a goldfish on their first anniversary as a symbol of prosperous years ahead.

A Goldfish called Goldie from Folkestone measured 15 inches in 2008, and a 2010 pond catch in Poole measured 16 inches and weighed 5 pounds.

In Iran, Goldfish are a traditional part of Nowruz celebrations.