Global and European regional assessment: Least Concern (LC)
EU 27 regional assessment: Least Concern (LC)

This species does not approach the range thresholds for Vulnerable under Criterion B (extent of occurrence (EOO) < 20,000 km², area of occupancy (AOO) < 2,000 km²) or D2. Although the quality of habitat is estimated to be declining, there is no evidence that any population size reduction approaches the threshold for Vulnerable under Criterion A (≥ 30% over the past ten years or three generations). The population size does not approach the thresholds for Vulnerable under Criterion C (< 10,000 mature individuals) or D1, and there exists no quantitative analysis of extinction probability which would permit application of Criterion E.

Therefore, the Danube Streber does not currently meet the thresholds for any Red List criteria, and it is assessed as Least Concern both globally and for the EU 27 member states.

This species is native to the Danube and Dniester rivers in Central and Southeastern Europe. Its precise distribution within these systems is unclear due to a lack of recent occurrence data for many areas.

This species' population size is unknown, but it is believed to exceed 10,000 mature individuals. The current population trend has not been quantified, and the number of subpopulations is unknown.

There is little doubt that its overall abundance has declined significantly since the mid-19^th century (see 'Threats). It is today considered to be rare in most countries within its range, e.g., Czechia, Slovakia, Moldova, where historical records suggest that it was once far more widespread. In Bavaria, Germany, it is estimated to occupy c. 7% of its historical distribution.

This strictly benthic, rheophilic species inhabits clean, cool, well-oxygenated river reaches with unclogged substrata of coarse gravel, cobbles and boulders.

It is typically found in riffles and runs at intermediate depth (0.3–1.8 m) in stretches with moderate to fast water flow (0.3-0.9 m/s), and thus differs from the congeneric and sympatric Zingel (Zingel zingel), which tends to be found in deeper glides with slower currents and fine substrata.

It is territorial and believed to naturally form low density subpopulations.

The annual reproductive period extends from March to May, during which period male individuals develop white tubercules on the head. Sexual maturity appears to be reached within the first year of life, and the average lifespan is estimated at two to three years.

Although members of this genus are often said to be nocturnal, studies have revealed that the congeneric Rhône Streber (Zingel asper) is more active during daylight hours.

Its dietary preferences do not appear to have been studied in depth, but the Rhône Streber feeds on epibenthic invertebrates typical of unclogged lotic environments, especially Diptera, Ephemeroptera, Plecoptera and Trichoptera.

This species' decline has been driven by habitat modification and pollution from agricultural, domestic and industrial sources.

In particular, the construction of dams and other barriers has created chains of artificial lakes, causing subpopulations to become fragmented and significantly reducing the extent of suitable habitat by altering water quality and hindering natural flow, sedimentation and water temperature regimes.

The results of experimental trials have also demonstrated that Zingel species are unable to pass even very low obstructions, and molecular analyses have revealed a loss of genetic diversity in upper Danube subpopulations that have probably been driven directly by their isolation due to barriers.

Furthermore, widespread regulation of channels and banks has eradicated entire subpopulations through the loss of vital morphological features such as rapids and riffles, while harvesting of gravel from riverbeds has removed extensive stretches of suitable habitat.

Certain land management practices and the periodic flushing of artificial dam lakes have resulted in increased soil erosion and siltation, leading to gravel beds becoming clogged and further reducing quality of its preferred habitats.

In addition, a combination of channelisation, hydropeaking from hydroelectric dams and sediment clogging has driven a decline in the biodiversity of macrobenthic communities and has plausibly interfered with prey availability (see 'Habitats and Ecology').

This species is also sensitive to anthropogenic contamination, which in the Danube system peaked during the latter period of the 20^th century. Although there has been a general decrease in the levels of organic pollution and hazardous substances in the river's main stem since the 1990s, high pollutant loads and eutrophication continue to be of concern in many tributaries throughout the catchment.

This species is not used or traded.

This species is included in Appendix III of the Bern Convention and Annex II of the European Union Habitats Directive (in the latter originally as Zingel spp. except Zingel asper and Zingel zingel).

It is nationally-protected and included in the National Red Lists or Red Data Books of a number of countries within its range, e.g., it has been assessed as Vulnerable in Croatia, Endangered in Austria and Slovenia, and Critically Endangered in Czechia.

Since the European Union Habitats Directive was adopted in 1992, most member states to which the Danube Streber is native have designated Special Areas of Conservation (SACs) for its specific protection. Numerous subpopulations thus occur within the boundaries of protected areas, many of which are included in the European Union's Natura 2000 network.

Many dams and other artificial barriers in the Danube River are equipped with fishways to facilitate both upstream and downstream passage, but these typically do not meet this species' requirements in terms of flow velocity, water depth and connection to the river bed.

In the European Union member states, it is plausible that this species may have benefitted from improvements in the ecological conditions of waterways driven by efforts to comply with the Water Framework Directive 2000/60/EC.

It has been little-studied throughout the majority of its range, and it is recommended that future research efforts should focus on establishing its current distribution and population trend in addition to identifying sites or subpopulations that might be of immediate conservation concern.

Some subpopulations exhibit marked genetic divergence, and this should be taken into account when considering appropriate management actions.