Dispersal behaviour of fish expanding their range is an important component of invasion success and can evolve along dispersal pathways. Understanding the movement biology of invasive species during the spread phase of a new invasion is important for developing targeted management strategies. This study determined the extent and movement patterns of two tilapia species, Oreochromis mossambicus and Pelmatolapia mariae, in the Mitchell River catchment, northern Australia, during the spread phase of the invasion. Tilapia were only found in three locations within one sub-catchment of the Mitchell River. Strontium isotopes of tilapia otoliths revealed different movement patterns among these three locations, with active dispersal to one of the locations from both other locations. Movements made by P. mariae mostly occurred within the first two years of life. These movement patterns demonstrate active habitat seeking behaviour, mostly by juveniles, that lead to the successful establishment of tilapia at new locations within a catchment following introduction. The movement patterns revealed in this study were used to recommend priority management actions to limit the risk of tilapia spreading to vulnerable floodplain habitats and other river systems in the Gulf of Carpentaria. These include monitoring within the sub-catchment containing established tilapia and control measures applied to the established local populations to limit population growth, limiting the risk of downstream spread by reducing dispersal probability.