Gambusia holbrooki (Gambusia) was introduced to Sydney in 1925. Gambusia are native to the Gulf of Mexico drainage and were introduced to Australia via Italy. Gambusia are sometimes incorrectly referred to as mosquito fish.

Queensland

They were accidentally introduced to Brisbane in 1929 and were subsequently spread by the military and local councils as a biological control agent for mosquitoes and the tropical disease malaria. They were introduced to Cairns in 1943.

Distribution in Queensland

Gambusia are:

widespread throughout Queensland (and mainland Australia) and extremely abundant in some areas
well-established in 90% of urban creeks in Brisbane and are the most widely distributed exotic species

Potential for spread

Gambusia are already widespread. There may be some potential for spread into remaining pristine (undamaged) environments in inland Australia and other isolated freshwater bodies.

Biology

Reproduction

Gambusia give birth to live young.
Female gambusia mature between 18 and 20 mm (i.e. 4-6 weeks of age). They average 30-50 young per brood (up to nine broods a year); with larger broods produced early in the season. The breeding season varies between 2 and 9 months.
Photoperiod (day length) is believed to determine the timing of the reproductive cycle; in Brisbane breeding begins in August (when daylight is more than 11 hrs).

Environmental tolerances

Gambusia can withstand conditions that native fishes cannot, such as high temperatures and low dissolved oxygen. However, they are sensitive to high salinity. They are able to gulp air from the surface when there is not enough oxygen in the water.

Habitat preferences

Gambusia prefer shallow regions of freshwater creeks, but are found in a variety of habitats in Australia.

They are found both in disturbed and undisturbed water bodies.

Movement

Local movement but no specific migration.

Feeding habits

Gambusia select for small prey (invertebrates), and have high levels of diversity and variability in their diet. There is only limited evidence of preying on other fish.

Effect on environment

Current

Gambusia:

are avoided by both native and exotic fish predators when given a choice of prey
have been reported to have a light parasite burden in Australia, while native species have a higher parasite load
are aggressive and nip the fins of native fishes. This can lead to infection and death. In many places in Queensland where gambusia are found, few or no native species are present.
have a significant impact on other species, including important sportfish through predation (fin-nipping, eating eggs and fry), as well as through competition for habitat and food resources. Native species have been reported to decrease in abundance where G. holbrooki is present.
have been implicated in the decline of species of Ambassis, Chlamydogobius, Craterocephalus, Galaxias, Melanotaenia, Mogurnda, Pseudomugil, Retropinna and Scaturiginichthy, as well as other native species in Australia including those responsible for mosquito control.

Potential for spread

The potential impact of gambusia is greatest in sensitive areas (pristine environments) that support rare and/or endemic species of small native fishes, such as mound springs. There are also potential impacts from introduced diseases/parasites.

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Student resource i.2 Introductory

Priority species: Gambusia (Gambusia holbrooki)

History of introduction

Australia

Queensland

Distribution in Queensland

Potential for spread

Biology

Reproduction

Environmental tolerances

Habitat preferences

Movement

Feeding habits

Effect on environment

Current

Potential for spread

Student resource i.2
Introductory