What do they look like?

As there are over a hundred varieties of goldfish, coloration and physical characteristics vary greatly. The common goldfish has two sets of paired fins - the pectoral fins and pelvic fins, and three single fins- the dorsal, caudal, and anal fin. The head lacks scales. Goldfish have very large eyes and acute senses of smell and hearing. Instead of true teeth, goldfish have teeth in their throats which they use to crush food.

Where in the world do they live?

Although goldfishes originated in China, they have now spread worldwide in aquariums, ornamental pools, and into the wild.

What kind of habitat do they need?

In the wild, goldfish can be found in slow-moving, freshwater bodies of water. As with their close relative the carp, they thrive in slightly murky water. In captivity, an aquarium with live plants and a dirt bottom is ideal. Bi-weekly water changes are a good idea as a goldfish tank is hard to keep clean. Live plants must be replaced fairly regularly; goldfish enjoy eating them. Small pebbles are a suitable substitute for the pond-like bottom. Typically, goldfish will survive in water temperatures ranging from freezing to 30 degrees centegrade. Goldfish prefer a pH range of 6.5-8.5.

How do they reproduce?

Goldfish usually mature in their second year but this varies with diet, water temperature, and other environmental influences. In the wild, breeding occurs during the summer; breeding can occur year round in indoor aquariums. Mature female goldfish will become rounder during breeding; males develop small bumps on their heads, gill covers, and pectoral fins. Males chase the females for several days before spawning occurs. Females can produce several thousand eggs per spawning period up to several times every 8 to 10 days. Goldfish eggs hatch in about 4-5 days at 18-20 degrees centegrade(64-68 degrees F.).

How long do they live?

Although there is one report of a pet goldfish who lived 43 years, 25 years is a more reasonable maximum lifespan for a goldfish kept in a pond. In an aquarium, ten years is more likely. In the wild, lifespan is undoubtedly less.

How do they behave?

In the wild, goldfish often travel in schools. They are not particularly aggressive fish.

What do they eat?

In the wild, goldfish are omnivores. They eat plants, insects such as mosquito larvae, small crustaceans, zooplankton, and detritus (dead plant and animal matter found on the bottom).

In captivity, goldfish are commonly fed dried flake or pellet food. Good diet supplements include freeze dried Tubifex worms, mosquito larva, bloodworms, daphnia, brineshrimp, and vegetation such as boiled peas and lettuce.

What eats them and how do they avoid being eaten?

Just about anything that eats fish would eat goldfish.

Do they cause problems?

Introduced populations are due primarily to people releasing their pets into local waterways. Goldfish should not be released into ponds in the wild because they breed quickly and are capable of crowding out native fish species. They are considered pests in most places where they have been introduced.

How do they interact with us?

Goldfish farming has become an industry of notable size. Millions of fish are bred each year and sold to aquarium shops for resale to fish enthusiasts. In North America there is a demand for goldfish to be used as bait by anglers. Pet shops often have feeder goldfish to sell to owners of carnivorous aquarium fish.

Are they endangered?

Goldfish are quite abundant.

Some more information...

Goldfish and common carp can hybridize.

Contributors

Robin Street, University of Michigan

References

A Fishkeeper's Guide to Fancy Goldfishes; Dr. Chris Andrews; Tetra Press; 1987.

The Audubon Society Field Guide to North American Fishes, Whales and Dolphins; 1993.

Froese, R., D. Pauly, eds.. 2002. "Species summary: Carrasius auratus" (On-line). Accessed 3 April 2002 at http://www.fishbase.org.