The Danube Fish Database: documenting species distributions across a major European river basin.

The Danube River Basin (DRB) harbors the highest documented fish species richness of any European river, yet native populations face increasing threats from physical infrastructures that impede longitudinal and lateral connectivity, unsustainable fisheries, the introduction of non-native species, and climate change. Spanning across 19 countries, the DRB presents conservation challenges that demand coordinated, transboundary data sharing. The present database compiles and standardizes fish occurrence datasets that have been previously unavailable, fragmented and often restricted by federal agencies, research institutes, and conservation organizations, integrating also data from sources such as the Global Biodiversity Information Facility, the Joint Danube Surveys, the European Fish Index, and national monitoring programmes. It contains 133,131 occurrence records across 114 fish species, representing 30 families and 17 orders, with a temporal range from 1856 to 2024, organized into 39 columns. By supporting fish community conservation, invasive alien species monitoring, and climate impact assessments, this database provides a vital resource for developing evidence-based management strategies in the DRB.