FishfreshwaterModerateHigh invasive risk

Goldfish

A large, long-lived, cold-water pond fish that has spent a century being sold as a bowl ornament. Single-tail goldfish reach 25–30 cm, live for decades, produce an enormous waste load and cannot be kept properly in an indoor tank of ordinary size.

Quick profile

Scientific name: Carassius auratus
Adult size: 20–35 cm (7.9–13.8 in)
Lifespan: 10–25 years
Temperature: 10–22 °C (50–72 °F)
pH: 7–8.5
Hardness: 8–25 °dGH
Minimum tank: 400 L (106 US gal)
Minimum length: 150 cm
Swimming zone: All levels
Social: Loose group — at least 2
Diet: Omnivore
Overall confidence: high confidence

What keeping this species involves

Hardy, but the waste output, adult size, lifespan and cold-water requirement together are far beyond what a typical indoor tank supports.

Cool, slow, vegetated fresh water — ponds, ditches and slow rivers.

Identity and names

Common name: Goldfish
Scientific name: Carassius auratus
Family: Cyprinidae
Order: Cypriniformes
Class: Actinopterygii
Also sold as: common goldfish, comet goldfish

Varieties and strains

Variety	What it means in practice
Common and comet	Single-tailed, fast, and reaching 30 cm or more. Pond fish.
Fancy (fantail, oranda, ryukin)	Twin-tailed, deep-bodied and slower. More tolerant of tank life but prone to buoyancy problems.
Bubble-eye, celestial and telescope	Selectively bred for eye deformities that impair vision and are easily damaged. AquariumHQ does not recommend them.

Adult size and growth

20–35 cm (7.9–13.8 in) — Single-tail varieties reach 25–35 cm in a pond. Fancy varieties stay shorter but grow very deep-bodied.

Typical lifespan in an aquarium: 10–25 years. Almost every animal sold in a shop is a juvenile, so the tank has to suit the size in the first line rather than the size in the bag.

Water and tank requirements

A 30 cm fish with a very high waste output, kept in a group. A pond is the honest answer for single-tail varieties; a large tank is the minimum for fancy ones.

Requirement	Value	Notes
Temperature	10–22 °C (50–72 °F)	Stability matters more than hitting an exact figure.
pH	7–8.5	A stable pH outside the ideal band is usually better than an unstable one inside it.
General hardness	8–25 °dGH	Check your supplier's published figure before choosing species.
Minimum volume	400 L (106 US gal)	A floor, not a recommendation.
Minimum footprint	150 cm long	A 30 cm fish with a very high waste output, kept in a group. A pond is the honest answer for single-tail varieties; a large tank is the minimum for fancy ones.
Water flow	low	Match the outflow to this rather than to the filter's rating.
Lid required	Recommended	Reduces evaporation and prevents accidents.

Behaviour

Digs continually through substrate and uproots most planting.
Eats soft aquatic plants readily.

Feeding

Floating flake makes fancy goldfish gulp air, which contributes to the buoyancy problems so often described as 'swim bladder disease'. Feed sinking food.

Diet type: Omnivore
Staples: Sinking goldfish pellets, Blanched vegetables, Frozen daphnia and bloodworm, Aquatic plants

Breeding

Strategy: Egg-scattering over plants in spring
Difficulty: straightforward
Parental care: none

Tankmates and compatibility

Assessments are derived from stored traits by the compatibility engine, with the reasoning shown. A verdict is a statement about probability, not a guarantee — individual temperament can override it.

Risk this species poses to common tankmates
Towards	Risk	What it means
Small fish	moderate	Anything that fits in the mouth is at risk once this species reaches adult size.
Adult dwarf shrimp	high	Cover reduces losses but rarely prevents them where the risk is high.
Shrimplets	near-certain	Determines whether a shrimp colony can grow rather than merely persist.
Snails	moderate	Applies to snails you wanted as well as snails you did not.
Long or trailing fins	none	Fin damage is an entry point for secondary infection.
Plants	consumes	Tough species such as Anubias and Java fern survive most grazers.

Assessed pairings

Any pair in the catalogue can be assessed with the compatibility checker.

Welfare considerations

Points where the way this species is commonly sold or kept differs from what it actually needs.

Bowls are unsuitable, and so are most tanks under about 200 L.
Cannot be kept with tropical fish: the temperature ranges do not overlap usefully and goldfish are far too messy for a planted community.
Established as an invasive species across the world, largely through releases into ponds and waterways. Never release.

Problems to watch for

Most problems in a tank containing this species are general rather than species-specific. Start with the troubleshooting index and work from the observation rather than from a guess at the cause.

