The ecological requirements and distribution of the native and non-native freshwater fish species of the Mugla Province were studied between 2009 and 2011. In total, 19 fish species including 5432 specimens were collected from 17 water bodies. Almost 40% of the fish were from non-native species, which were encountered frequently only from four water bodies. Squalius fellowesii was by far the most abundant species followed by Lepomis gibbosus and Ladigesocypris ghigii. Canonical correspondence analysis (CCA) explained 76% of the variation (first axis) between species and environmental variables, amongst which altitude, electrical conductivity and water temperature were the most influential. Based on habitat similarities, unweighted pair group means analysis (UPGMA) separated species into four clusters. Results revealed that species' optimum levels and ecological tolerances can be species-specific, even though non-native and widespread endemic species across the basin tended to have higher tolerance ranges for different environmental variables.