Invasive introduced species are a leading cause of biodiversity loss and global change. Understanding the ecological impacts of introduced species and how abiotic factors mediate their invasive success is of enormous conceptual and applied importance. The mosquitofish (Gambusia holbrooki) is among the 100 worst invasive species and has been shown to displace a number of native amphibian and fish species. The host research group has experimentally demonstrated that salinity mediates the resource and interference competition between mosquitofish and an endemic Mediterranean fish (Aphanius fasciatus). The post-doc candidate has shown that water flow affects the mating behaviour in a similar poeciliid fish (the guppy, Poecilia reticulata). Using a range of theoretical (modelling, biostatistics, information capture), experimental (field and aquarium studies) and ecological (surveys, environmental measurements) techniques we aim to: i) experimentally test the competition between G. holbrooki and an endemic, threatened cyprinid (Squalius laietanus); ii) test whether water flow mediates this competition; and iii) conduct a meta-analysis reviewing the ecological impacts of Gambusia holbrooki and the factors that mediate them. We anticipate that the research will be published in top journals such as Oecologia or Animal Behaviour, given our previous papers on the topic and the complementarity of our expertise. This project provides clear benefits to the profile of the researcher and the research group and to the recognition of European excellence so greatly enhancing the potential for permanent European reintegration for the researcher.