Ecological similarity governs non-native fish establishment while human pressure and native diversity shape invasion richness.

Biological invasions by non-native fish species pose a major threat to global freshwater ecosystems. However, our understanding of why invaders establish in some communities but not others (i.e., occurrence probability) and why some communities harbor more invaders than others (i.e., invasion richness) remains limited. Here, we combine species- and community-level analyses across taxonomic, phylogenetic, and functional dimensions to investigate both the occurrence probability and invasion richness of exotic and translocated fish species across nearly 3000 North American freshwater fish communities. We found that ecological similarity between non-native and native species primarily governed non-native fish establishment, with invaders more likely to succeed when closely related to native species. In contrast, invasion richness was largely promoted by human pressure, while native diversity reduced richness specifically for translocated species. Additionally, both the occurrence and richness of invaders increased toward lower latitudes. Together, these findings highlight the distinct yet complementary roles of environmental filtering, human activities, and biotic interactions in shaping freshwater fish invasions.