Biology and ecology of introduced Phalloceros harpagos Lucinda in south-western Australia: comparisons with the invasive poeciliid Gambusia holbrooki Girard

[Truncated abstract] Fishes are one of the most widely introduced aquatic taxa and freshwater systems worldwide have been deleteriously affected by introduced fishes through mechanisms that include predation and resource competition. My thesis compares the biology and ecology of two fishes from the family Poeciliidae introduced into south‐western Australia. Phalloceros harpagos is a little‐researched South American poeciliid that is not a commonly introduced species and, at present, is only well established in urban aquatic habitats of south‐western Australia. In contrast, Gambusia holbrooki is a highly invasive poeciliid with a worldwide distribution and an extensive literature of biology and ecological impacts. The trophic position, female reproductive biology and behaviour of these poeciliids were compared to investigate if P. harpagos has the potential to overpopulate aquatic habitats, and impact upon endemic fish populations, as successfully as G. holbrooki in south‐western Australia. Dietary data from gut content analysis and stable isotope analysis (δ15N and δ13C) were utilised to calculate the trophic position of P. harpagos, G. holbrooki and native fishes. The diets of all fish groups were concordant with published literature, with P. harpagos consuming principally vegetal matter and silt/biofilm with smaller quantities of algae and aquatic invertebrates. Gambusia holbrooki, Galaxias occidentalis and Bostockia porosa were omnivorous though consumed higher quantities of aquatic and terrestrial invertebrates, and also small fishes. δ15N signatures and trophic position calculated from isotope data suggested that the smaller quantities of aquatic invertebrates consumed by P. harpagos were readily assimilated and that the species occupied a similar trophic position to other fish groups that almost entirely consumed aquatic and terrestrial fauna.