This taxon's systematic status is in need of clarification. It is not considered to be valid by the relevant authorities in France, and was not included in the most recent National Red List (UICN, 2019; Keith et al. 2020).

At the broader scale, there is currently no general consensus regarding the systematic classification of Eurasian and North African brown trouts, an assemblage comprising all representatives of the genus Salmo except the well-differentiated Atlantic Salmon (Salmo salar), Marble Trout (Salmo marmoratus), Softmouth Trout (Salmo obtusirostris) and Ohrid Belvica (Salmo ohridanus). While numerous, often range-restricted, members of this grouping have been described based largely on their ecological and morphological diversity, this variability is not consistently reflected by phylogenetic and phylogeographic evidence (Sanz 2018; Whiteley et al. 2019; Segherloo et al. 2021).

Despite a relatively recent diversification history spanning the period 0.5-2.5 Mya, brown trouts exhibit marked ecological and phenotypic variability throughout their large native range, which extends eastward from Europe and Northwest Africa to Russia and the Aral Sea basin. They occupy a wide range of habitats, from mountain streams and larger rivers to lakes and estuaries. Individual subpopulations can exhibit sedentary, anadromous or potamodromous life history strategies. Some freshwater systems are inhabited by multiple sympatric forms which differ in traits associated with foraging and reproductive ecology, and are sometimes referred to as "morphs", "ecomorphs" or "ecotypes" (Klemetsen et al. 2003; Kottelat & Freyhof 2007; Ferguson et al. 2019; Segherloo et al. 2021).

Some authorities have viewed this combination of factors to be representative of high species diversity and recognised around 50 nominal taxa, a number of which have been described this century (Kottelat & Freyhof 2007; Snoj et al. 2011; Sanz 2018). Alternatively, their systematics have been viewed from a phylogenetic and phylogeographic perspective based largely on mitochondrial DNA (mtDNA) analyses, with all subpopulations treated as a single polymorphic taxon customarily referred to as the “Brown Trout (Salmo trutta) complex” (Sanz 2018; Whiteley et al. 2019; Segherloo et al. 2021).

The latter approach led to brown trout diversity being defined by ten mtDNA lineages or sublineages corresponding to extensive catchments (the Danube, Atlantic, Mediterranean and Adriatic basins), specific geographic areas (the Balkan Peninsula and North Africa), individual watersheds (the Dades, Duero and Tigris rivers) and a distinctive phenotype (Marble Trout). Subsequent studies revealed that the distribution of some of these mtDNA lineages extends beyond their defined boundaries, e.g., the Adriatic lineage occurs from the Iberian Peninsula to the Republic of Türkiye, and the Marble Trout lineage is present in areas where no marbled phenotype exists, such as Corsica, central Italy, Albania and Greece (Bernatchez et al. 1992; Apostolidis et al. 1997; Bernatchez 2001; Suárez et al. 2001; Cortey & García-Marín 2004; Sušnik et al. 2005, 2007; Splendiani et al. 2006; Martínez et al. 2007; Snoj et al. 2009, 2011; Tougard et al. 2018; Schöffmann et al. 2022).

However, several studies have revealed the presence of mosaic distributions of mtDNA haplogroups among wild brown trout populations, plus mitochondrial-nuclear phylogenetic discordance in reconstructions made with both mitochondrial and nuclear trees (Snoj et al. 2009; Pustovhr et al. 2014; Leucadey et al. 2018; Splendiani et al. 2020). This suggests the presence of incomplete lineage sorting or asymmetric introgressive hybridization, which are common phenomena in rapidly diverging lineages and indicate that mtDNA genealogies might be generally unsuitable for defining phylogenetic relationships between brown trout taxa (Pustovhr et al. 2011, 2014). In the case of brown trouts, naturally intricate patterns of diversification and secondary contact shaped by repeated glaciations during the Pleistocene have been additionally complicated by widespread anthropogenic translocation and introgressive hybridisation since the Middle Ages (Largiadèr & Scholl 1996; Sanz et al. 2006; Lerceteau-Köhle et al. 2013). The combined use of multiple nuclear (nDNA, e.g., microsatellites, nuclear genes) and mitochondrial markers has already provided better insight into this complex scenario, resulting in progress towards a deeper understanding of evolutionary relationships at particular geographic scales or among subsets of putative taxa (Snoj et al. 2002, 2010, 2011; Sušnik et al. 2006, 2007; Berrebi et al. 2013, 2019; Gratton et al. 2014; Marić et al. 2017).

