This species was formerly considered native to a series of river systems draining from eastern Italy to the Adriatic Sea, but these subpopulations were in 2021 reassigned to the congeneric Italian Barbel (Barbus plebejus), Samnite Barbel (B. samniticus) and Fucine Barbel (B. fucini). Subpopulations inhabiting rivers south of the Tiber system on the Tyrrhenian slope were also reassigned to the Fucine Barbel (Lorenzoni et al. 2021).

The Horse Barbel is a benthic species which is endemic to the western Italian Peninsula. It is suspected to have undergone a population size reduction of at least 50% within the past decade, primarily driven by the ongoing spread of non-native taxa, as well as declines in habitat quality. Therefore, this species is assessed as Endangered under Criterion A (A2ace).

This species is endemic to the western Italian Peninsula, where its range extends southward from the Magra to the Tiber (it. Tevere) river systems.

It is understood to have been translocated outside of its natural range, since molecular analyses have revealed signals of introgressive hybridisation with the congeneric Italian Barbel (Barbus plebejus) in the Brenta River (Adriatic Sea basin).

The origin of introgression between the same two species further south along the Adriatic coastline (in the Metauro, Cesano and Esino rivers) could be the result of anthropogenic translocation, natural dispersal during historic periods of trans-Apennine connectivity, or a combination of these factors.

This species' population size is unknown, but is understood to exceed the minimum threshold for Red List criteria (< 10,000 mature individuals). The number of extant subpopulations is unclear.

Its overall abundance has been undergoing a continued decline since the mid-1990s. This reduction is particularly evident in the Tiber and Arno river systems, of which the main stems and major tributaries are now dominated by hybrid individuals and non-native taxa (see 'Threats'). It is also understood to be declining rapidly in the Ombrone and lower Albegna rivers (A. Carosi and M. Lorenzoni, pers. comm.). In the last 10 years the population is suspected to have declined by 50%.

This relatively large-bodied, benthic species inhabits deeper stretches of the upper and middle courses of flowing, well-oxygenated rivers with sandy to rocky substrata.

Males become sexually mature at 2-3 years, and females at 4-5 years of age. Spawning takes place in shallow upstream riffles from April to August, peaking in May and June.

Its diet comprises aquatic invertebrates, detritus, and occasionally smaller fishes.

This species' decline has primarily been driven by the ongoing spread of non-native taxa which were ostensibly introduced to supplement recreational fisheries, particularly the Common Barbel (Barbus barbus) which exhibits strong ecological overlap and hybridises with the Horse Barbel. In the Tiber River system, the Common Barbel has rapidly expanded its range since it was first detected during the late 1990s, leading to a near-complete loss of Horse Barbel in the middle reaches of the main stem and most major tributaries, e.g., the Paglia, Topino, Nestore and Chiascio rivers. In some of these systems, artificial barriers such as dams and weirs have restricted the upstream dispersal of hybrid lineages to an extent. The Italian Barbel (Barbus plebejus) has also been introduced to the majority of rivers within the Horse Barbel's range, and hybridisation between the two species is known to have occurred at some locations.

A number of other non-native fish species that are documented to exert negative effects on native ichthyofauna through predation, resource competition or habitat degradation are also established in the region, including Pumpkinseed (Lepomis gibbosus), Largemouth Bass (Micropterus salmoides), Eurasian Perch (Perca fluviatilis), Eurasian Pikeperch (Sander lucioperca), Goldfish (Carassius auratus), Common Carp (Cyprinus domestic strain), Topmouth Gudgeon (Pseudorasbora parva), Black Bullhead (Ameiurus melas), Wels Catfish (Silurus glanis), Blue Catfish (Ictalurus furcatus), Channel Catfish (Ictalurus punctatus), Brown Trout (Salmo trutta) and Rainbow Trout (Onchorhyncus mykiss). The presence of the Ebro Barbel (Luciobarbus graellsii) at four sites along the main stem of the upper Tiber River and the Nestore tributary system is not currently considered to represent a threat, but could become problematic in the future should its distribution increase.

Additional threats identified throughout the Horse Barbel's range include construction of barriers such as dams and weirs, which interfere with discharge, water temperature and sedimentation regimes and block access to its upstream spawning grounds, water abstraction leading to reduced flows, extraction of gravel and sand from riverbeds, removal of riparian vegetation, pollution from agricultural, industrial and urban sources and canalisation of natural channels. A combination of these factors is believed to have driven an initial decline in native barbel subpopulations, which may have partially facilitated the establishment of non-native species.

Extended periods of drought due to increasingly rapid climate change in the Italian Peninsula is markedly reducing the extent of available refugia during low-discharge periods. This is particularly evident in the Tiber River system, where the upper reaches of some tributaries which are inhabited by non-introgressed Horse Barbel subpopulations are often completely dewatered by early summer.

This species is sometimes targeted by recreational anglers, but is not otherwise used or traded.

This species is included (as Barbus spp.) in Annex V of the European Union Habitats Directive, and was assessed as Endangered in the latest (2022) Red List of Italian Vertebrates.

It occurs within the boundaries of numerous protected areas, including the Foreste Casentinesi, Monte Falterona and Campigna National Park, plus a number of sites incorporated in the European Union's Natura 2000 network.

No species-specific conservation measures are known to be in place anywhere within its range.

Future conservation and research efforts should ideally prioritise a revision of freshwater fish stocking and translocation practices, alongside management measures aimed towards the identification and preservation of locations inhabited by genetically-intact Horse Barbel subpopulations. In some cases, this may mean that existing artificial barriers should be left in place in order to prevent the further expansion of non-native species.