Key words: Eastern Gambusia, aggression, pest fish, Native Fish Strategy.
Threats and Impacts: Introduced to Australia in 1925 as a potential mosquito control agent, the fish Gambusia (Gambusia holbrooki) (Figs 1 and 2) is now present in almost every major Australian drainage, including the Murray-Darling Basin. Gambusia are extremely aggressive, harassing, predating and attacking native fish; and are thought to also pose a significant threat to many amphibians and invertebrates.
Broad aim, specific objectives and methods: This project explored in aquaria how aggressiveness of Gambusia changed according to the relative abundance of two native fish species (western carp gudgeon Hypseleotris spp. and juvenile Golden Perch Macquaria ambigua). Five treatments were run involving combination of Gambusia to native fish ratios and temperatures. The project was designed to improve understanding of how Gambusia might behave when it colonises new areas and how behavioural responses might be affected by efforts to control their numbers.
Figure 1: Female Gambusia. Note that all fish are in gravid condition. (Photo courtesy of Tarmo Raadik.)
Figure 2: Mature female Eastern Gambusia (photo courtesy of Tarmo Raadik)
Findings: The study found that Gambusia were highly aggressive towards both species of native fish and that aggressiveness increased when Gambusia were outnumbered by native fish. The study also found that the type of aggressive behaviour by Gambusia (e.g. biting or chasing) was specific to the native species it was interacting with. Gambusia were shown to dominate the available habitat within the tank very shortly after introduction. The high aggression and dominance behaviour exhibited by Gambusia when outnumbered assist this species when invading new habitats and may also have implications for eradication efforts aimed at this invasive species.
Lessons learned and future directions: The increased aggression by Gambusia when outnumbered potentially means that control efforts that reduce the abundance of Gambusia but don’t fully eradicate them may not be beneficial to native fish in some cases. The research suggested that aggressive interactions from Gambusia may not decrease as a result of eradication efforts.
Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy.
Contacts: Dr Andy Moore, Department of Agriculture Fisheries and Forestry. Tel: + 61 2 6272 3090, Email: anthony.moore@daff.gov.au.
Link: http://www.finterest.com.au/wp-content/uploads/2013/07/MD1224%20Gambusia%20Aggression.pdf
EMR Project Summaries 