An integrative taxonomic approach combining morphological and ecological data with next generation sequencing of nDNA to identify genomic clusters may represent the most promising option for resolving brown trout systematics (Guinand et al. 2021; Segherloo et al. 2021). However, no comprehensive morphological or nDNA analyses have yet been completed, and it is plausible that the elaborate genetic and phenotypic diversity demonstrated by these fishes may never be adequately captured by a single accepted taxonomic system (Whiteley et al. 2019).

Pending a definitive outcome to the above, the Red List broadly follows the nomenclature provided by Fricke et al. (2024).

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

This species' population trend is uncertain, but there is no evidence of decline at a rate approaching the minimum threshold for Vulnerable under Criterion A (≥ 30% over 15 years = three generations). It does not approach the range thresholds for Vulnerable under Criterion B (extent of occurrence (EOO) < 20,000 km² or D2, and Criterion B2 is precluded by its uncertain area of occupancy (AOO). The population size exceeds 10,000 mature individuals, and thus does not approach the thresholds for Criteria C or D. There exists no quantitative analysis which would permit application of Criterion E.

Therefore, the Rhône Trout does not currently meet the thresholds for any Red List criteria, and it is assessed as Least Concern both globally and for the EU 27 member states.

This species is endemic to the Rhône River system in France and Switzerland, within which it is absent from the Lake Geneva (fr. lac Léman) basin. Molecular analyses have demonstrated that it is not present in small rivers east of the Rhône.

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

It is understood to have suffered a significant population size reduction during the 20^th century (see 'Threats'), but abundance may have increased at some locations since the 2000s due to conservation measures (see 'Conservation').

Genetic admixture with non-native Brown Trout lineages has occurred throughout most of its range over the past two centuries. A number of analyses have shown that the extent of introgression varies depending on location, ranging from relatively minor to total collapse of the native gene pool. This pattern could be the result of partial reproductive isolation, local habitat characteristics, and/or site-scale differences in the relative sizes of introduced and native stocks. The precise extent of these putative reproductive barriers and the traits that confer them have not yet been identified.

In terms of its native genetic structure, this species is included in the Mediterranean mitochondrial lineage within the Brown Trout (Salmo trutta) complex (see 'Taxonomic Notes'). Individuals inhabiting the upper Durance River in the lower Rhône catchment are composed of haplotypes belonging to the Adriatic Brown Trout lineage, and are thus more closely-related to subpopulations inhabiting the adjacent Po River system than to those elsewhere in the Rhône watershed.

This species inhabits a range of fluvial habitats, but is most commonly associated with relatively lotic middle-to-lower reaches of submontane river and stream channels. Non-hybrid individuals are today often restricted to tributary confluence zones, with hybrids dominating the intermediate stretches and non-native individuals inhabiting headwaters. Like other fluvial members of the Brown Trout complex, it demonstrates a preference for cool, well-oxygenated, low-nutrient environments with seasonal fluctuations in discharge. Substrata in such habitats tend to comprise a mixture of exposed bedrock, boulders, rocks, cobbles and gravel, with refuges in the form of overhanging riparian vegetation, undercut banks and woody structures such as branches, roots or fallen trees.

This species is a visual predator which feeds opportunistically on benthic and drifting invertebrates, e.g., Ephemeroptera, Diptera, Plecoptera, Trichoptera, while larger individuals also consume amphibian larvae and smaller fishes.

Adult individuals mature at age 4+, and the annual reproductive period comprises a spell of two to three weeks in late December. This species is iteroparous and potamodromous, and nuptial individuals display fidelity to specific upstream spawning sites comprising well-washed gravel beds in shallow, fast-flowing reaches. After arriving at these sites, individual females create shallow depressions (redds) in the substrate, into which the gametes are deposited. The presence of unclogged, well-oxygenated interstitial spaces within each redd is considered to be crucial for successful incubation and early development.

This species is primarily threatened by introgressive hybridisation with non-native Brown Trout (Salmo trutta), which has been introduced throughout its range for the development of recreational fisheries. The frequency of these activities increased dramatically with the development of aquaculture techniques during the late 19^th century, leading to tens of millions of alevins being stocked per year. The non-native individuals produced in hatcheries today are of mixed origin, but are typically derived from the Atlantic Brown Trout lineage (see 'Taxonomic Notes').

The non-native Rainbow Trout (Oncorhynchus mykiss) continues to be stocked in some parts of the Rhône system, and may constitute a threat through resource competition, predation on early life stages or introduction of pathogens.