What AquariumHQ does not yet hold

Species-level disease susceptibility is modelled in the graph and is not yet populated. Health pages will not be published until each condition has veterinary sourcing, because health content written without evidence is the most harmful thing this product could publish. The gap is recorded in the coverage report.

Where it comes from

Native range: Native to East Asia; domesticated in China over a thousand years ago and introduced worldwide
Habitat: Cool, slow, vegetated fresh water — ponds, ditches and slow rivers.

What the checklists say

106 distribution statements retrieved from GBIF checklists. Establishment means is reproduced from the source where it states one, and left unstated where it does not — a record of presence is not a record of origin.

Status	Places	What this means
Introduced	87	A checklist states the species arrived here with human help. That is not a statement that it is established, harmful or illegal.
Recorded as present, establishment means not stated	19	The source records the species as present and does not say whether it is native or introduced. AquariumHQ does not fill that in.

No checklist AquariumHQ holds positively calls this species native anywhere, so the native range above rests on AquariumHQ’s own reading of the literature rather than on a cited checklist.

Legal status and responsible practice

Restriction note

Established feral populations exist on every inhabited continent and are implicated in the decline of native species. Release is prohibited in many jurisdictions and is never acceptable.

What AquariumHQ has recorded, by jurisdiction, with the instrument each entry comes from and how far the check went. Ecological risk and legal status are separate: a species can be ecologically risky and legally unrestricted, or restricted where it could never establish.

GB

Prohibitedrelease

Goldfish are not native to Great Britain, so releasing one — into a river, a canal, a drain or an unmanaged garden pond connected to open water — is an offence. This catches the single commonest way an unwanted goldfish is disposed of.

Instrument: Wildlife and Countryside Act 1981, section 14

Instrument recorded, species entry not re-checked · last checked 2026-08-11 · AquariumHQ has recorded the instrument and what it does, but has not re-confirmed this species' entry against the current consolidated text. Listings are amended, so treat this as a pointer to the right law rather than as a confirmation of the current position, and check with the authority before acting.

AU

Prohibitedrelease

Goldfish are established in Australian waterways and are treated as a pest species in several states, with corresponding restrictions on release and in some cases on transport of live fish.

Instrument: State and territory noxious-fish and biosecurity legislation, which varies between jurisdictions

Australian fisheries rules are state and territory matters and differ substantially. Check the rules for your own state rather than relying on a national statement.

US

Prohibitedrelease

Goldfish have established feral populations across much of the United States, where they grow far larger than aquarium specimens and contribute to turbidity and habitat degradation. Release is restricted by state law.

Instrument: State fish and wildlife regulations; goldfish are documented as established non-native populations in the USGS Nonindigenous Aquatic Species database

Never release aquarium life into the wild

Aquarium animals, plants, and aquarium water must never be released into ponds, rivers, canals, drains or the sea — not even in a country where the species is sold freely. Released fish and invertebrates establish populations that displace native species, and released plants and water carry pathogens, parasites and fragments capable of spreading without any animal at all. If you can no longer keep an animal, rehome it through an aquarium society, a retailer that accepts returns, or another keeper.

Rehome through a local aquarium society, a specialist retailer or another keeper.
Unwanted plants go in household waste or a hot compost heap, never in a watercourse or a garden pond.
Never empty a bucket of tank water into a drain that discharges to open water.
If an animal is beyond rehoming, ask an aquatic veterinarian about humane euthanasia rather than releasing it.

Legal status is recorded from the sources named and was correct on the verification date shown. Rules change, and sub-national rules often differ from national ones. Check the current position with the relevant authority before acquiring, selling or moving any animal or plant.

Evidence

Every stored value with the kind of support behind it and where to check it. Evidence type and confidence are separate axes: an editorial position held confidently and a measurement held tentatively are different things.

Claim	Value	Evidence type	Confidence	Source
scientific name	Carassius auratus	Observed / measured	high confidence	Catalogue of Life; GBIF — Global Biodiversity Information Facility
native range	Native to East Asia; domesticated in China over a thousand years ago and introduced worldwide	Observed / measured	moderate confidence	GBIF — Global Biodiversity Information Facility
adult size	20–35 cm	Aquarium-literature consensus	high confidence	AquariumHQ husbandry synthesis
lifespan	10–25 years	Aquarium-literature consensus	high confidence	AquariumHQ husbandry synthesis
temperature	10–22 °C	Aquarium-literature consensus	high confidence	AquariumHQ husbandry synthesis
ph	7–8.5 pH	Aquarium-literature consensus	high confidence	AquariumHQ husbandry synthesis
general hardness	8–25 °dGH	Aquarium-literature consensus	high confidence	AquariumHQ husbandry synthesis
minimum tank volume	≥ 400 L	AquariumHQ editorial position	moderate confidence	AquariumHQ husbandry synthesis
minimum tank length	≥ 150 cm	AquariumHQ editorial position	moderate confidence	AquariumHQ husbandry synthesis
minimum group size	≥ 2	AquariumHQ editorial position	high confidence	AquariumHQ husbandry synthesis

Last reviewed 2026-08-10. Values labelled as an aquarium-literature consensus are AquariumHQ editorial positions rather than measurements — see how evidence is handled.

