Biological invasions are one of the main global threats for biodiversity. The eastern mosquitofish (Gambusia holbrooki) is considered one of the 100 world worst invasive species due to its high adaptation capability to new environments. The focus of this analysis is to compare native USA mosquitofish populations and introduced European locations to detect genomic changes occurred during invasive process. The used methodology was the restriction-site associated DNA tags (RADtags) sequencing.