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Gambusia or mosquitofish

Gambusia or mosquitofish: restricted noxious fish
© Queensland Government
Female gambusia or mosquitofish
© Creative Commons
Female gambusia or mosquitofish illustration
© Queensland Government

Gambusia were introduced into Australia from North America as a biological control for mosquitoes, but this was unsuccessful.

Instead, they have harmed native fish by competing for resources and behaving aggressively. They nip the fins of other fish, regardless of size difference. They also prey on the eggs and larvae of native fish and frogs.

Gambusia is a restricted noxious fish under the Biosecurity Act 2014.

Description

  • Gives birth to live fish.
  • Small size, growing to less than 7cm; most only 3 or 4cm.
  • Large scales and stocky body.
  • Live and feed at, or near, the surface of the water.
  • Colour varies with habitat but usually dark grey or olive on the head and back, becoming lighter on the belly.
  • Faint pigment spots on the fins and under the eyes.

Habitat

  • Freshwater fish.
  • Commonly found in lakes, and still or slow-flowing streams.
  • Often found around the edges or among freshwater plants.
  • Inhabit warm, fresh and brackish waters at low elevations.
  • Can withstand environments not suitable for native fish, such as high temperatures and low oxygen, but they are sensitive to high salinity.

Distribution

  • Eastern Australia

Life cycle

Breeding

  • Females mature at about 18–20mm (4–6 weeks of age).
  • Can produce up to 315 young per season.
  • Produce small broods at frequent intervals, which means more offspring and more survivors.
  • Breeding season between 2–9 months.
  • Day-length may set the timing of the reproductive cycle.

Diet

  • Feeds on insect larvae, insects, plants, worms, crustaceans, snails, frog eggs and small fish.

Impacts

  • Introduced in 1929 to control mosquitoes as these fish thrive in calm, shallow, vegetated waters where mosquitoes lay their eggs.

Environmental

  • Potential to rapidly outnumber native fish and dominate aquatic communities.
  • Can survive environmental conditions that native fish find difficult.
  • Good invader traits, such as:
    • high ability to reproduce
    • flexible diet
    • tolerance of diverse environments
    • low vulnerability to predators due to burrowing.
  • Aggressive—nips the fins of other fish species, and eats their eggs.
  • Matures early, have large annual numbers of broods, and fry have a high survival rate.
  • Able to gulp air from the surface when the water is low in oxygen.

Social

  • Loss of favourite fishing locations due to invading gambusia.

Control

  • If you catch gambusia in the wild, humanely kill them and do not return them to the water. Report all invasive fish captures through our online reporting form. Take photos, if possible, to show your catch.
  • Follow the ethical euthanasia code in Euthanasia of animals used for scientific purposes (PDF, 1.8MB), the 2001 Australian & New Zealand Council for the Care of Animals in Research and Teaching publication. The most appropriate way may be to stun the fish with a sharp blow to the back of the head, just above the eyes. When done correctly, this causes brain destruction—the fish's gill covers should stop moving and eyes should remain still.
  • Intensive fishing may have the potential to reduce pest fish numbers in small enclosed waterbodies, but this practice alone is very unlikely to be effective for long-term control.

Poisoning

  • Poisons can completely remove pest fish in ponds and small dams, but are not practical for rivers and streams as these poisons also kill native fish.

Legal requirements

  • Gambusia is a restricted noxious fish under the Biosecurity Act 2014.
  • You must not keep, feed, give away, sell or release them into the environment without a permit.
  • If you catch these species, you must immediately humanely kill and dispose of them responsibly away from the waterbody.
  • By law, you have a general biosecurity obligation (GBO) to take reasonable and practical steps to minimise the risks associated with restricted noxious fish under your control.

Further information

Contact

General enquiries 13 25 23