The Channel Minnow (Phoxinus phoxinus), formerly Common or Eurasian Minnow, was for a considerable period of time treated as the only European member of the genus Phoxinus. However, at least 23 distinct mitochondrial lineages and 14 valid species have been identified in the region since the mid-2000s. This diversity is likely to increase further, as comprehensive information for all major European river systems has not yet been compiled. Moreover, additional sampling plus morphological analyses are required to corroborate some putative species divisions which are currently supported only by inconclusive nuclear data (Denys et al. 2020, Palandačić et al. 2017, 2020, 2022, Bogutskaya et al. 2023).

Taxonomic determination has been further hampered by natural phenotypic variability within the different lineages, plus their disparate geographic distributions which do not generally reflect patterns observed in related European fish genera. Furthermore, anthropogenic translocations linked to recreational fisheries have in some cases led to uncertainty regarding native range boundaries and driven introgressive hybridisation between congeners (Museth et al. 2007, Knebelsberger et al. 2015, Miró and Ventura 2015, Ramler et al. 2017, Vucić et al. 2018, Corral-Lou et al. 2019, Palandačić et al. 2020, 2022, De Santis et al. 2021).

As a result of the increasing species diversity, much of the published literature referring to Phoxinus phoxinus in fact pertains to other taxa and should therefore be reviewed with due care.

European regional assessment: Near Threatened (NT)
EU 27 regional assessment: Not Recorded

The Karst Minnow has a restricted range (extent of occurrence (EOO) c. 15,545 km²), which meets the threshold for the Vulnerable category under Criterion B1 (EOO < 20,000 km²). The extent and quality of habitat are estimated to be declining, but the number of locations is unknown, and it is unclear whether the extant subpopulations are severely fragmented or demonstrate extreme fluctuations. Therefore, this species is assessed as Near Threatened, because it is close to qualifying for Vulnerable under Criterion B.

This species is endemic to the southeastern part of the Dinaric Karst region in the Western Balkans.

In Montenegro it occurs in the Tara River (upper Drina River, Danube River system) plus the Lake Skadar (sq. Liqeni i Shkodrës; cnr. Skadarsko jezero) basin. Its range probably extends a short distance into Albania in the Skadar catchment, where the majority of records pertain to the Crnojevića and Morača tributary systems, including the Zeta and Cijevna (sq. Cem) rivers in the latter. It is also present in Nikšić polje in the upper Zeta basin.

Its native status in Bosnia and Herzegovina is somewhat uncertain, but it is present in Gatačko (Mušnica River) and Popovo poljes in the Trebišnjica River system, and Nevesinjsko polje (Zalomka River) in the Neretva River system. It co-occurs with an unidentified congener in the Mušnica and Zalomka rivers (see 'Population'), and a second unidentified lineage has been reported from the Drina River close to the city of Foča.

The precise extent of its distribution in some of these areas, e.g., the upper Drina River, has not yet been clarified.

This species' current population size and trend have not been quantified, and the number of subpopulations is unknown.

There exist a series of plausible threats which may have driven an overall decline since the mid-20^th century (see 'Threats'), but field observations indicate that it remains abundant at some locations, e.g., Popovo polje, Nikšić polje, lower Zeta River.

Introgressive hybridisation with a Phoxinus lineage of uncertain taxonomic status, which has a wider distribution in the Neretva River system and central portion of the Dinaric Karst, has been detected in the Mušnica and Zalomka river subpopulations. It is not yet clear whether this is reflective of anthropogenic translocation or natural migration of individuals through subterranean waterbodies (see 'Habitat and Ecology').

In the western part of its range and the upper Zeta River catchment, this small-bodied, gregarious species is restricted to a series of karstic poljes, each of which comprises a depressed flat plain surrounded by limestone ridges. Intermittent sinking rivers and springs rise around the boundaries of these isolated basins and flow across their floors, before submerging into ponors where they travel though subsurface karstic conduits and emerge to join rivers at lower altitudes. For example, Gatačko polje is located in the upper Trebišnjica River catchment, Nevesinjsko polje drains towards the Buna River (a short left-bank tributary of the Neretva River) and Nikšić polje is traversed by the upper course of the Zeta River. The Trebišnjica itself was the longest sinking river in Europe prior to modification and its lower course cuts across the extensive Popovo polje, from where it mostly discharges into ponors draining to the Ombla Spring near Dubrovnik, Croatia. However, some of its water flows underground to Čapljina Spring in the Hutovo Blato wetland basin, and the river is therefore often regarded as belonging to the Neretva catchment.

Under natural conditions, parts of these poljes would be inundated and form a temporal wetland between early winter and early summer each year, but this process has been largely restricted within the Karst Minnow's range (see 'Threats'). Field observations indicate that it occurs in perennial spring outflows and sinkhole ponds, and some individuals are understood to enter subterranean water bodies through estavelles and ponors. It is also abundant in some canalised river stretches and artificial accumulation lakes, e.g., Bilećko and Goričko reservoirs in the Trebišnjica system.

The Tara and Morača rivers are perennial systems draining a rugged mountainous area. The majority of their courses pass though steep-sided valleys and are punctuated by stretches of whitewater, although the Zeta River (Morača system) mostly flows through the lowland Bjelopavlići Plain. The Crnojevića is a slow-moving river which emerges from a cave and flows for just a few kilometres before emptying directly into Lake Skadar. This species has been recorded throughout these systems, and in upland reaches reportedly demonstrates a preference for relatively shallow pools and glides with well-oxygenated, clear water and slow to moderate water movement. There also exist numerous records from Lake Skadar itself, particularly in areas influenced by sublacustrine (underwater) springs.
 
