Global and European regional assessment: Least Concern (LC)
EU 27 regional assessment: Least Concern (LC)

Although this species' population trend may be decreasing due to habitat degradation, there is no evidence that the rate of decline approaches the minimum threshold for Vulnerable under Criterion A (≥ 30% over the longer of 10 years or three generations). It 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, hence it does not meet the thresholds for Criteria C or D. There exists no quantitative analysis which would permit application of Criterion E.

Therefore, the Thracian Chub does not currently meet the thresholds for any Red List criteria, and it is assessed as Least Concern.

This species is native to the northern Aegean Sea basin, where its range extends eastward from the Mygdonia drainage basin, which includes lakes Volvi (el. Βόλβη) and Koroneia (el. Κορώνεια), to the transboundary Struma (el. Στρυμόνας; bg. Струма), Nestos (el. Νέστος; bg. Места) and Maritsa (el. Έβρος; bg. Марица; tr. Meriç) river systems. It has also been reported from three minor rivers in the Republic of Türkiye, which drain to the Gulf of Saros, Dardanelles Strait and northwestern Sea of Marmara, respectively.

A putatively introduced subpopulation is present on the Greek island of Thasos (el. Θάσος).

This species' population size is unknown, but is likely to exceed the minimum threshold for Red List criteria (< 10,000 mature individuals). The current population trend has not been quantified, and the number of subpopulations is unclear.

Field observations indicate that it remains abundant where favourable habitat conditions exist, e.g., in parts of the Nestos River and some tributaries of the upper Maritsa system, but may have been extirpated from some locations, e.g., the Vacha River, Bulgaria.

This species is considered to be a eurytopic generalist since it can be found throughout its native river systems, from larger lowland channels to headwater streams. It tends to be most abundant in reaches with moderate flow, but also inhabits some fluvial lakes provided there is access to suitable spawning sites in affluent rivers or streams.

Some of its habitats are characterised by seasonal variations in discharge, and can be significantly dewatered during summer. Many individuals survive these drought periods in remnant pools which function as refugia. It is able to survive in eutrophic conditions, and has colonised some artificial accumulation lakes.

It feeds largely on invertebrates, but also consumes organic detritus, plant material and smaller fishes.

Adult individuals become sexually mature at age 1-2+, and the the annual reproductive period extends from spring to early summer. It is characterised by the upstream migration of mature adults to spawning sites comprising beds of gravel or other coarse substrata in shallow, fast-flowing water.

This species is plausibly threatened by river regulation and other forms of anthropogenic habitat degradation. The construction of large dams plus smaller weirs and other barriers throughout its range has severely altered natural flow and sedimentation regimes, fragmented subpopulations, and reduced the extent of habitat for all life stages of native fish species. Hydroelectric dams have created unnatural fluctuations in discharge and water temperature (hydropeaking and thermopeaking) which bring about artificial dewatering of downstream river stretches.

The quality of habitat has been further diminished by bank stabilisation, channelisation, removal of riparian vegetation and other efforts to enhance flood protection or exploit water resources for irrigated agriculture. Unregulated water abstraction may constitute a particular threat in temporal river channels. Some locations may also have been damaged by the industrial extraction of riverine gravel or sand for urban development.

The Mygdonia basin has experienced a well-documented period of intense ecological degradation since the mid-20^th century. The water level of lake Volvi is slowly decreasing due to abstraction of water for irrigated agriculture, which accounts for c. 95% of all local water demand. The Mygdonia aquifer is suffering from limited recharge, and excessive pumping has caused the groundwater table to subside. The partial diversion of two temporal tributary streams into Lake Koroneia has decreased the volume of runoff entering Lake Volvi. Recent climate models for the Mygdonia basin suggest that rainfall is set to decrease by 17%, surface runoff by 21% and groundwater recharge by 38% before 2100, with Lake Volvi potentially losing almost half of its current surface area. Lake Koroneia has almost dried out on several occasions with at least two instances of food web collapse leading to major kills of resident fishes.

This species is also threatened by diffuse and point source agricultural, domestic and industrial pollution, which has reduced the extent and quality of habitat at some locations due to eutrophication or discharge of toxic substances. Pollution can be particularly impactful when discharge is reduced during the summer, especially in temporal rivers where native fishes are often confined to small refugia (see 'Habitat and Ecology'). In the Mygdonia basin, the water quality of affluent rivers which presumably comprise this species' spawning sites is being degraded by point source discharge of agricultural (livestock and arable farming), domestic (wastewater) and industrial (cheese production) effluents.

Non-native species established in parts of the Thracian Chub's range include Prussian Carp (Carassius gibelio), Pumpkinseed (Lepomis gibbosus), Largemouth Bass (Micropterus salmoides), Northern Pike (Esox lucius), Eurasian Perch (Perca fluviatilis), Eurasian Pikeperch (Sander lucioperca), Topmouth Gudgeon (Pseudorasbora parva), Eastern Mosquitofish (Gambusia holbrooki) and Rainbow Trout (Oncorhynchus mykiss), all of which are considered invasive and can exert detrimental pressures on native freshwater fauna through increased competition, predation, habitat degradation or transmission of pathogens. The presence of these taxa is favoured by barrier construction since they broadly prefer lentic conditions, and there is evidence to suggest that Thracian Chub abundance can be significantly reduced once they are established.

The negative impact of some threats could plausibly be exacerbated by increasingly rapid climate change in the Mediterranean region, which is already driving extended periods of drought.

This species might be harvested by commercial fishers operating on some natural and artificial lakes, but few details are available.

A sizeable proportion of this species' range lies within the boundaries of protected areas, including the National Wetland Park of Lakes Koroneia-Volvi and the Macedonian Tempe, plus a number of sites included in the European Union's Natura 2000 network in both Bulgaria and Greece.

A deeper understanding of its 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 and monitoring efforts. Given the nature of its range, such efforts may be best coordinated at separate national scales.