The South European Nase does not approach the range 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 10,000 mature individuals, and hence does not approach the thresholds for Criteria C or D. There exists no quantitative analysis which would permit application of Criterion E.

Although no explicit population trend data exist, it is suspected that an ongoing reduction based on field observations, declining habitat quality and the effects of introduced taxa may approach or meet the thresholds for Vulnerable or Endangered under Criterion A (≥ 30% or ≥ 50% over the past 15 years = three generations). As a result of this data uncertainty, Near Threatened and Endangered are equally plausible Red List categories for the present assessment, therefore this species is assessed as Vulnerable.

This species is native to the northern Adriatic Sea basin, where its range extends from the Vomano River in eastern Italy to the Soča (it. Isonzo) River in western Slovenia. The precise limits of its current distribution are somewhat unclear, since some areas have not been exhaustively sampled and previously unreported sites continue to be discovered.

Since the 1960s, it has been widely-introduced to rivers draining the Ligurian and Tyrrhenian slopes of western Italy. For example, in Umbria region, it is present in the middle and upper reaches of the Tiber River and the lower parts of its major tributaries such as the Chiascio-Topino, Paglia, Nera and Nestore rivers. It has also been reported from the Corbara, Alviano and Recentino accumulation lakes. In the region of Lazio, it is relatively abundant in the Fiora, Mignone and Marta rivers and is also established in the Garigliano River.

This species' population size is unknown, but is understood to exceed the minimum threshold for Red List criteria (< 10,000 mature individuals).  The current population trend has not been quantified, but an ongoing reduction which may have exceeded 30% within the past three generations is suspected as a result of a continued decline in habitat extent and quality. The number of subpopulations is unclear.

There exists clear evidence of a significant population size reduction since the mid-20^th century, particularly in lower and middle reaches of the Po River and its tributaries. Moreover, it has been largely extirpated from the Soča River system, where it may now restricted to one minor river in the Friuli Venezia Giulia region of Italy and another in the Littoral region of Slovenia. In Italy, this pattern of decline is suspected to be ongoing in the Piedmont, Lombardy, Emilia-Romagna, Veneto, Friuli-Venezia Giulia, and Abruzzo regions, based on field observations, declining habitat quality and the effects of introduced taxa (see 'Threats'). Subpopulations inhabiting some smaller river catchments in the Marche region (e.g., the Foglia, Metauro and Tenna rivers) are understood to be relatively stable, although declines have been reported in others (e.g., the Esino and Tronto rivers).

Abundance is also believed to be stable or possibly increasing throughout its non-native range in the regions of Liguria, Tuscany, Umbria and Lazio.

Overall, it is today estimated to occupy 25-60% of its original native range, and its conservation status is Unfavourable-Bad according to the latest (2013-2018) period of reporting for Article 17 of the European Union Habitats Directive.

This gregarious, potamodromous species typically inhabits the lower and middle reaches of tributary rivers and streams at altitudes of < 400 m AMSL. It is most abundant in stretches with heterogeneous habitat features comprising multiple riffles, runs, pools and glides, moderate flow, coarse stony substrata, submerged rocky or woody structures, undercut banks and well-developed riparian vegetation.

It feeds partially on periphyton which it scrapes from the surface of submerged rocks and other surfaces using specialised mouthparts, but also consumes organic detritus and benthic macroinvertebrates.

Adult individuals mature at age 3-4+ and the annual reproductive period extends from March to June, with the precise timing dependant on location and climatic conditions. Spawning behaviour is characterised by nuptial adults migrating short distances to specific upstream sites, usually comprising beds of well-washed gravel in shallow, flowing water. Reproductive male individuals develop a conspicuous epigamic colour pattern and epidermal breeding tubercles on the head. It is a fractional and polygamous spawner, and individual females may deposit 2,000-5,000 eggs per year. The incubation period is approximately 10 days, but can vary somewhat depending on water temperature.

In some Italian rivers, its introduction has been associated with reduced abundance and physical condition in the Apennine Roach (Sarmarutilus rubilio) and Italian Riffle Dace (Telestes muticellus).

This species' decline is understood to have been driven by river regulation and other forms of anthropogenic habitat degradation, which have resulted in widespread loss of the heterogeneous, interconnected fluvial habitats required to complete its life-cycle. The construction of dams, sills, weirs and other barriers throughout its range 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 has 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 for irrigated agriculture. Unregulated water abstraction may constitute a particular threat in smaller tributaries, and at some upstream spawning and nursery sites. Some habitats have also been damaged by the industrial extraction of riverine gravel and other sediments for urban development, removal of riparian vegetation and/or maintenance procedures such as dredging or the removal of fallen branches and other debris which provide both cover and surfaces on which this species grazes.

