Taxonomic name: Gambusia holbrooki (Girard 1859)
Synonyms: Gambusia affinis holbrooki
Common names: eastern gambusia (English-Australia), gambusia (English), mosquitofish (English-USA), plague minnow (English-Australia), topminnow (English-USA)
Organism type: fish
Eastern mosquito fish, Gambusia holbrooki is a small, aggressive live-bearing fish that originates from the southern United States. It has been introduced worldwide as a mosquito-control agent. G. holbrooki have been implicated in damage to native fish, amphibian and invertebrate populations.
Greenish olive to brown on the back, the sides are grey with a bluish sheen with a belly silvery-white. Females have a distinct black blotch surrounded by a golden patch occurring just above the vent. Males have a highly modified anal fin, the third, fourth and fifth rays of which are elongated and thickened to form a 'gonopodium' which is used to inseminate the female. Females are also larger than males with maximum standard lenghts of 60mm and 35mm respectively.
Craterocephalus marjoriae, Gambusia affinis, Poecilia reticulata
estuarine habitats, lakes, ruderal/disturbed, water courses, wetlands
Gambusia holbrooki prefer warm, slow flowing or still waters, and occur amongst aquatic vegetation at the edge of waterbodies in water depths of 10cm or less (Merrick and Schmida 1984; McDowall 1996; Arthington et al. 1999). Although gambusia can tolerate a broad range of environmental conditions, they tend to avoid rapid discharge, naturally variable creeks and rivers and areas of dense surface vegetation, that can obstruct access for feeding on the surface (Meffe 1984; Arthington et al. 1990; Galat and Robinson, 1992).
Gambusia holbrooki predate on amphibian eggs; and predate and compete with tadpoles, resulting in injury or death to individuals. They may have a negative influence on some frog species' choice of breeding habitat. G. holbrooki have been shown to predate upon the eggs and tadpoles of the 'Critically Endangered (CR)' yellow-spotted tree frog (see Litoria castanea in IUCN Red List of Threatened Species); the 'Endangered (EN)' green and gold frog (see Litoria raniformis in IUCN Red List of Threatened Species); and the 'Vulnerable (VU)' golden bell frog (see Litoria aurea in IUCN Red List of Threatened Species) in Australia (NSW National Parks & Wildlife Service, 2004). Gambusia spp. have been implicated in the decline in the range and abundance of native fish species worldwide (Lloyd 1990) through predation and interference competition (McKay 1984; Howe 1995; Ivanstoff and Aarn 1999; Knight 1999). The species is purported to impact on macro-invertebrates such as rotifers, mayflies, beetles, dragonflies and molluscs (Anstis, 2002).
Used as a feeder fish for aquarium species. Formerly used to control mosquitoes, but has since been shown to be generally ineffective. Since 1982 the World Health Organisation has no longer recommended the use of gambusia for malaria control purposes and indicates it should not be introduced into new areas.
Gambusia holbrooki is the only species of Gambusia in Australia. G. affinis is similar to the closely related G. holbrooki, and until relatively recently they were classed as sub-species rather than distinct species. As such, their impacts and behaviour are virtually identical, and the same management techniques will work for both species. Although hybrids between G. holbrooki and G. affinis can occur, they are unusual in natural populations (Wooten and Lydeard, 1990).
Native range: southern Alabama, throughout Florida and northward along the Atlantic Seaboard (Wooten and Lydeard 1990).
Known introduced range: Introduced to numerous countries around the globe on all continents except Antarctica.
Introduction pathways to new locations
Natural dispersal: Flooding events contribute to dispersal
Pet/aquarium trade: Obtained as feeder fish from aquariums
Local dispersal methods
Intentional release: Human disposal of aquarium fish into creeks, regurgitated by wading birds
On animals: Possibility of individuals caught in plumage of wading birds
On animals (local): Possibility of individuals caught in plumage of wading birds
Other (local): Human disposal of aquarium fish into creeks
Preventative measures: Copp et al, (2005) Risk identification and assessment of non-native freshwater fishes presents a conceptual risk assessment approach for freshwater fish species that addresses the first two elements (hazard identification, hazard assessment) of the UK environmental risk strategy. The paper presents a few worked examples of assessments on species to facilitate discussion. The electronic Decision-support tools- Invasive-species identification tool kits that includes a freshwater and marine fish invasives scoring kit are made available on the Cefas (Centre for Environment, Fisheries & Aquaculture Science) page for free download (subject to Crown Copyright (2007-2008)).
Chemical: Chemical control measures such as the application of Rotenone may be appropriate for small confined waterbodies, where impacts to non-target species can be minimised. Rotenone is indiscriminate, so non-target species ideally need to be removed prior to its application. Fish affected by Rotenone come to the surface to seek oxygen, so any remaining non-target species may be removed at this stage (Willis & Ling, 2000).
Physical: Physical control measures such as draining of a pond may be appropriate for small confined waterbodies, where impacts to non-target species can be minimised.
Gambusia is an opportunistic omnivore that feeds on a diverse range of terrestrial insects such as ants and flies that fall on the waters surface as well as aquatic invertebrates including bugs, beetles, fly larvae, zooplankton, filamentous algae and fragments of fruit and other plant tissues. Gambusia select their prey according to size, colour, movement and position in water column (Bence and Murdoch 1986; Lloyd 1984; Arthington and Marshall 1999)
Sexual. Internal fertilisation with embryos developing within the female. Livebearer. The reproductive cycle is primarily governed by photoperiod (Pen and Potter, 1991). 50-100 young per brood per female adult. Females have two to three broods per season (Howe 1995).
Individuals become sexually mature in under two months (McDowall 1996). Gestation period is between 21 and 28 days (Cadwallader and Backhouse 1983; McDowall 1996). Female gambusia have the capacity to store sperm from breeding season to breeding season (Howe 1995). Females can live for up to 15 months.
Principal sources: FishBase, 2004. Species profile Gambusia holbrooki Eastern mosquito fish
Compiled by: IUCN SSC Invasive Species Specialist Group
Updates with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment
Last Modified: Monday, 21 June 2010