FishfreshwaterUndemanding

Eastern mosquitofish

A small livebearer distributed worldwide for mosquito control, which it performs no better than native fish, and which has caused documented harm to native species everywhere it has established. It is included here to be recognised and, in most places, not kept.

Quick profile

Scientific name: Gambusia holbrooki
Adult size: 3.5–6 cm (1.4–2.4 in)
Lifespan: 1–3 years
Temperature: 4–35 °C (39–95 °F)
pH: 6.5–9
Hardness: 5–30 °dGH
Minimum tank: 40 L (11 US gal)
Minimum length: 55 cm
Swimming zone: Upper level
Social: Loose group — at least 4
Diet: Omnivore
Overall confidence: moderate confidence

What keeping this species involves

It survives conditions that kill almost everything else, which is the reason not to keep it rather than a reason to.

Almost any still or slow fresh or brackish water, including drains, ponds and ditches, tolerating extremes of temperature, salinity and oxygen.

Identity and names

Common name: Eastern mosquitofish
Scientific name: Gambusia holbrooki
Family: Poeciliidae
Order: Cyprinodontiformes
Class: Actinopterygii
Also sold as: Gambusia holbrooki, mosquitofish, gambusia, plague minnow

Adult size and growth

3.5–6 cm (1.4–2.4 in)

Typical lifespan in an aquarium: 1–3 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.

Shape, which is what the compatibility engine reads instead of length alone: fusiform — the ordinary torpedo with a small terminal mouth. Assigned from what is typical of Poeciliidae, not examined for this species.

Water and tank requirements

Recorded for completeness. This is a species AquariumHQ does not recommend keeping, and in many jurisdictions the question does not arise because it is prohibited.

Temperature (°C)

Eastern mosquitofish

4–35

Scale: 0 to 36 °C.

pH (pH)

Eastern mosquitofish

6.5–9

Scale: 4 to 9.5 pH.

Hardness (°dGH)

Eastern mosquitofish

5–30

Scale: 0 to 30 °dGH.

The bands AquariumHQ publishes for the eastern mosquitofish, each drawn against the full range this catalogue uses for that parameter. A narrow band on a wide scale is a specialist; a wide one is a genuinely tolerant animal. Source: AquariumHQ husbandry position for this record — an editorial range, not a measurement

Why these ranges: One of the widest tolerances recorded for any freshwater fish, spanning near-freezing to well over thirty degrees Celsius and fresh to substantially brackish water. The figures document why it establishes so readily and are not a husbandry recommendation.

Where these figures come from

Habitat class

Temperate still water

Ponds, lakes, canals and slow rivers outside the tropics, with a genuine winter.

The temperature range is the point. These animals experience a seasonal cycle, and keeping them at a constant tropical temperature shortens their lives without ever looking like the cause.

Conductivity: 150–800 µS/cm
Flow: still
Dissolved oxygen: variable
Seasonality: strong

These are figures for the KIND of water body, not measurements of this species. They are AquariumHQ’s summary of the general limnology and are given wide because the water is.

TemperatureReasoned on this record: This record states its own reason for this band. See the water section.
pHReasoned on this record: This record states its own reason for this band. See the water section.
General hardnessReasoned on this record: This record states its own reason for this band. See the water section.

Requirement	Value	Notes
Temperature	4–35 °C (39–95 °F)	Stability matters more than hitting an exact figure.
pH	6.5–9	A stable pH outside the ideal band is usually better than an unstable one inside it.
General hardness	5–30 °dGH	Check your supplier's published figure before choosing species.
Minimum volume	40 L (11 US gal)	A floor, not a recommendation.
Minimum footprint	55 cm long × 25 cm deep	Recorded for completeness. This is a species AquariumHQ does not recommend keeping, and in many jurisdictions the question does not arise because it is prohibited.
Water flow	low	Match the outflow to this rather than to the filter's rating.
Lid required	Recommended	Reduces evaporation and prevents accidents.
Structure	Dense planting, which is the only protection fry and tankmates have from the adults.

Behaviour

Attacks the fins and eyes of larger fish persistently, which is documented as a mechanism of displacement rather than an aquarium curiosity.
Matures within weeks and produces broods repeatedly through a long season, which is why introduced populations expand so fast.

Telling males from females

Females are considerably larger with a dark gravid spot; males are small with a gonopodium and sometimes with black mottling.

Feeding

Eats zooplankton, insect larvae, algae, and the eggs, fry and fins of other fish. The last of these is the documented mechanism behind much of its ecological impact.

