A geographically-isolated rudd subpopulation inhabiting Lake Vrana on the island of Cres, Croatia, has in the past been treated as conspecific with the Dalmatian Rudd, but is morphologically divergent from mainland subpopulations (Sabolić et al. 2021). It is omitted from this assessment, pending confirmation of its taxonomic status.

Global and European regional assessment: Near Threatened (NT)
EU 27 regional assessment: Near Threatened (NT)

The Dalmatian Rudd has a restricted range (extent of occurrence (EOO) c. 7,451 km², EU 27 member states 5,145 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 it is not understood to be severely fragmented, the number of locations is unknown, and there is no evidence that it demonstrates extreme fluctuations. Therefore, this species is assessed as Near Threatened because it is close to qualifying for Vulnerable under Criterion B, both globally and for the EU 27 member states.

This species is endemic to the Dinaric Karst region in the Western Balkans. It occurs in the Krka and Cetina river systems in Dalmatian Zagora, Croatia, and Livanjsko polje in Bosnia and Herzegovina, which is naturally connected to the Cetina via subsurface karstic conduits.

A somewhat isolated subpopulation inhabits Lake Vrana (which confusingly shares its name with a second lake located on the island of Cres; see 'Taxonomic Notes'), located northwest of the Krka estuary.

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

This species naturally inhabits spring-fed karstic river systems, lakes and associated temporal wetlands characterised by complex surface-groundwater hydrological interactions and seasonal fluctuations in discharge. It demonstrates a preference for lentic conditions, and often occurs in areas with dense aquatic vegetation. Field observations indicate that it is somewhat eurytopic and able to withstand a relatively wide range of water temperatures, oxygen concentrations and salinities, although it may be sensitive to increasing nutrient loads. It has colonised some artificial systems, for example the Buško Blato accumulation lake and Ždralovački Canal in Livanjsko polje, and the Peruča accumulation lake in the upper Cetina River.

While most of its natural habitats consist of perennial river reaches and fluvial lakes, Livanjsko is an isolated karstic polje comprising a depressed flat plain enclosed by limestone ridges. A number of intermittent sinking rivers and springs rise around its borders and flow above ground for short distances before submerging into ponors. Much of this water subsequently resurfaces at the source of the Ruda River, which is the main tributary of the Cetina River. Under natural conditions, much of the polje would be flooded between early winter and early summer each year, but this process has been partially impeded  (see 'Threats').

Lake Vrana occupies a shallow (average depth 2-2.5 m, maximum depth 6 m) cryptodepression located in the coastal Vransko polje, and is the largest freshwater lake in Croatia. It is mostly recharged by groundwater and karstic springs located along its northern edge, and the water level is prone to seasonal fluctuations (average surface area c. 31 km²). During wet periods of the year its surface is higher than sea level and freshwater flows out of the system, whereas under drought conditions seawater naturally enters the lake through brackish springs on its southeastern shores. It has become increasingly saline due to engineering works carried out over the past few centuries (see 'Threats').

This species' biology and ecology have not been extensively studied. It is understood to be an omnivorous generalist in terms of diet, feeding on a variety of planktonic and benthic invertebrates, higher plant material and insects taken at the water surface.

Adult individuals reportedly mature at age 3-4+, and the annual reproductive period extends from spring to early summer. It is a fractional, polygamous spawner, and the eggs are deposited among submerged vegetation.

Although field observations suggest that this species may be resistant to moderate levels of habitat degradation (see 'Habitat and Ecology'), it is nevertheless plausibly 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.

Elsewhere, the Cetina River has been extensively 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.

While most of the Krka River system is relatively well-preserved, its upper reaches are impacted by point-source pollution from the town of Knin, where insufficiently-treated domestic wastewater is discharged directly into the river's main stem. Contaminants from local industry are also released into artificial pools along its right bank and may enter the river through the surrounding karst, or via overspill when water levels are high. A trout farm upstream of Knin represents a localised source of organic pollution since it utilises a flow-through system exploiting the river's water.

In the lower Krka catchment, the source spring of the affluent Čikola River is exploited for drinking water, and its floodplain is intensively-cultivated east of the town of Drniš, where water abstraction via a network of ditches, sluice gates, small weirs, tunnels, pipelines and groundwater extraction sites has decreased the output of some tributaries and significantly reduced the extent of ephemeral wetlands. Moreover, diffuse and point source agricultural and domestic pollution is understood to be contaminating the river downstream of this area.

Lake Vrana is directly connected to the Adriatic Sea via an artificial canal constructed during the late 18^th century in order to regulate its water level and reclaim land for agriculture. The intrusion of seawater during drought periods has since increased significantly due to the canal being enlarged on several occasions, combined with the abstraction of water from inflowing springs disrupting the lake's capacity for freshwater recharge. The northwestern part of Vrankso polje is intensively-cultivated, and the associated network of drainage channels represents a major source of increased nutrient input to the lake. The increasing prevalence of droughts driven by climate change is expected to further impact the hydrological regime of the lake, and could plausibly threaten its long-term stability.

Non-native fish species established within the Dalmatian Rudd's range include Northern Pike (Esox lucius), 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, resource competition or transmission of pathogens.

This species is not used or traded.

In Croatia, part of this species' range overlaps with the boundaries of Krka National Park, and it is present in a number of protected areas which are included in the European Union's Natura 2000 network, e.g., Krka National Park (site HR2000918), Čikola River (site HR2000919), Lake Vrana (site HR5000025), middle Cetina River (site HR2001313). Livanjsko polje and Lake Vrana are listed in The Ramsar Convention on Wetlands of International Importance (sites 1786 and 2109, respectively).

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.