Gambusia holbrooki
(eastern mosquitofish)

The eastern mosquitofish Gambusia holbrooki is an exotic fish, which is now widespread around the globe and is known to adversely affect native fish through competition and/or predation. G. holbrooki is known to impact upon native fish via competition with similar sized species, predation upon the fry and eggs of native fish, and by attacking all sized fish by aggressive fin-nipping, thereby leaving them susceptible to disease (Arthington, 1991). G. holbrooki can rapidly increase in population size due to its rapid maturation to breeding age (four weeks in summer) and high survival rate of young (Milton and Arthington, 1983; Lloyd et al., 1986; Lloyd, 1990).

The native habitat of mosquitofish is the lowland ponds, lakes and streams of southern USA (Casterlin and Reynolds, 1977). Mosquitofish are particularly adapted to exploiting inundated floodplains (Ross and Baker, 1983). G. holbrooki is abundant in near-shore environments, close to dense vegetation, and prefers sluggish waters to running water (Lloyd, 1987). Other habitat preferences include: shallow water, dark-coloured substrata, and subsurface vegetation (providing lateral rather than vertical concealment) (Casterlin and Reynolds, 1977; Arthington and Marshall, 1999). They are very adaptable and will live in almost aquatic habitats from fresh to hyper-saline, cold temperate to tropical waters (and artificially heated waters), inland, coastal and estuarine waters, and both still and slow-flowing waters. The species does seem to be poorly adapted to fast flowing waters which inhibits its ability to develop large populations (Lloyd, 1987).

Genetics

For more on the genetics of this species please see Yardley and Hubbs (1976) and Wooten et al. (1988).

Associations

Disturbed environments are prone to invasion from this species due to the fact that disturbed habitats can support large populations of invertebrate species (which tend to be pests, e.g. chironomids) and often lack other fish “due to harsh physical conditions” (Lloyd, 1987). Mosquitofish are typically more resistant to pollutants, including organic wastes, herbicides, insecticides, rotenone, phenols, heavy metals and radiation, than most other fish (Lloyd, 1987; Edwards, 2005). The ability of the species to survive genetic ‘bottle-necks’ and their ability to physiologically and genetically adapt to different environments is also important in their spread and success.

Environmental Requirements

Mosquitofish have invaded a wide range of habitats throughout the world including: hot springs, rivers, streams, lakes, swamps, billabongs, cooling pondages, rice fields, ornamental ponds, estuaries, near-shore marine habitats and salt lakes (Lloyd, 1987; Arthington and Lloyd, 1989).

Mosquitofish are found in waters from 0.5°C to 39°C, with a preference for warm waters of about 25°C (Otto, 1974), though Pyke (2005) suggests that mosquitofish prefer water temperatures between 31-35°C. Juvenile mosquitofish are more thermally tolerant than adults, allowing them to colonise and exploit warm patches of the environment with increasing growth, survival, and maturation rate. Mosquitofish can inhabit ice-covered waters (Hirose, 1976;Sasa and Kurihara, 1980) in Japan and hot bores (over 37°C) in central Australia (John Glover, personal communication, cited in Lloyd, 1987).

Environmental

• Biological control

General

• Laboratory use
• Pet/aquarium trade

Genetic techniques have been used to distinguish G. holbrooki and G. affinis in Australia.

For information on the morphology of G. holbrooki please see this species' factsheet on FishBase.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

SPS measures

All of these measures have been applied to prevent the spread of Gambusia in Australia. The Australian Quarantine Inspection Service (AQIS) has listed G. holbrooki as a high-risk species, highly likely to establish and spread more widely once introduced to new areas (Arthington et al., 1999). Predation by G. holbrooki has been listed as a key threatening process under the New South Wales Threatened Species Conservation Act 1995. The inappropriate spread of Gambusia by humans for the purpose of mosquito control remains a problem in spite of repeated cautionary advice over the past 20 years (Arthington and Lloyd, 1989). Gambusia has been recognised as a potential vertebrate pest in Australia and as such should be managed under the edicts of vertebrate pest policies, programmes, and legislation (Bomford, 2001; Bomford and Glover, 2004).

Early warning systems

Rapid response

Public awareness

Eradication

Containment/Zoning

Control

Cultural control and sanitary measures

Physical/mechanical control

Movement control

Biological control

Chemical control

IPM

Monitoring and Surveillance

08/08/08 Original text by:

Angela Arthington, Australian Rivers Institute, Room 1.09A, Environ. 2, (Building N13), Griffith School of Environment, Griffith University, Nathan QLD 4111, Australia

Lance Lloyd, Lloyd Environmental Pty Ltd, PO Box 3014, Syndal, Victoria, 3149, Australia