This species is further 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 discharge of toxic substances. Pollution can be particularly impactful in minor river systems when discharge is reduced during the summer.

Its decline in the Soča River is believed to have been at least partially driven by competitive interactions with the non-native Common Nase (Chondrostoma nasus), which was introduced for recreational fisheries purposes during the mid-20th century.

Other non-native fish taxa established within this species' range include Pumpkinseed (Lepomis gibbosus), Largemouth Bass (Micropterus salmoides), Eurasian Perch (Perca fluviatilis), Common Bream (Abramis brama), Common Roach (Rutilus rutilus), Common Barbel (Barbus barbus), Goldfish (Carassius auratus), Crucian Carp (Carassius carassius), Common Carp (Cyprinus domestic strain), Grass Carp (Ctenopharyngodon idella), Topmouth Gudgeon (Pseudorasbora parva), Black Bullhead (Ameiurus melas), Wels Catfish (Silurus glanis), Brown Trout (Salmo trutta) and Rainbow Trout (Onchorhyncus mykiss), all of which are considered invasive and can exert detrimental pressures on native freshwater fauna through increased competition, predation, habitat degradation or parasite transmission. Native fish species have been completely displaced by non-native communities in some parts of the Po River system.

Predation pressure from increasingly abundant piscivorous birds, particularly Great Cormorant (Phalacrocorax carbo), has also been suggested to represent a significant threat in the Po River catchment.

The negative impact of some threats could plausibly be exacerbated by increasingly rapid climate change in the northern Adriatic region, which is already driving extended periods of drought. During the summer of 2022, a severe drought in Slovenia resulted in the dewatering of some streams to which this species had been introduced within the framework of a conservation project (see 'Conservation'). As a result, numerous individuals were manually translocated to perennial downstream habitats.

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

This species is listed (as Chondrostoma genei) in Appendix III of the Bern Convention and Annex II of the European Union Habitats Directive.

It was assessed as Endangered for the most recent (2022) Red List of Italian Vertebrates.

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

This species was among the native fishes targeted by the European Union co-funded LIFE project "CON.FLU.PO." (LIFE11 NAT/IT/000188), which aimed to restore fluvial connectivity in a stretch of the Po River system, Italy. The project took place from 2012-2017 and involved a series of actions, including the installation of a fishway permitting passage around a large artificial barrier located on the Po main stem near the city of Piacenza. Ex situ reproduction and reintroduction methods were developed for several species, including the South European Nase, and these efforts were ongoing as of 2023.

It is also likely to have benefitted from the LIFE project, "LifeTicinoBiosource" (LIFE15 NAT/IT/000989), which took place in the Ticino River catchment within the Po system from 2016-2021. The primary conservation activities comprised the improvement and restoration of fluvial habitats for a range of taxa including fishes, amphibians, birds and insects.

This species was also targeted by the LIFE project "Saving Lasca" (LIFE20 NAT/SI/000644), an international collaboration which took place from 2017-2022. Within the framework of this project, an ex situ reproductive stock was established using individuals sourced from Italy. In addition, more than 130,000 captive-bred individuals were introduced to tributaries of the karstic Vipava River, a Natura 2000 site and left-bank affluent of the lower Soča River in Slovenia from which the native subpopulation was extirpated during the 2000s. In 2020, young-of-the-year individuals were observed at two sites in the Vipava system, indicating that natural reproduction had occurred. Additional conservation efforts included the removal of Common Nase individuals from the Vipava River, and an extensive series of outreach activities aimed at relevant stakeholders, particularly the angling community and youth sector, also took place. An action plan for long-term management of the Vipava River site was created, which included a series of measures designed to improve the extent and quality of habitat plus the continuation of ex situ reproduction and introduction efforts.

Earlier LIFE projects which took place in northern Italy and may have aided this species include LIFE "Taro" (LIFE98 NAT/IT/005138) and LIFE "Sorba" (LIFE09 NAT/IT/000213), while it is also included in the ongoing (2022-2027) project LIFE "Minnow" (LIFE21 NAT/IT/101074559) which aims to restore fluvial connectivity in streams of the Piedmont region.

In 2022 a new Natura 2000 site was created to specifically protect what may be the last relatively large and well-structured natural subpopulation inhabiting the Italian part of the Soča River system. Actions to physically remove Common Nase individuals from this site have since taken place.

In Central Italy, a pilot scheme involving the translocation of individuals from rivers in the species' non-native range to sites in the Esino River, which is located in the southern part of its native range, was carried out during the early 2020s. Some individuals were also transported to northern Italy where they were used to produce stock for the LIFE "Saving Lasca" project (see above).

A deeper understanding of this species' demographics (population size and trend), current distribution and life history, particularly the identification of key spawning sites, would likely prove useful in the development of future management efforts. Given the extent of its range, such efforts may be best coordinated at local or regional scales.