Fish

Mosquitofish

Gambusia · also called mosquitofish, plague minnow, gambusia

Least Concern → carnivoreomnivore Rivers & wetlands Coasts & shorelines

A mosquitofish is a small grey livebearer with an outsized history. For a century it was shipped around the world and dumped into ponds and paddies to fight malaria, on the strength of its appetite for mosquito larvae. It turned out to be no better at the job than the local wildlife it displaced — and, in country after country, a serious threat to native fish and frogs. Australians call it the plague minnow.

Overview

Mosquitofish are two North American species in the genus Gambusia, small livebearers related to guppies and mollies, with females reaching ~6 cm and males half that. They are aggressive surface feeders — mosquito larvae, zooplankton, and, crucially, the eggs, larvae, and fins of other animals.

Spread with good intentions

From the early 1900s, mosquitofish were exported from the US to dozens of countries for mosquito control and are now on every continent but Antarctica. But research consistently shows they are no better than native predators already present, and that by eating those predators they can make mosquito problems worse.

An invasive disaster

Mosquitofish tolerate water too hot, salty, foul, or oxygen-poor for most fish and breed explosively, so they dominate degraded waters fast. They nip the fins and eyes of larger fish, tadpoles, and newts, and kill juvenile native fish by harassment. They are on the IUCN’s 100 worst invasive species list and are a declared noxious species in Australia. Ironically, several of their Gambusia relatives — spring specialists in Texas and Mexico — are Endangered or extinct.

Status

Least Concern — abundant in its native range and everywhere it has been introduced. The concern is the damage it does, not any risk to the species.

Mosquitofish: common questions

Do mosquitofish actually control mosquitoes?

They eat mosquito larvae, but the evidence that stocking them reduces mosquito-borne disease or even mosquito numbers is weak. In most situations the native fish, dragonfly larvae, backswimmers, and other predators already present control mosquitoes just as well, and adding mosquitofish often reduces those native predators through competition and predation, which can leave more mosquitoes, not fewer. Public health agencies increasingly recommend eliminating standing water, using native fish, or using targeted larvicides instead. Mosquitofish still get stocked in some places, largely through inertia.

Why are mosquitofish such a problem as an invasive species?

Because they combine extreme hardiness, fast breeding, and aggression. They survive foul, warm, low-oxygen water that excludes competitors, a single female can found a population and produce dozens of live young repeatedly through a summer, and they attack far more than mosquito larvae, nipping the fins and eyes of larger fish, eating fish and amphibian eggs and larvae, and killing juvenile native fish by harassment. Introduced worldwide with good intentions, they have contributed to the decline of native fish and frogs on several continents and are on the IUCN list of the hundred worst invasive species.

What is the difference between a mosquitofish and a guppy?

They are close relatives, both small livebearers in the same family, and wild-type guppies and mosquitofish look alike, being small, plain, olive-silver fish. The differences are that guppies come from northern South America and the Caribbean and mosquitofish from North America, guppy males are usually colourful while mosquitofish are drab in both sexes, and mosquitofish are more cold-tolerant and considerably more aggressive. In the aquarium trade the guppy is a hugely popular pet, while the mosquitofish is rarely kept and is illegal to release or, in places like Australia, even to possess.

Can I keep mosquitofish in a pond or aquarium?

In their native range in the United States, mosquitofish are sometimes kept in garden ponds, and some mosquito-control districts give them away, but in many other countries, including Australia and New Zealand and parts of Europe, they are a prohibited noxious species that must not be kept, moved, or released. Even where legal, they are poor community aquarium fish because they nip fins and harass tankmates, and putting them in a pond that could overflow or connect to a waterway risks releasing an invasive species. A native livebearer or a guppy is a better choice.

Sources & further reading

Written by HideShark Editorial Team · reviewed by HideShark Science Desk. Published September 11, 2026. Last updated September 11, 2026.

Quick facts

Scientific name: Gambusia
Diet: An aggressive surface feeder taking mosquito larvae and pupae, other insect larvae, zooplankton, small crustaceans, and some algae and detritus, and it also readily eats the eggs, larvae, and fins of other fish and amphibians, which is the root of its impact as an invader
Two American species: The two mosquitofish, the western and eastern mosquitofish of the southern and central United States and northeastern Mexico, are small livebearers in the genus Gambusia, related to guppies, mollies, and swordtails, with females reaching about 6 cm and males only 3 to 4 cm
Spread for malaria control: From the early 20th century, mosquitofish were shipped from the United States to dozens of countries and released into ponds, rice paddies, wells, and ditches to control the mosquitoes that spread malaria and other diseases, and they are now established on every continent except Antarctica
No better than the natives: Studies repeatedly find that mosquitofish are no better at controlling mosquitoes than the native fish and invertebrate predators already present, and that they often make things worse by eating those native predators, yet they continue to be stocked in some places out of habit
The plague minnow: In Australia, where it is called the plague minnow or gambusia, the mosquitofish has spread through most of the continent's fresh waters and is blamed for declines in native rainbowfish, pygmy perch, and several frogs through fin-nipping, egg predation, and competition, and it is a declared noxious species
Tolerant of almost anything: Mosquitofish survive in water too warm, too salty, too low in oxygen, or too polluted for most fish, tolerate temperatures from near freezing to around 40 degrees Celsius, and breed rapidly, a female producing several broods of live young a summer, which lets them colonise and dominate degraded waters fast
Fin-nippers: Mosquitofish attack the fins and eyes of larger fish and of tadpoles and newts, and they will kill juvenile native fish many times their size by repeated nipping, behaviour that makes them destructive out of proportion to their size
Range: Native to the fresh and brackish waters of the southern and central United States and northeastern Mexico, in ponds, ditches, marshes, slow streams, and lake margins, and introduced and established across every warm and temperate region of the world, from southern Europe and Africa to Australia, New Zealand, and much of Asia, in a wide range of still and slow waters including degraded and polluted ones.
Conservation status: Least Concern → ≈ The two widespread mosquitofish are common in their native range and abundant almost everywhere they have been introduced, and are assessed as Least Concern. The conservation issue with mosquitofish is the harm they do as invaders, in that they are listed among the world's worst invasive species and are implicated in the decline or local extinction of native fish, frogs, newts, and invertebrates across North America, Australia, southern Europe, Africa, and Asia. Several other members of the genus Gambusia, by contrast, are highly threatened, including spring-dwelling species in Texas and Mexico that are Endangered or already extinct through groundwater loss and, in some cases, hybridisation with the introduced mosquitofish in the wild