Gambusia or mosquitofish

  • Gambusia or Mosquitofish: restricted noxious fish
    Gambusia or Mosquitofish: restricted noxious fish
  • Drawing of a female gambusia or mosquitofish
    Drawing of a female gambusia or mosquitofish

General information

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

Instead, they have had a detrimental effect on native fish through competition for resources and their aggressive behaviour. They have a habit of nipping the fins of other fish, regardless of size differences. They also prey on the eggs and larvae of native fish and frogs.

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

Scientific name                                    

Gambusia spp

  • live-bearing fish                                                            
  • small fish, growing to less than 7 cm with most only reaching 3 or 4 cm                                                            
  • they are large-scaled and stocky-bodied                                                            
  • have adapted to living and feeding at or near the surface of the water                                                            
  • colour varies with habitat but usually they are dark grey or olive on the head and back, becoming lighter on the belly                                                            
  • faint pigment spots on the fins and under the eyes.                                                            
  • inhabit warm, fresh and brackish waters at low elevations                                                            
  • can withstand environmental conditions that native fish cannot, such as high temperatures and low oxygen, but they are sensitive to high salinity.                                                            
  • have a varied diet feeding on insect larvae, insects, plants, worms, crustaceans, snails, frog eggs and small fishes.                                                            
  • freshwater fish                                        
  • commonly found in lakes and still or slow-flowing streams.                                        
  • frequently found around the edges or among freshwater plants.                                        
  • generally inhabit warm, fresh and brackish waters at low elevations.                                        
  • introduced to eastern Australia in 1929 as a mosquito control agent because they thrive in calm, shallow, vegetated waters where mosquitoes lay their eggs                                        
Life cycle                                    
  • females mature at about 18-20 mm, which is 4-6 weeks of age                                                            
  • they can produce up to 315 young per season                                                            
  • produce small broods at frequent intervals, thereby increasing reproductive output and survival of the young                                                            
  • breeding season varies between 2-9 months                                                            
  • day-length is believed to determine the timing of the reproductive cycle.                                                            


  • have the potential to rapidly outnumber native fish and dominate aquatic communities                              
  • can survive a range of environmental conditions which native fish find difficult to cope with.                              
  • have many traits which make them a good invader such as high reproductive potential, flexible diet, broad environmental tolerances and low vulnerability to predation due to burrowing habit                              
  • are aggressive and nip the fins of other fish species as well as eat their eggs                              
  • highly successful as they mature early, have a high survival rate of fry and a large annual number of broods                              
  • also able to gulp air from the surface when there is low oxygen in the water.                              


  • loss of favourite fishing locations due to invasion.                              
  • Biosecurity Queensland advocates the ethical euthanasia protocols recommended by the 2001 ANZCCART publication: Euthanasia of animals used for scientific purposes. The most appropriate method may involve stunning the fish via a sharp blow to the back of the head just above the eyes. When applied correctly, this causes brain destruction—the fish’s gill covers should stop moving and its eyes should remain still                    
  • intensive fishing may have the potential to reduce pest fish numbers in small enclosed waterbodies, but it is very unlikely that fishing alone is an effective long-term control measure.                    


  • poisons have been used to eradicate 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
  • it must not be kept, fed, given away, sold, or released into the environment without a permit          
  • if caught these species must be immediately humanely killed and disposed of responsibly away from the water body          
  • by law, everyone has a general biosecurity obligation (GBO) to take reasonable and practical steps to minimise the risks associated with restricted noxious fish under their control.          

Further information

Last updated 01 July 2016