Non-native freshwater fishes may become one of the dominant species in still and slow running waters and may impact whole ecosystem. One such species is the pumpkinseed Lepomis gibbosus, which has become widely distributed throughout Western Europe occurring primarily lakes and reservoirs. Although the species is known to have existed at least for four decades and expanded its distribution range in Turkish waters widely, virtually there is no study on the factors behind the species' establishment success. We hypothesized high environmental tolerance as well as high population structuring result in more successful establishment of pumpkinseed in new environments. We sampled three reservoirs, one canal and one stream located longitudinally along western part of Turkey to test this hypothesis. Optima (uk) and tolerance (tk) levels of the species were calculated with weighted averaging values for several measured environmental factors. Invasiveness of pumpkinseed populations was determined with the model proposed earlier examining the relationship between juvenile growth and age at maturity. The phylogenetic network of mitochondrial haplotypes was constructed for Turkish populations and other populations of pumpkinseed from native (North America) and introduced range (Europe). Potential invasiveness of pumpkinseed populations in Turkey was categorized as invasive in one location (Saricay stream) and transitional in other locations. Environmental tolerance values were higher in southern populations. Likewise phylogenetic network showed that the Turkish populations have unique haplotypes, which were originated from native North American populations suggesting a high differentiation in haplotypes. Results clearly demonstrate the effect of environmental factors on genetic structure and the establishment success of pumpkinseed.(C) 2014 Elsevier Ltd. All rights reserved.