Freshwater ecosystems in Japan are increasingly threatened by nonnative fish species, yet the potential impacts of future climate change on their distribution at a national scale is poorly understood. In this study, we present a nationwide, multi-species assessment of the current and future invasion patterns of freshwater fishes in Japan, based on species distribution modelling. Occurrence records were compiled from national databases and literature sources, and species distributions were modeled using MaxEnt with climatic, hydrological, topographic, and human-related predictors. We then projected future suitable habitats under two climate scenarios (SSP245 and SSP585) across four time periods spanning the 21st century.
The model projections consistently indicate an expansion of suitable habitats for freshwater invasive fishes under future climate change, with stronger changes under the high-emission scenario (SSP585) than under moderate-emission scenario (SSP245). Invasion risk shows pronounced spatial heterogeneity, with hotspots concentrated in central and southern Japan, particularly in lowland regions such as the Kanto Plain, and along major rivers. When occurrence data were aggregated across species, both projected invasive fish richness and mean suitable area increased throughout the 21st century, suggesting an overall intensification of invasion pressure. Across species, invasion patterns were primarily shaped by climatic drivers related to high temperature, low temperature, and precipitation, although the relative importance of these drivers varied markedly among species. Of the 20 invasive species evaluated, 15 showed an increase in suitable area under future climate change, while the remaining five species exhibited limited change or contraction.
Overall, this study has identified potential invasion hotspots and species of concern across Japan, providing a spatially explicit reference for understanding future invasion risks of freshwater fishes under climate change.