Stable isotope analyses reveal predation on amphibians by a globally invasive fish (Gambusia holbrooki)

Biodiversity loss caused by invasive species is particularly problematic in freshwater ecosystems, which are among the world's most threatened habitats. Invasive fish such as the eastern mosquitofish, <i>Gambusia holbrooki</i>, have been implicated in the decline of amphibians, which suffer high extinction rates globally. Although <i>G. holbrooki</i> is one of the most studied freshwater fish, its diet shows wide geographic variation and its impact on amphibian populations remains unclear. Stable isotopes ¹³C and ¹⁵N were used in 10 urban ponds in Sydney, Australia to compare the diet of <i>G. holbrooki</i> in January, April and May 2013 using a stable isotope mixing model. <i>Gambusia holbrooki</i> was carnivorous and fed on invertebrates (24–39%), tadpoles (25–32%) and conspecifics (20–45%). In contrast to previous studies, primary producers were a negligible part of <i>Gambusia holbrooki</i> diet (