The Red List Threats to European Freshwater Fishes—Spatial Patterns and Knowledge Gaps ^†

Freshwater fish species comprise 40% of all fish diversity and provide multiple ecosystem services. Recently, several populations of this faunal group have faced declines and range contractions due to several threats. The Red List of Threatened Species, established by the International Union for Conservation of Nature (IUCN), is the most comprehensive system for evaluating species’ risk of extinction and holds information on the species’ populations, distribution, ecology, and threats. This work aims to use this database to (1) identify the major threats to European freshwater fishes; (2) portray the geographical patterns of threat incidence with species richness, conservation status, and migratory phenology; and (3) identify the knowledge gaps in terms of valid published scientific literature supporting the threat data in the IUCN Red List database. The analysis includes 434 species, of which 41.2% are threatened, accounting for 837 threats, whereas only 11 register a valid and published scientific output. “Resident” was the migratory phenology with the highest percentage of threatened species (46.3%), and “Dams & water management/Use” was the most frequent (>50%) threat type. Across Europe, there is a high level of imperilment in freshwater fish species, with a particular incidence in southern regions and some coastal areas. Southern Europe, particularly the Iberian Peninsula, has a comparatively low species richness but a high proportion of threatened species with a high threat incidence. Overall, only 1.6% of the species and 1.3% of all threats identified are supported by valid published scientific literature. In sum, the present level of imperilment of European freshwater fish fauna is high, particularly in Iberia, and river network fragmentation will likely be the most challenging threat to future restoration efforts. The lack of valid scientific support for the IUCN Red List assessment affects its reliability and may hamper efforts of threat mitigation and species conservation.