The  Rhône Trout's decline has also been driven by river regulation and other forms of habitat degradation, which have resulted in widespread loss of the heterogeneous, interconnected fluvial habitats required to complete its life cycle. In particular, the construction of dams, weirs and other barriers has altered natural flow and sedimentation regimes, blocked access to spawning sites, fragmented subpopulations, and generally reduced the extent of suitable habitat for all life stages. The quality of habitat has been further diminished by bank stabilisation, channelisation and other efforts to enhance flood protection or exploit water for human development. Furthermore, the increase in habitat homogeneity associated with these modifications is understood to reduce reproductive isolation between native and introduced trouts.

Hydroelectric dams have created regular fluctuations in discharge and water temperature (hydropeaking and thermopeaking) which cause dewatering of spawning sites, the loss of stable nursery habitat for juveniles, and downstream displacement, while unstable flow and temperature regimes may also increase hybridisation rates. The combined effect of hydropeaking, dam flushing operations, changes in land use, and the removal of riparian vegetation has also increased accumulation of fine sediments at spawning sites, thus impairing the hatching and survival rates of eggs and larvae.

The industrial extraction of riverine gravel and other sediments for urban development is likely to have further reduced the extent and quality of available spawning sites.

This species is also understood to be threatened by diffuse and point source agricultural, domestic and industrial pollution, which has resulted in eutrophication or discharge of toxic substances at some locations.

Rising water temperatures due to climate change represent a plausible threat, since they may interfere with food availability, lifespan, and the timing of reproductive processes, with the latter potentially leading to greater overlap with non-native Brown Trout.

This species is a key component of recreational fisheries throughout its range, where fly-fishing for both native and non-native trouts is a multi-million Euro industry.

This species was assessed as Endangered for the 2022 Swiss National Red List of Freshwater Fishes and Cyclostomes.

It is present within the boundaries of numerous protected areas, some of which are included in the European Union's Natura 2000 network.

In France, stocking with non-native trout has been progressively abandoned since the 1990s in order to preserve and restore native subpopulations. Moreover, a series of positive conservation outcomes have been achieved through a collaborative research initiative between scientists and fisheries managers in the Haute-Savoie Department, which resulted in a number of different conservation management strategies being trialled and/or successfully implemented at various sites in the Rhône River catchment. These methods include the establishment of genetic refuges which are no longer stocked with non-native trout, translocation of genetically-pure individuals from downstream to upstream reaches, and stocking with alevins reared from gametes of native genetic provenance.

This species' conservation has been further aided by a commitment to thorough genetic screening of wild trout subpopulations and hatchery broodstocks throughout France, with the results made available via an online database which includes a detailed map of sampled locations displaying the genetic structure of resident subpopulations. This project has been backed by a series of high profile stakeholders including the French Ministry of Ecological Transition and National Centre for Scientific Research, and is used to establish best practices, guide management priorities and ensure the genetic integrity of stocked alevins.

At some locations, this species may have benefitted from benefitted from actions to improve the ecological status of rivers within the framework of the European Water Framework Directive 2000/60/EC. It might also have been favoured by extensive management efforts undertaken for the Rhône Streber (Zingel asper) since the 1990s, which have included the restoration of gravel beds and improvement of connectivity through barrier removal or the installation of fishways in some parts of the Rhône watershed.

Daily bag limits and minimum catch sizes are established for recreational fisheries, and there is an annual closed season extending from October 1 to the end of February. Some river stretches are strict no-kill fisheries.

Recent research based on the Rhône Trout has highlighted the potential for management efforts that specifically target environments favouring native intraspecific diversity through eco-evolutionary processes such as postzygotic selection.

In addition, it has been widely recommended that the conservation management of European trouts must be considered independent of their systematic classification, due to a lack of consensus regarding their taxonomy plus the existence of notable microgeographic genetic and phenotypic diversity (see 'Taxonomic Notes'). Each subpopulation should therefore be assessed individually, taking into account its evolutionary and genetic significance coupled with the ongoing population trend and threats, to result in a priority ranking permitting the effective allocation of conservation resources through the development of site-specific, catchment-scale management plans. Sympatric morphological forms should also be managed separately, depending on their respective habitat preferences, diets and life histories. The abundance trends of many subpopulations remain unknown, and their individual assessments should ideally form the basis of future research efforts in order to ensure appropriate prioritisation. In practice, such efforts will be most efficiently coordinated at local, national or regional scales.