Intra-country introductions unraveling global hotspots of alien fish species

Alien or non-native species are defined as species living outside their natural distributional ranges. The spread of alien species is increasing globally as a result of rapid technological advances and globalization. Recent investigations have estimated global hotspots of alien established species on the basis of geopolitical boundaries, including Dawson et al. (in: Nat Ecol Evol 1:186. 10.1038/s41559-017-0186, 2017). In particular, these investigations do not consider Intra-Country Established Alien Species, i.e., successful introductions that occur among regions within the same country. In continental countries such as Brazil, the USA and China, studies excluding Intra-Country Established Alien Species (IEAS) waste essential information. Here, we argue that researchers should also consider intra-country introductions when estimating and addressing the risks of alien introductions. By using detailed data for freshwater fish including IEAS in large countries, we demonstrate that novel hotspots for IEAS have arisen worldwide. We illustrate emblematic examples of IEAS, as well as their vectors and negative impacts, to demonstrate the range of impacts that might be missed when excluding IEAS data from analysis. We recognize the need for generalizations, but generalizations based on incomplete data can misinform conservation efforts, particularly in megadiverse regions. Ignores IEAS influences how we count non-native species, invasions and perceive invisibility and impacts. Consequently, upcoming records and analysis of invasion patterns and management of aliens and EAS global hotspots must account for such biases in quantifying the IEAS portion.