Global and European regional assessment: Near Threatened (NT)
EU 27 regional assessment: Near Threatened (NT)

The Brook Barbel is endemic to Europe, where it is restricted to the northern Adriatic Sea basin in Italy and Switzerland. The distribution does not approach the range size thresholds for Vulnerable under Criterion B1 (extent of occurrence (EOO) < 20,000 km²) or D2, and Criterion B2 is precluded by its uncertain area of occupancy (AOO). The population size is believed to exceed mature 10,000 individuals, hence it does not approach the thresholds for Criteria C or D. There exists no quantitative analysis which would permit application of Criterion E.

There has been a suspected population size reduction based on a continuing decline in habitat quality might approach the threshold for Vulnerable under Criterion A2 (≥ 30% over the longer of 10 years or three generation lengths). As a result of this data uncertainty, Least Concern and Vulnerable are equally plausible Red List categories for the present assessment, and this species is assessed as Near Threatened (A2ce) both globally and for the EU 27 member states.

This species is endemic to the northern Adriatic Sea basin in Italy and Switzerland, where its range extends northward from the Marecchia River to the Brenta River and thus includes the Po River system. The precise limits of its current distribution within this range are somewhat unclear.

It was introduced elsewhere in Italy during the late 20^th century, e.g., to the Arno and Ombrone rivers, but did not become established at these locations.

This species' population size is unknown, but is expected to surpass the minimum threshold for Red List criteria (< 10,000 mature individuals). The current population trend has not been quantified, and the number of subpopulations is unclear.

Its abundance is understood to have declined significantly since the mid-20^th century, and this pattern is suspected to be ongoing in parts of Italy. In contrast, site-scale abundance is reportedly increasing in Switzerland, albeit this comprises only a small proportion of the overall range.

This benthic, rheophilic species inhabits the middle and upper reaches of subalpine headwater rivers and streams which are mostly located at altitudes of 800-1,000 m asl. Such habitats typically contain cool, clear, flowing water and mixed rocky substrata comprising gravel, cobbles, boulders and exposed bedrock.

The diet mainly comprises benthic macroinvertebrates. The maximum recorded lifespan is five years and adults reach sexual maturity at age 1-2+. The species is estimated to have a generation length of three years. This species is a fractional, polygamous spawner and the annual reproductive period extends from May and July, during which time adult individuals migrate to upstream spawning sites comprising riffles with coarse substrata.

In some tributaries of the Po River this species co-occurs and hybridises with the Italian Barbel (Barbus plebejus).

This species is threatened by river regulation and other forms of anthropogenic habitat degradation. In particular, the construction of large dams plus smaller weirs and other barriers has severely altered natural flow and sedimentation regimes, blocked migration routes, fragmented subpopulations, and reduced the extent  of suitable habitat for all life stages. Hydroelectric dams have created unnatural fluctuations in discharge and water temperature (hydropeaking and thermopeaking) which bring about artificial dewatering of downstream river stretches and loss of stable nursery habitat for juveniles. Furthermore, the combined effect of hydropeaking, dam flushing operations, changes in land use, and the removal of riparian vegetation is likely to have increased accumulation of fine sediments at some spawning sites, plausibly impairing the hatching and survival rates of eggs and larvae.

The quality of habitat has been further diminished by bank stabilisation, channelisation and other efforts to enhance flood protection or exploit water resources. Unregulated water abstraction may constitute a particular threat to this species' upstream spawning and nursery sites, some of which may also have been damaged by the industrial extraction of riverine gravel or other sediments for urban development.

The Brook Barbel is also threatened by diffuse and point source agricultural, domestic and industrial pollution, which has at some locations reduced the extent and quality of habitat due to eutrophication or the release of toxic substances. Sources of contamination can be particularly impactful when river discharge is reduced during the summer.

Non-native Brown Trout (Salmo trutta) and Rainbow Trout (Oncorhynchus mykiss) have been intensively-stocked throughout much of its range for several decades, and may contribute to site-scale declines through predation. Unlike some congeners, this species has not been impacted by introgressive hybridisation with introduced non-native barbels due to its relatively specialised habitat requirements.

This species is not used or traded.

This species is included (originally as Barbus meridionalis) in Appendix III of the Bern Convention and Annexes II and V of the European Habitats Directive.

It was assessed as Endangered for the 2022 Red List of Italian Vertebrates, and as Vulnerable for the 2022 Swiss National Red List.

It occurs within the boundaries of numerous protected areas, some of which are included in the European Union's Natura 2000 network.

Efforts to coordinate ex situ breeding programmes have been ongoing since the mid-1990s, but have met with limited success. The European Union co-funded LIFE project LIFE13 NAT/IT/001129 BARBIE ran from 2014 to 2018, and aimed to preserve and restore native populations of this species and the Italian Barbel within 14 protected areas in the Emilia-Romagna region of northern Italy (Po River system). The project included plans to eradicate non-native fish species alongside ex situ breeding and stocking efforts in locations from where the two species had previously been extirpated, and monitoring was due to continue post-project. The results had not been published at the time of this assessment.

A deeper understanding of this species' current abundance, distribution, population trend and life history, particularly the identification of key spawning sites, would likely prove useful in the development of future management efforts.