This taxon is often referred to as the "Squalius alburnoides complex" due to its intricate reproductive dynamics and hybrid origin (see 'Habitat and Ecology'). Its placement in the genus Squalius has not been unequivocally confirmed, but is generally accepted by recent authors (Collares‐Pereira et al. 1999, Collares‐Pereira and Coelho 2010, Doadrio et al. 2011, Magalhães et al. 2023).

Although this species' population trend might be decreasing due to habitat degradation, the rate of decline is not understood to approach 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 B (extent of occurrence (EOO) < 20,000 km², area of occupancy (AOO) < 2,000 km²) or D2. The population size is believed to significantly exceed 10,000 mature individuals, hence it does not approach the thresholds for Criteria C or D. There exists no quantitative analysis which would permit application of Criterion E.

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

This species is widely distributed in Atlantic river systems draining the western Iberian Peninsula, where its range extends southward from the Douro (es. Duero) River to the Guadalquivir River.

It has been introduced to the Guadalhorce and Júcar river systems in Spain, both of which drain to the Mediterranean Sea.

This species' population size is unknown, but is understood to significantly 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.

This species tends to be absent from large and deep lowland rivers, but is otherwise considered to be a habitat generalist since it occurs in rivers and streams at different altitudes and with a diverse range of flow regimes.

Many of its habitats 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 an opportunistic omnivore feeding predominantly on aquatic invertebrates, supplemented by smaller quantities of terrestrial insects, detritus and plant material. There is evidence of partial habitat and resource partitioning between the different genomotypes (see below for definition).

The annual reproductive period extends from March to June, with the precise timing dependant on location and environmental conditions such as water temperature. It is a fractional spawner, and nuptial male individuals develop numerous small tubercles on the head and body.

This species' reproductive dynamics have been the focus of extensive research. It comprises an allopolyploid complex descended from unidirectional hybridisation between female individuals of the Southern Iberian Chub (Squalius pyrenaicus) and males of an extinct species related to the extant Iberian Minnowcarp (Anaecypris hispanica). Contemporary subpopulations occur in reproductive sympatry with different bisexual Squalius species, which contribute new genetic material and thus facilitate gene flow and the continuous cycling of genomes between the resulting assortment of diploid, triploid and tetraploid forms. The genomic constitution (genomotype) of these forms is characterised by distinct combinations of the parental genomes, which differ depending on geographic location. Sex ratios also vary among genomotypes and locations, e.g., triploid individuals are mostly female, whereas diploids are mostly male in northern subpopulations but mostly female in southern subpopulations. All known forms are fertile and employ a range of asexual and sexual reproductive modes ranging from regular (sexual) meiosis to meiotic hybridogenesis, and more rarely gynogenesis and the first recorded case of androgenesis in a vertebrate. In the southern part of the range, a small-bodied, almost exclusively male form referred to as ‘nuclear non-hybrid’ occurs and contributes significantly to the maintenance of local genetic diversity. This is exemplified by the subpopulation inhabiting the Mondego River system in Portugal, where genetic diversity is comparatively low due to an absence of nuclear non-hybrid and tetraploid individuals.

This species is plausibly threatened by diffuse and point source pollution from agricultural, domestic and industrial sources, eutrophication, construction of dams and weirs, canalisation of river channels, removal of riparian vegetation and other forms of habitat modification.

A number of non-native fish species known to exert negative effects on native taxa through hybridisation, predation, resource competition or transmission of pathogens are established within its range. These include Common Carp (Cyprinus domestic strain), Largemouth Bass (Micropterus salmoides), Pumpkinseed (Lepomis gibbosus) and Topmouth Gudgeon (Pseudorasbora parva).

The ongoing spread of non-native Common Bleak (Alburnus alburnus) in the Iberian Peninsula is understood to represent a particular threat, since it is hybridising with a number of native Squalius species in different river systems, and may be interfering with the complex reproductive dynamics of the S. alburnoides complex.

Although not a threat in itself, it is noteworthy that the persistence of the S. alburnoides complex is entirely dependant on presence of the sympatric bisexual Squalius species, which is required for the production of diploid individuals. These taxa are widely threatened throughout its range.

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 Iberian Peninsula.

This species is not used or traded.

This species is included (as Rutilus alburnoides) in Appendix III of the Bern Convention and Annex II of the European Union Habitats Directive.

It was assessed as Vulnerable in the Atlas and Red Book of the Freshwater Fishes of Spain (2002) and Least Concern in the Portugese Red Book of Freshwater and Diadromous Fishes (2023).

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. It is listed as a target species in some of the latter.

A deeper understanding of this species' population trend and current distribution would likely prove useful in the development of future management efforts. Given the extent of its range, such efforts may be best coordinated at local or regional scales.