Changes in the distribution of the European mudminnow (Umbra krameri Walbaum, 1792) in Hungary over the last 50 years

The European mudminnow ( Umbra krameri Walbaum, 1792) is a relict wetland fish endemic to the Danube Basin, with Hungary representing the core of its historical distribution. We compiled published faunistic records, grey literature and standardised field-survey data from 1975–2025 to quantify long-term distribution changes across 12 Hungarian geographic regions and 200 documented localities. Confirmed persistent populations occur at 45.5% of historical localities (91 sites), including 17 “large” and 74 “small” populations. An additional 15 sites (7.5%) show only occasional recent records, whereas the European mudminnow has disappeared from 44% of its historically known localities. Most extant populations remain small and spatially fragmented. The Danube–Tisza Interfluve historically contained the highest number of localities (n = 57) and exhibited the greatest absolute loss (33 disappeared sites), primarily associated with hydrological degradation. In contrast, the Fertő–Hanság–Szigetköz Region currently represents the most important north-western refuge (21 persistent populations, including three large populations), whereas the Zámoly Basin is regionally extinct. Across all localities, invasion by the Amur sleeper ( Perccottus glenii Dybowski, 1877) (35% of sites) and documented desiccation (30.5%) were the two most frequently recorded threat categories. GLM applied to sites with known status (n = 194) showed substantially lower predicted persistence probabilities at sites affected by desiccation. At the national scale, desiccation emerged as the only clear independent predictor of reduced persistence, whereas the effects of other pressures appeared regionally heterogeneous and context-dependent. Surviving populations increasingly occur in artificial canal systems, indicating a marked shift from natural floodplain habitats towards secondary refugia. Integrated hydrological restoration, invasive-species control and genetically informed conservation management, including eDNA-based monitoring, are urgently required to prevent further contraction of this approximately 60-million-year-old Danubian endemic lineage.