Diet type: Omnivore
Staples: Quality flake, Frozen daphnia, Frozen bloodworm

Breeding

Strategy: Livebearing, with large frequent broods and very early maturity
Difficulty: incidental
Parental care: bearer

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	high	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	none	Applies to snails you wanted as well as snails you did not.
Long or trailing fins	frequent	Fin damage is an entry point for secondary infection.
Plants	none	Tough species such as Anubias and Java fern survive most grazers.

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.

Widely introduced for mosquito control on evidence that does not support it; several reviews find native fish equally or more effective and the introduction harmful.
Listed among the world's most damaging invasive species. It should never be released, and in many jurisdictions it should not be acquired at all.

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 the Atlantic and Gulf coastal plains of the United States; introduced across every continent except Antarctica
Habitat: Almost any still or slow fresh or brackish water, including drains, ponds and ditches, tolerating extremes of temperature, salinity and oxygen.

What the checklists say

111 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	94	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	17	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

Declared a noxious or prohibited species across much of Australia and restricted in a number of other jurisdictions. In parts of its introduced range it is instead actively distributed by public health bodies, so the legal position is genuinely contradictory between countries and must be checked locally rather than assumed.

Where this species has been introduced, and what followed

Europe — recorded in 33 countries, first in Spain in 1921

Established

Biological control, recorded twice — once unflagged and once with HIGH uncertainty. Gambusia holbrooki was distributed across southern Europe from 1921 by public health authorities to control malarial mosquitoes, and the aquarium trade had nothing to do with it. It is now listed as of Union concern.

Deliberate stockingSomebody put the species into open water on purpose, for food, angling, ornament or mosquito control — frequently a government agency, and frequently before anyone considered the consequences.
Escape from food or bait aquacultureFood and bait production, at a scale no private keeper approaches. The animals are held in numbers, in ponds, often on floodplains.

What has been established

Predation on native speciesMeasured in studyRated HIGH against nature protection and restoration. Gambusia takes the eggs and larvae of native fish and amphibians, and in the Mediterranean it is implicated in the decline of several endemic cyprinodontids that occupy the same shallow warm water.
Carries parasites or pathogensReported in the literatureRated HIGH against animal health, on the parasites and pathogens carried alongside a fish distributed deliberately and repeatedly across a continent by public health programmes.
Competition with native speciesMeasured in studyWhether it even controls mosquitoes better than the native fish it displaced is contested in the literature, which makes this the clearest case in the batch of a deliberate introduction whose stated purpose was not clearly achieved.

Of Union concern. Sold occasionally as a hardy livebearer and prohibited across the EU; the closely similar Gambusia affinis is a different species with a different legal status in some jurisdictions, and they are not reliably separable by eye.

EASIN — European Alien Species Information Network · EASIN catalogue record R06574 (apixg/catxg) · read 2026-08-30. A European network: the routes and effects recorded here are the ones documented in Europe. EASIN compiles national inventories, DAISIE and CABI rather than measuring, and its pathway assignments carry its own uncertainty flags, which are reported above where it sets them.

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.

EU

Prohibitedpossession

Gambusia holbrooki Girard, 1859 appears by name in the Union list, added by the 2022 amendment, alongside its western congener Gambusia affinis. Article 7 prohibits keeping, breeding, transporting, placing on the market, using, exchanging and releasing either.

Instrument: Regulation (EU) No 1143/2014, Article 7, as applied to the Union list in Commission Implementing Regulation (EU) 2016/1141 (consolidated text 02016R1141-20220802)

Both Gambusia species are listed, which matters because the two are difficult to distinguish and are used interchangeably in mosquito-control programmes. A keeper cannot escape the listing by arguing about which species they have.

Checked against the instrument · last checked 2026-08-29 · An editor has read the current text of the named instrument and confirmed this species' entry on the date shown.

AU

Prohibitedpossession

The species is declared noxious across much of Australia, where possession and movement of live fish are offences under state law. The specific declarations differ between states and territories and have not been read individually here.

Instrument: State and territory noxious-fish declarations made under fisheries and biosecurity legislation

The legal position on this species is genuinely contradictory between countries. In parts of its introduced range public health bodies still distribute it deliberately for mosquito control, while in Australia and the EU possession is an offence. Neither position can be inferred from the other.

Instrument recorded, species entry not re-checked · last checked 2026-08-29 · 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.

