*3.2. Limiting Factors for G. holbrooki Distribution*

On the contrary, mosquitofish can coexist in open water bodies outside the warm wastewaters of large cities and anthropogenic areas, in roadside water bodies (Figure 1B) in western and southern parts of Europe, as well as in Ukraine—in the Odessa region and the Crimea [32]. As a result of GIS modeling, it was revealed that the most important factors

(percent contribution) limiting the distribution of *G. holbrooki* in Europe are: bio21 Highest weekly radiation (W m−2)—26.2%, bio19 Precipitation of coldest quarter (mm)—18.6%, bio1 annual mean temperature—14.7% has the optimum—+12–+24 ◦C (mean—+16.5 ◦C), within the native range of +15–+24 ◦C (mean—+19.5 ◦C, Figure 2, [28]). This fish is able to reproduce throughout the year as long as the water temperature is above +15 ◦C (April– November). An interesting observation is that at a water temperature below +10 ◦C *G. holbrooki* burrows into the silt and falls into a suspended anabiosis [33]. During severe winters when reservoirs are bound with ice, *G. holbrooki* perishes in great numbers. For instance, this species died en masse as a result of cold winter in Sochi in 2020 [34,35].

**Figure 2.** Plot variable bio1 Annual mean temperature (◦C, CliMond, 1975 (1970–2000)) from: Pec—*P. reticulata*; Gam—*G. holbrooki*; nat—native range; W—World areas.

### *3.3. Niche Clustering*

Using the clustering algorithms (a statistical tool which explains the difference between the variables that describe climatic conditions) for visualizing the Hutchison's duality (Kmeans clustering, Colwell and Rangel 2009) it was shown that the native range of American alien fish species differs in bioclimatic parameters (Figure 3). Therefore, understanding such perspectives and conditions is very important for interpreting expansion of the species range in future. Therefore, the preference for a warmer temperature regimen (Figure 2), unpretentiousness, the possibility of live birth and great popularity among fans of exotic aquacultures make it possible to "expect" more favorable conditions during climate warming. And it is even possible to adapt to new conditions.
