The Plague Minnow Gambusia holbrooki (Girard, 1859) was first introduced into Australian waters in 1925. Early introductions were carried out in Sydney, Melbourne, Brisbane, and later Perth, by government agencies in an attempt to reduce the incidence of mosquitoes in the capital cities. G. holbrooki flourished, but no reports were made of any apparent ecological problems arising from its introduction.
World War II and the advent of the war in the Pacific resulted in heavy Allied troop movements between mainland Australia, New Guinea and the Pacific Islands. Malaria began to take a heavy toll, so the US Army instigated a means of mosquito control through the captive-breeding and introduction of the Western Gambusia G. affinis (Baird and Girard, 1853) throughout the south-west Pacific region. The Australian Army initiated a similar campaign using the already-available G. holbrooki to establish gambusia in creeks and wetlands near military bases and hospitals in eastern Australia. The Australian Army Malaria Unit was deployed to develop gambusia breeding ponds and to disperse the fish to suitable sites. Other methods of mosquito control were also employed.
By the end of WW II G. holbrooki was widely established throughout many parts of eastern Australia,but the program of captive breeding and release remained in place for several more years as many malaria-affected personnel were now resident in Australia. In the early 1960s the first reports of adverse environmental impacts of gambusia on native fish populations appeared, and these were quickly followed by reports of impacts on other organisms, such as frogs. Gambusia was always likely to become an environmental pest species once introduced into Australia. The need to control mosquitoes and mosquito-borne diseases during and following WW II was paramount, however, and efforts to do this greatly accelerated the spread of gambusia. The fish established in high densities in areas where undesirable environmental consequences later became apparent, precipitating the disaster for wildlife that we see today.