Context. Present-day distribution records show that Oxyeleotris lineolata (sleepy cod) has colonised many ephemeral streams and refugial waterholes of the Cooper Creek catchment in the Lake Eyre Basin within a decade of the first record or capture. When introduced to new habitats outside its natural range, this species is considered to be a serious conservation risk to native fish species.

Aims. The present study aims to document the transport, establishment, colonisation and integration of O. lineolata in the Lake Eyre Basin, and quantify its impact on native fish assemblages.

Methods. Fish samples were taken annually in 21 waterholes between 2011 and 2016, by using a combination of single- and double-winged fyke nets. We collected novel diet and life-history information from 242 O. lineolata individuals across their known distribution.

Key results. Abundance, length distribution and life-history information suggested a ‘colonising front’ moving downstream, across state jurisdictional boundaries and into the Coongie Lakes Ramsar site. Oxyeleotris lineolata diet is most similar to that of two native generalist invertivore–piscivores and preys on several native fish species. With a derived longevity in excess of 15 years and a life-history strategy that combines batch spawning, high fecundity and parental care (i.e. high juvenile survivorship), there is real potential for O. lineolata to dominate fish assemblages in waterholes that provide refuge for native fishes during dry periods.

Conclusions. The present study showed that O. lineolata has the potential to negatively influence native fish assemblages through both competition and predation in refugial waterholes. Eradication of O. lineolata from the Cooper Creek catchment in central Australia is highly unlikely, given its widespread distribution, the remoteness of the receiving landscape and a current lack of resources to monitor spread and attempt eradication at the moving front of the Cooper Creek population.

Implications. Achieving greater awareness of the potential impacts of introducing or spreading non-native species is an important first step towards preserving the native fish fauna of the Lake Eyre Basin. Further research is warranted to fully understand the current and potential future distribution of O. lineolata in the basin, its biological and ecological requirements, and influence on native fish species and assemblages.