JP

Permit requiredpossession

Both Gambusia affinis and G. holbrooki are designated by name. A keeping permit under the Act may be granted for academic research, exhibition, education and similar purposes. The Ministry states directly that keeping as a pet is not among them, so for an aquarist the practical effect of “permit required” is prohibition.

Instrument: Act on the Prevention of Adverse Ecological Effects Caused by Designated Invasive Alien Species (Act No. 78 of 2004), as amended 2022 — designated invasive alien species, Gambusia holbrooki

Checked against the instrument · last checked 2026-08-30 · An editor has read the current text of the named instrument and confirmed this species' entry on the date shown.

JP

Prohibitedrelease

Release is prohibited. Gambusia were introduced to Japan and to much of the rest of the world deliberately, as a mosquito-control measure, which is the historical reason the genus is now on prohibition lists across four continents.

Checked against the instrument · last checked 2026-08-30 · An editor has read the current text of the named instrument and confirmed this species' entry on the date shown.

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	Gambusia holbrooki	Observed / measured	high confidence	Catalogue of Life; GBIF — Global Biodiversity Information Facility
native range	Native to the Atlantic and Gulf coastal plains of the United States; introduced across every continent except Antarctica	Observed / measured	moderate confidence	GBIF — Global Biodiversity Information Facility
adult size	3.5–6 cm	Aquarium-literature consensus	moderate confidence	AquariumHQ husbandry synthesis
lifespan	1–3 years	Aquarium-literature consensus	moderate confidence	AquariumHQ husbandry synthesis
temperature	4–35 °C	Aquarium-literature consensus	moderate confidence	AquariumHQ husbandry synthesis
ph	6.5–9 pH	Aquarium-literature consensus	moderate confidence	AquariumHQ husbandry synthesis
general hardness	5–30 °dGH	Aquarium-literature consensus	moderate confidence	AquariumHQ husbandry synthesis
minimum tank volume	≥ 40 L	AquariumHQ editorial position	moderate confidence	AquariumHQ husbandry synthesis
minimum tank length	≥ 55 cm	AquariumHQ editorial position	moderate confidence	AquariumHQ husbandry synthesis
minimum group size	≥ 4	AquariumHQ editorial position	moderate 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 2026-08-29. 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. 111 distribution statements held from GBIF checklists — introduced in 93 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 sourceAquariumHQ's own position, derived from evidenced inputs.1 citation, 1 independent origin

A single source: usgs-nas.

6.5 cm — USGS Nonindigenous Aquatic Species database · Maximum recorded · Observed in the wild · checked 2026-08-29

What this kind of claim needs: size a well-kept specimen reaches — no external source is required, provided AquariumHQ shows its reasoning. A documented maximum is held and the catalogue's typical adult range is stated separately, with the relationship between them recorded rather than collapsed. The largest recorded specimen exceeds the typical adult size by a normal margin. Most individuals will not approach it, and it is not a planning figure.

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.

temperatureAquariumHQ'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.

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.

Guides relevant to this species

Chosen from this record's own traits rather than listed on every page.

Schooling and shoalingThis species is recorded as loose group, and the number it is kept in decides how it behaves.
Predator and prey sizeIt takes fish that fit in its mouth, and its mouth grows with it.
Native, introduced and invasiveThis record carries an invasive or legal note, and those are five separate claims that are easy to read as one.
Wild conditions and aquarium recommendationsThe water band on this page is an AquariumHQ position with a stated reason, not a measurement of a river.
Why fish size figures disagreeA documented maximum and a typical adult size are both held for this species, and they are different quantities.
How aquarium species get into the wildThis species has a documented introduction outside its native range, with the route recorded.
What a legal restriction on a species actually meansAquariumHQ holds a structured legal status for this species, and possession, sale, import and release are four separate questions.
How to read a compatibility verdictThis animal is recorded as nipping fins, which is one of the few compatibility factors with real reports behind it.

Eastern mosquitofish

Quick profile

What keeping this species involves

Identity and names

Adult size and growth

Water and tank requirements

Where these figures come from

Group size and social behaviour

Behaviour

Telling males from females

Feeding

Breeding

Tankmates and compatibility

Welfare considerations

Problems to watch for

Where it comes from

What the checklists say

Legal status and responsible practice

Where this species has been introduced, and what followed

Europe — recorded in 33 countries, first in Spain in 1921

What has been established

EU

AU

JP

JP

Evidence

Why we say this

Guides relevant to this species