Global and European regional assessment: Endangered (EN)
EU 27 regional assessment: Endangered (EN)

The Illyrian Spined Loach is endemic to the Trebižat River catchment in the Dinaric Karst system of Croatia and Bosnia and Herzegovina. It has a restricted range (extent of occurrence (EOO) c. 1072 km², EU 27 Member States 758 km²), which meets the threshold for the Endangered category under Criterion B1 (EOO < 5,000 km²). It occurs at three locations where the quality of habitat is estimated to be declining due to a range of threats which include pollution and the construction of dams. Therefore, this species is assessed as Endangered under Criterion B (B1ab(iii)), both globally and for the EU 27 Member States.

This species is endemic to the Trebižat River catchment in the Dinaric Karst system of Croatia and Bosnia and Herzegovina. The Trebižat is a sinking river that goes by several different names along its course, and is a right-bank tributary of the lower Neretva River.

The Trebižat rises from a spring in the western part of the transboundary Imotsko polje, Croatia, where it is named Vrljika until its confluence with a tributary at the village of Kamenmost. After this point it is known as the Matica until it submerges underground at the southeastern extremity of the polje in Bosnia and Herzegovina, emerging c. 1.5 km further east as the Tihaljina River, which is subsequently referred to as the Mlade and eventually the Trebižat once it enters Ljubuško polje near the village of Otok. As the Trebižat flows through Ljubuško polje, some of its water drains southward towards Vrgorsko polje, to which it is connected via subsurface karstic conduits. This water represents the main source of the short Vrgorska Matica River, which flows through Vrgorsko polje for c. 15 km before terminating in an extensive wetland.

The Illyrian Spined Loach is present throughout Imotsko polje plus a series of surrounding wetlands and sinkhole lakes comprising Prološko Blato (Prološko swamp) and Lake Crveno in Croatia, and Lake Krenica in Bosnia and Herzegovina. It also occurs in the Vrgorska Matica River and the Baćina Lakes close to the Neretva River delta, which are linked to Vrgorsko polje via a man-made tunnel.

The number of threat-defined locations is currently unclear. This species may plausibly occur elsewhere in Imotsko polje, where there exist several other sinkhole lakes, and further downstream in the Tihaljina/Mlade section of the Trebižat River.

This species' current population size and trend have not been quantified.

The Trebižat is a karstic river system of which several stretches, including the entirety of the Vrljika/Matica and Vrgorska Matica, flow through polje, i.e., depressed flat plains surrounded by limestone ridges. Under natural conditions, these areas are partially inundated from late winter to early summer due to increased river discharge in addition to rising groundwater entering through estavelles and/or ponors located around their margins.

This small, benthic species inhabits karstic streams, rivers and lakes located in and around the polje. It is typically associated with substrata of soft silt or sand and often submerged vegetation. It utilises ponors to access subterranean waterbodies and has been recorded at a depth of c. 250 metres in Lake Crveno. Like other Cobitis species, it feeds by filtering mouthfuls of fine material through the gills, from which minute organic particles and small benthic organisms are extracted and consumed. It is also a facultative air-breather that makes use of its hindgut as an accessory air-breathing organ.

Little is known of its life history, but related species tend to spawn among submerged vegetation, where the eggs are retained until they hatch.

This species is plausibly threatened by a range of anthropogenic factors. For example, the construction of accumulation dams on the affluent Ričice River has interfered with the complex natural hydrology of the Imotsko area while reducing downstream discharge in the Trebižat River, with water now redirected from the Ričice to Prološko Blato via an artificial canal.

The water level at Prološko Blato itself is partially controlled by a retention dam and canal system, and a number of stretches of the Trebižat (including its source spring in Imotsko polje) have been canalised and/or receive diffuse and point-source agricultural and domestic pollution. Most of the water draining from Imotsko polje to the Tihaljina River first accumulates in an artificial lake before passing through a tunnel and hydroelectricity plant instead of the natural ponor. Vrgorsko polje is almost entirely turned over to agriculture and the Vrgorska Matica River is extensively impacted by eutrophication and water abstraction.

All polje within its range have been at least partly modified to reduce the extent of annual flooding and provide reclaimed land for agriculture, which has significantly reduced the extent of temporal wetlands.

The increasing frequency of drought periods driven by climate change is likely to be exacerbating several of these threats.

Non-native fish taxa established within this species' range include Pumpkinseed (Lepomis gibbosus), Largemouth Bass (Micropterus salmoides), Northern Pike (Esox lucius), Eurasian Perch (Perca fluviatilis), Eurasian Pikeperch (Sander lucioperca) and Common Carp (Cyprinus domestic strain), all of which are documented to adversely affect native fish abundance through resource competition, habitat degradation and/or predation of various life stages.

This species is not used or traded.

This species is included (originally as Cobitis taenia) in Appendix III of the Bern Convention and Annex II of the European Union Habitats Directive. It is nationally protected in Croatia.

There are no specific conservation management actions in place, but in Croatia it occurs within the boundaries of two protected areas included in the European Union's Natura 2000 network.

Three genetically distinct subpopulations have been identified, and should be treated as individual conservation units.

Research investigating this species' population trend, life history and response to the identified threats would prove useful should direct managemernt actions be deemed necessary in the future.