A study analyzing global freshwater fish invasions reveals that non-native fish species are more likely to establish when closely related to native species. This finding contradicts Darwin's naturalization hypothesis, suggesting that the presence of close relatives indicates suitable habitats rather than intensified competition. The research, based on a comprehensive database of 14,953 freshwater fish species across 3119 river basins, identifies global hotspots for exotic and translocated non-native fish. The study shows that both types of non-native fish are more likely to occur when phylogenetically related to native species, consistent across measures of phylogenetic relatedness, biogeographical realms, and countries. The results indicate that phylogenetic relatedness is a key factor in predicting the establishment of non-native fish species, with closely related species more likely to succeed. The study also highlights the importance of considering native species richness and phylogenetic diversity in understanding fish invasions. The findings suggest that the presence of close relatives and high native species richness are indicators of a higher likelihood of non-native fish occurrence, rather than competition. The study emphasizes the need for further research to assess the role of phylogenetic relatedness in fish invasions across different spatial scales and environmental gradients. The results provide valuable insights for understanding and predicting future fish invasions in freshwater ecosystems.A study analyzing global freshwater fish invasions reveals that non-native fish species are more likely to establish when closely related to native species. This finding contradicts Darwin's naturalization hypothesis, suggesting that the presence of close relatives indicates suitable habitats rather than intensified competition. The research, based on a comprehensive database of 14,953 freshwater fish species across 3119 river basins, identifies global hotspots for exotic and translocated non-native fish. The study shows that both types of non-native fish are more likely to occur when phylogenetically related to native species, consistent across measures of phylogenetic relatedness, biogeographical realms, and countries. The results indicate that phylogenetic relatedness is a key factor in predicting the establishment of non-native fish species, with closely related species more likely to succeed. The study also highlights the importance of considering native species richness and phylogenetic diversity in understanding fish invasions. The findings suggest that the presence of close relatives and high native species richness are indicators of a higher likelihood of non-native fish occurrence, rather than competition. The study emphasizes the need for further research to assess the role of phylogenetic relatedness in fish invasions across different spatial scales and environmental gradients. The results provide valuable insights for understanding and predicting future fish invasions in freshwater ecosystems.