The Catalan Chub 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, and hence does not meet the thresholds for Criteria C or D. There exists no quantitative analysis which would permit application of Criterion E.

Although no explicit population trend data exists, it is suspected that an ongoing reduction based on declining habitat quality and the effects of introduced taxa may approach or meet the thresholds for Vulnerable or Endangered under Criterion A (≥ 30% or ≥ 50% over the past 15 years = three generations).

As a result of this data uncertainty, Near Threatened and Endangered are equally plausible Red List categories for the present assessment, therefore this species is assessed as Vulnerable.

This species' native range extends southward from the Agly River system in southeastern France to the Ebro (ca. Ebre) River system in northeastern Spain. It is naturally restricted to the lower part of the Ebro catchment, where it is most abundant in the Matarraña (ca. Matarranya) and Segre tributary systems.

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, but an ongoing reduction which may have exceeded 30% within the past three generations is suspected as a result of a continued decline in habitat quality. The number of subpopulations is unclear.

Significant declines documented throughout its range since the mid-1980s have been attributed to declining habitat quality and the effects of introduced taxa, and this pattern is suspected to be ongoing to an as yet undetermined extent (see 'Threats'). In France, it is currently restricted to small, isolated parts of the Agly River and headwaters of the Têt and Tech river systems, and field observations suggest that it is becoming similarly scarce in Spain (I. Doadrio, pers. comm.).

The Catalan Chub is considered to be a eurytopic generalist since it can be found throughout its native river systems, from larger lowland channels to headwater streams. However, it tends to be most abundant in the middle reaches of medium-sized river channels with clear water, moderate flow, well-developed riparian vegetation and rocky to stony substrata, e.g., mixed bedrock, gravel and pebbles. Adult individuals demonstrate a preference for deeper glides and pools.

Many of its habitats in Spain are characterised by seasonal variations in discharge, and can be significantly dewatered during summer. Some individuals survive these drought periods in remnant pools which function as refugia. It is able to survive in eutrophic conditions, albeit with reduced reproductive success, and has also colonised some artificial accumulation lakes at locations where there is access to suitable upstream spawning habitat (but see 'Threats').

This species feeds largely on invertebrates, but also consumes detritus and smaller fishes.

The maximum recorded lifespan is c. 12 years. In Spain, male individuals become sexually mature at age 2+ and females age 3+, whereas in France both sexes mature at age 2+ and a small number at age 1+. The annual reproductive period extends from March to July, with the precise timing dependant on location and environmental conditions such as water temperature. It is characterised by the upstream migration of mature adults to spawning sites comprising beds of gravel or other coarse substrata in shallow, flowing water.

The most immediate threat is insidious expansion of the non-native European Chub (Squalius cephalus) within this species' range, which is driving widespread introgressive hybridisation in France and Catalonia, Spain. Subpopulations inhabiting some watersheds, e.g., the Massane River, France, may already consist entirely of hybrids.

Other non-native fish species established within the Catalan Chub's range include Common Carp (Cyprinus domestic strain), Common Roach (Rutilus rutilus), Northern Pike (Esox lucius), Eurasian Perch (Perca fluviatilis), Largemouth Bass (Micropterus salmoides), Pumpkinseed (Lepomis gibbosus) and Topmouth Gudgeon (Pseudorasbora parva), 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 (see below) since they broadly prefer lentic conditions.

This species' decline is also understood to have been driven by river regulation and other forms of anthropogenic habitat degradation, which have resulted in widespread loss of the heterogeneous, interconnected fluvial habitats required to complete its life-cycle. The construction of large dams plus smaller weirs and other barriers throughout its range has severely altered natural flow and sedimentation regimes, blocked migration routes, fragmented subpopulations, and reduced the extent of suitable habitat for all life stages. Hydroelectric dams have created unnatural fluctuations in discharge and water temperature (hydropeaking and thermopeaking) which bring about artificial dewatering of downstream river stretches and loss of stable nursery habitat for juveniles. Furthermore, the combined effect of hydropeaking, dam flushing operations, changes in land use, and the removal of riparian vegetation has increased accumulation of fine sediments at some spawning sites, plausibly impairing the hatching and survival rates of eggs and larvae.

The quality of available habitat has been further diminished by bank stabilisation, channelisation and other efforts to enhance flood protection or exploit water resources for irrigated agriculture. Unregulated water abstraction may constitute a particular threat to this species' upstream spawning and nursery sites, some of which may also have been damaged by the industrial extraction of riverine gravel for urban development.

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').

The negative impact of some threats could plausibly be exacerbated by increasingly rapid climate change, which is already driving extended periods of drought in the Mediterranean region. Some areas in the Spanish region of Catalonia received no rainfall at all between 2020-2023, leading to an extended period of significantly decreased river discharge throughout the southern part of this species' range.

This species is occasionally targeted by recreational anglers, but is not otherwise used or traded.

This species is included in Appendix III of the Bern Convention (as Leuciscus pyrenaicus).

In Spain, it has been recommended for inclusion in the Spanish Catalogue of Threatened Species, while in France it was assessed as Endangered for the most recent (2019) iteration of the National Red List.

It occurs within the boundaries of various protected areas throughout its range, including a number of national parks and sites included in the European Union's Natura 2000 network.

Some subpopulations in Spain may have benefitted from improvements in water quality associated with implementation of the European Union The Water Framework Directive 2000/60/EC, plus an increasing tendency to install or improve the efficiency of fishways on existing barriers within its range.

A deeper understanding of this species' demographics (population size and trend), current distribution and life history would likely prove useful in the development of future management efforts. Locations where non-hybrid subpopulations remain should ideally be identified and prioritised for conservation actions.