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

The Minnow Nase has a restricted range (extent of occurrence (EOO) c. 4,779 km²), which meets the threshold for Endangered under Criterion B1 (EOO < 5,000 km²). It occurs at five locations, and the extent and quality of habitat are estimated to be declining due to a range of threats which include dam construction, water abstraction, and pollution. Therefore, this species is assessed as Endangered under Criterion B (B1ab(iii)), both globally and for the EU 27 member states.

This species is native to the Cetina River system in the Dinaric Karst region of Dalmatian Zagora in Croatia, plus Livanjsko, Glamočko and Duvanjsko poljes in Bosnia and Herzegovina, which drain to the Cetina via subsurface karstic conduits. Elsewhere in Croatia, it occurs in the Prološko Blato wetland and its outflow in Imotsko polje, located in the upper Trebižat River (Neretva River catchment).

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

It has declined markedly in most parts of its range since the mid-20^th century, e.g., the Cetina River system, Livanjsko polje, Prološko Blato.

This gregarious species naturally inhabits spring-fed river systems, lakes and associated temporal wetlands characterised by complex surface-groundwater hydrological interactions and seasonal fluctuations in discharge.

With the exception of the Cetina River, it is largely restricted to a series of isolated karstic poljes. Each of these comprises a depressed flat plain enclosed by limestone ridges, around the borders of which rise intermittent sinking rivers and springs which flow above ground for short distances before submerging into ponors. Much of this water subsequently resurfaces in adjacent poljes or the headwaters of larger rivers. Under natural conditions, part of each polje would be inundated to form an ephemeral wetland between early winter and early summer each year, but this no longer occurs throughout much of the Minnow Nase's range (see 'Threats'). Prološko Blato is a perennial but seasonally-fluctuating wetland, and it currently drains to the upper Trebižat River via a modified channel.

Like a number of other fish species that are endemic to the Dinaric Karst region, this species utilises estavelles and ponors to enter subsurface waterbodies. This behaviour is habitual during periods of drought or cold winters, and many individuals are understood to spend considerable periods of time underground. In Livanjsko polje, it has recently been observed in a few disused lignite mining pits which have filled with water, to which it presumably arrived through such subterranean connections.

Its ecology has not been extensively-studied, but the diet is understood to comprise periphyton and benthic invertebrates.

The annual reproductive period extends from March to May, coinciding with high water levels. The eggs are apparently attached to submerged vegetation in temporarily-inundated floodplains, which also provide nursery habitat for juveniles.

This species is threatened by diffuse and point source agricultural and domestic pollution, eutrophication, construction of dams and weirs, canalisation of river channels, water abstraction and other forms of habitat modification. All poljes within its range have been modified to reduce the extent of annual flooding and provide reclaimed land for agriculture, which has altered hydrological regimes and significantly reduced the extent of spawning and nursery habitat for native fish species, while encouraging the establishment of introduced taxa (see below).

In particular, the Buško Blato accumulation lake was constructed during the 1970s in order to provide water for hydropower generation and agriculture, and has largely eliminated natural flooding processes in Livanjsko and Duvanjsko poljes. Water from Buško Blato and springs rising in other parts of Livanjsko polje is directed through a canal system to the smaller Lipsko compensation lake, which regulates discharge towards a hydroelectric power plant located at the source of the Ruda River, a major tributary of the Cetina River.

The Cetina system has been further modified for water storage and generation of hydroelectricity, with a series of power plants, dams, accumulation lakes, tunnels and pipelines constructed within the system. These engineering works have resulted in an overall reduction in discharge and interfered with sedimentation rates as well as the hydrological regime of some left-bank tributary springs. A number of springs have also been tapped for domestic water supply, thus further reducing their output. Some stretches of the main stem and springs have been channelised leading to a loss in habitat heterogeneity. The middle reaches of the Cetina pass through Sinjsko polje, which has mostly been reclaimed for agriculture. The river is polluted downstream of the polje, where it receives diffuse agricultural contaminants plus point source domestic and industrial pollution from the towns of Sinj and Trilj.

The construction of accumulation dams has interfered with the natural hydrology of Imotsko polje, with water today redirected from the nearby Ričice River to Prološko Blato via an artificial canal. The lake's natural flood cycle has been disrupted, and the water level is partially controlled by a retention dam and canal system which includes its major outflow.

Non-native fish species established within the Minnow Nase's range include Eurasian Pikeperch (Sander lucioperca), Pumpkinseed (Lepomis gibbosus), Common Carp (Cyprinus domestic strain), Prussian Carp (Carassius gibelio), Eurasian Tench (Tinca tinca), Topmouth Gudgeon (Pseudorasbora parva), Wels Catfish (Silurus glanis) and Rainbow Trout (Oncorhynchus mykiss), all of which are known to exert negative effects on native taxa through hybridisation, predation, transmission of pathogens or resource competition.

This species is not used or traded.

This species is included in Appendix III of the Bern Convention and Annex II of the European Union Habitats Directive.

It is nationally-protected in Croatia, where it is covered by the Nature Protection Act (OG 80/13) and Ordinance on Strictly Protected Taxa (OG 144/13, 73/16), and is strictly protected at the regional scale in the Federation of Bosnia and Herzegovina.

It is currently assessed as Endangered for the National Red List of Croatia.

It occurs within the boundaries of several protected areas, some of which are included in the European Union's Natura 2000 network (sites HR2000929, HR2000932 and HR2001313). Livanjsko polje is listed in The Ramsar Convention on Wetlands of International Importance (site no. 1786).

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