A biogeographical survey of southern Manitoba determined the present distribution of the stonecat (Noturus flavus), a recent invading species, and placed an approximate timing of its arrival. Habitat and dietary comparisons between stonecats, longnose dace (Rhinichthys cataractae) and burbot (Lota lota) were made to evaluate interactions between these species. In the Assiniboine, Little Saskatchewan and Souris Rivers, presence of stonecats close to the base of dams indicates that the species has dispersed as far as possible in this drainage. Sampling upstream of these dams in similar habitat suggests arrival in Manitoba occurred in the mid to late 1960s. While stonecats and longnose dace are common in riffle habitats, interactions are minimal. Stonecats are nocturnal and have a more diverse diet, with foraging activity coinciding with prey availability. Longnose dace appear to be mostly diurnal, although foraging plasticity was exhibited. Diet diversity of dace is low, with two prey qpecies constituting most of the diet. Stonecats and longnose dace also segregate habitat spatially, with the latter occupying shallower habitats with faster wafer velocities. Burbot are nocturnal, but differs from the stonecat in diet selection. Invading from the more speciose Mississippi River drainage, the stonecat has co-adapted with all but one of the species in the Red/Assiniboine watershed. As the only riffle-dwelling Noturus species in the drainage, interactions due to similarities in morphology are low. These factors may have contributed to the successful invasion of the stonecat in Manitoba.