Why we say this

What each figure on this page rests on, and how far that is from being independently established.

Every figure on this page has a provenance. Open any claim to see what AquariumHQ holds for it, which sources say what, and what a claim of that kind actually needs. Different claims need different evidence: an accepted scientific name is settled by one authority, while a legal restriction needs a current primary instrument. A single source is often the right answer rather than a thin one.

scientific nameAquariumHQ's own position, externally checkableBased on a verified authoritative source.

AquariumHQ's own position on a claim an external source could support.

What this kind of claim needs: accepted scientific name and classification — 1 authoritative source in an appropriate context. Checked against gbif on 2026-08-11. One authoritative backbone is what this class requires.

What would improve this: Go and read a source. This is reachable and has not been reached.

native rangeAquariumHQ's own position, externally checkableBased on a verified authoritative source.

AquariumHQ's own position on a claim an external source could support.

What this kind of claim needs: where the species occurs — 1 authoritative source in an appropriate context. 106 distribution statements held from GBIF checklists — introduced in 83 country. Establishment means is reproduced from the source, never inferred from occurrence.

What would improve this: Go and read a source. This is reachable and has not been reached.

adult sizeOne sourceBased on a verified authoritative source.1 citation, 1 independent origin

A single source: fishbase.

48–48 cm — FishBase · Maximum recorded · The range the species is recorded from · checked 2026-08-11

What this kind of claim needs: size a well-kept specimen reaches — no external source is required, provided AquariumHQ shows its reasoning. One authoritative source, which is what this kind of claim requires. Independent replication would be welcome and is not the standard.

What would improve this: Corroborate against a second, independent source.

lifespanAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.

AquariumHQ's own position on a claim an external source could support.

What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.

What would improve this: Go and read a source. This is reachable and has not been reached.

temperatureOne sourceAquariumHQ's own position, derived from evidenced inputs.1 citation, 1 independent origin

A single source: fishbase.

18–22 °C — AquariumHQ husbandry synthesis · Recommended for keeping · Recommended for keeping · checked 2026-08-11
0–41 °C — FishBase · Tolerated range · The range the species is recorded from · checked 2026-08-11Corrected on checking from 4–30 °C.
4–28 °C — GBIF — Global Biodiversity Information Facility · Observed in the wild · Observed in the wild
17–24 °C — Ornamental Aquatic Trade Association · Recommended for keeping · Recommended for keeping

What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. Derived from the observed range rather than copied from it. The observed envelope spans conditions this species meets across seasons and localities; a keeper holds one temperature continuously. The advised band trims both ends because sustained residence at an extreme is a different demand from encountering it, and stability matters more to a captive fish than breadth.

What would improve this: Corroborate against a second, independent source.

phAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.

AquariumHQ's own position on a claim an external source could support.

What would improve this: Go and read a source. This is reachable and has not been reached.

general hardnessAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.

AquariumHQ's own position on a claim an external source could support.

What would improve this: Go and read a source. This is reachable and has not been reached.

minimum tank volumeAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.

No external authority publishes this. The rationale carries the reasoning.

What this kind of claim needs: minimum tank size — no external source is required, provided AquariumHQ shows its reasoning. No authority publishes this. AquariumHQ derives it, and the derivation is recorded with its inputs and assumptions.

What would improve this: Keep the rationale current. There is no source to find.

minimum tank lengthAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.

No external authority publishes this. The rationale carries the reasoning.

What would improve this: Keep the rationale current. There is no source to find.

minimum group sizeAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.

No external authority publishes this. The rationale carries the reasoning.

What this kind of claim needs: group size — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.

What would improve this: Keep the rationale current. There is no source to find.

Goldfish

Quick profile

What keeping this species involves

Identity and names

Varieties and strains

Adult size and growth

Water and tank requirements

Group size and social behaviour

Behaviour

Feeding

Breeding

Tankmates and compatibility

Assessed pairings

Welfare considerations

Problems to watch for

Where it comes from

What the checklists say

Legal status and responsible practice

GB

AU

US

Evidence

Why we say this