It mostly feeds on aquatic invertebrates, supplemented by smaller quantities of organic detritus and plant material.

Adult individuals reach sexual maturity at age 1-3+, and the annual reproductive period extends from March to June. This species is a fractional, polygamous spawner, and older individuals tend to spawn earlier in the season. Spawning behaviour is characterised by mature adults migrating short distances to specific sites, usually comprising beds of aquatic vegetation or well-washed gravel. Reproductive males develop a conspicuous epigamic colour pattern, and often aggregate in the vicinity of spawning sites prior to the arrival of females. Epidermal breeding tubercles appear on the head in both sexes, but are more prominent in males.

This species is plausibly threatened by river regulation and other forms of anthropogenic habitat degradation throughout its range.

For example, the hydrological regime of Gatačko polje has been significantly disrupted due to construction of two accumulation dams in its upper reaches. In addition, the northwestern part of the polje has been extensively degraded since the 1970s following construction of a coal-fired power plant and open-pit mining operation. Water is directed through a pipeline from the two reservoirs to supply the power plant, and no longer flows through the polje. A number of the Mušnica River's tributaries have been channelised in order to prevent flooding in the area around the mine, and the lower reaches of the Mušnica main stem are also regulated.

Future proposals involve the channelling and pumping of water from the Mušnica River to Nevesinjsko polje within the framework of the "Upper Horizons" hydropower strategy. This scheme aims to artificially redirect water from several poljes to the Bileća accumulation lake in the Trebišnjica River system through a cascading series of canals, tunnels and small hydroelectric power stations. As of mid-2023, an artificial storage reservoir and tunnel were under construction on the lower Zalomka River in Nevesinjsko polje, and will be used to route water towards the Trebišnjica (and therefore away from the lower Neretva River) via the nearby Dabarsko polje. The potential impact of these engineering works on native fishes has not been studied in detail, but the extent of seasonal flooding is likely to be reduced while some key springs and ponors in Nevesinjsko polje could be inundated by the new reservoir.

The Trebišnjica River system has already been heavily modified by the "Lower Horizons" hydropower scheme, which was initiated during the 1960s and today comprises several dams and hydroelectric plants. The artificial lakes associated with these barriers have favoured the widespread establishment of non-native fish species (see below). Since 1978 much of the main stem has been converted into a 65-kilometre canal designed to prevent loss of water into the surrounding karst, and former temporal wetlands at some locations, e.g., Popovo polje, no longer exist. Non-native fish species introduced to the Trebišnjica system include Pumpkinseed (Lepomis gibbosus), Eastern Mosquitofish (Gambusia holbrooki), Common Carp (Cyprinus domestic strain), Prussian Carp (Carassius gibelio), Topmouth Gudgeon (Pseudorasbora parva), Wels Catfish (Silurus glanis), and Rainbow Trout (Oncorhynchus mykiss), all of which are considered invasive and can exert detrimental pressures on native freshwater fauna through increased competition, predation or habitat degradation. A number of species have also been introduced to the Bileća lake for aquaculture or recreational fisheries purposes.

The hydrological regime of the upper Zeta River in Nikšić polje has been extensively modified since the late 1950s in order to facilitate operation of a large hydropower plant. Accumulation dams have been constructed on each of the river's three main tributaries, and their discharge is regulated through artificial canals. The third tributary is polluted by runoff from a series of bauxite mines located within its catchment. The lowermost kilometres of the upper Zeta itself have also been converted into a canal, and its water is directed into an intake structure before being transported to the hydropower plant via a tunnel and pipeline system. The canalised section of the river is polluted due to widespread disposal of household garbage and other waste. The ponor into which the upper Zeta formerly submerged has been isolated by a circular dam and no longer receives water, while seasonal flooding in the polje has been significantly reduced.

Native fish declines in Lake Skadar have been ongoing since the mid-20^th century. The lower reaches of the Morača River system are polluted due to long-term discharge of agricultural and industrial contaminants plus municipal wastewater from Nikšić polje, the city of Podgorica and other communities. As a result, the naturally oligotrophic lake has become increasingly eutrophic, leading to structural changes in the resident planktonic and zoobenthic communities and thus the overall food chain. A number of non-native fish species have been introduced to the basin, including Goldfish (Carassius auratus), Grass Carp (Ctenopharyngodon idella), Eurasian Tench (Tinca tinca), Eurasian Perch (Perca fluviatilis), Eurasian Pikeperch (Sander lucioperca), Northern Pike (Esox lucius), Pumpkinseed, Brown Bullhead (Ameiurus nebulosus) and Rainbow Trout.

At some locations restocking with hatchery-reared Brown Trout (Salmo trutta) or related species may represent a threat due to the risk of over-predation or the transmission of non-native diseases or parasites.

This species is not used or traded.

The Montenegrin part of Lake Skadar was designated a National Park in 1983 and a Ramsar Wetland of International Importance in 1995, while the Albanian portion was nationally-protected and added to the Ramsar Convention in 2005. The lower Zeta River catchment in Montenegro has been a protected area since 2019.

In Bosnia and Herzegovina, Gatačko and Nevesinjsko poljes have both been identified as candidate Emerald Network areas of special conservation interest but are not currently protected.

A deeper understanding of this species' present distribution, demographics (population size and trend), life history and response to the ongoing threats would likely prove beneficial in the design of any structured management plan.