The potential distribution of tropical fish species in Eastern Europe—Gambusia holbrooki Girarg, 1859 (introduced for biological control) and Poecilia reticulata Peters, 1859 (aquarium species, found in wastewaters of big cities)—tends to be of particular interest in terms of global climate change. After GIS modeling of our own data and findings listed in the GBIF databases (2278 points for G. holbrooki and 1410 points for P. reticulata) by using the Maxent package and 18 uncorrelated variables of 35 Bioclim climatic parameters from the CliMond dataset, it was found that by 2090, guppies will appear in the south of Ukraine (Danube River estuary, as well as in several places in the Caucasus and Turkey with habitat suitability of >0.3–0.5). G. holbrooki will also slightly expand its range in Europe. Limiting factors for G. holbrooki distribution are as follows: bio1 (annual mean temperature, optimum +12–+23 °C) and bio19 (precipitation of coldest quarter (mm)). Limiting factors for guppies are as follows: bio1 (optimum +14–+28 °C), bio4 (temperature seasonality), and bio3 (isothermality). Guppies, unlike G. holbrooki, prefer warmer waters (correlation 0.02). Such thermophilic fish species do not compete with the native ichthyofauna, but they can occupy niches in anthropogenically transformed habitats, playing an important role as agents of biological control.