This species has been referred to as Coregonus sp. "Albock", C. sp. "Bodenalbock", C. sp. "Schwebalbock", C. sp., "Tiefenalbock", C. sp. "Wanderalbock", C. sp. "Felchen" and C. sp. "Large type" in some published literature.

It has also been treated as a subpopulation of the Bourget Whitefish (Coregonus lavaretus) or a member of the "Coregonus lavaretus species complex", and referred to by the English vernacular names "Common Whitefish" or "European Whitefish" (see below).

At the regional scale, the systematics of European ciscoes and whitefishes (Coregonus spp.) has been the subject of considerable debate since the turn of the 21^st century, with little indication of a definitive outcome.

It is widely accepted that non-anadromous members of this group have repeatedly undergone adaptive radiations in boreal, subarctic and perialpine lakes (Douglas et al. 1999, Østbye et al. 2005, Kahilainen and Østbye 2006, Harrod et al. 2010, Hudson et al. 2011).

Subpopulations inhabiting these systems largely diversified in the wake of the most recent glacial period 10,000-15,000 years ago. They are typified by parallel patterns of divergence in traits associated with foraging (i.e., gill raker counts, benthic vs. pelagic feeding ecology), physiology (i.e., growth rate, habitat depth partitioning) and reproductive ecology (i.e., reproductive timing and spawning habitat).

Up to six different sympatric forms sometimes referred to as “morphs”, "ecomorphs" or "ecotypes" have been recorded in perialpine lakes, and these radiations might be even more diverse in some large systems of northeastern Europe (Præbel et al. 2013, Doenz et al. 2018, Bitz‐Thorsen et al. 2020, Öhlund et al. 2020).

However, there exist significant differences in opinion regarding the taxonomic status of these forms.

In Northern Europe, including the United Kingdom, all except a handful of Irish subpopulations are usually regarded as belonging to two widely-distributed species; Coregonus albula (ciscoes) and C. lavaretus (whitefishes), with the latter also frequently referred to as the "Coregonus lavaretus species complex” (Etheridge et al. 2012, Wanke et al. 2017, Häkli et al. 2018, Crotti et al. 2020). Within this comparatively uniform taxonomic concept, the catch-all English vernacular name “Vendace” is typically used for C. albula while "Common Whitefish" or "European Whitefish" are applied to C. lavaretus.

Conversely, researchers and fisheries authorities based in Central Europe have tended to treat the different forms as distinct taxa, leading to the recognition of more than 60 species across the European region (Kottelat and Freyhof 2007, Selz et al. 2020, De-Kayne et al. 2022, Selz and Seehausen 2023). Under this diverse taxonomic concept, the name “Vendace” is restricted to its original usage for the United Kingdom endemic Coregonus vandesius and the native range of C. lavaretus is limited to its type locality of Lake Bourget in France.

In the absence of a region-wide consensus, the Red List continues to follow the taxonomy provided by Fricke et al. (2024).

Global and European regional assessment: Vulnerable (VU)
EU 27 regional assessment: Not Recorded

Fatio's Whitefish is endemic to lakes Brienz and Thun, Switzerland. The species has a restricted range (extent of occurrence (EOO) c. 230 km², area of occupancy (AOO) c. 78 km²), which meets the thresholds for the Endangered category under Criterion B1 (EOO < 5,000 km²) and Criterion B2 (AOO < 500 km²). It is restricted to two locations, but there is no indication of continuing decline or extreme fluctuations, hence it does not qualify for a threatened category under Criterion B.

There is no evidence of any population size reduction that would approach the threshold for Vulnerable under Criterion A (≥ 30% over the past ten years or three generations). The population size does not approach the thresholds for Vulnerable under Criterion C (< 10,000 mature individuals) or D1, and there exists no quantitative analysis of extinction probability which would permit application of Criterion E.

Therefore, this species is assessed as Vulnerable under Criterion D2, based on its presence at two locations, threatened by the introduction of non-native species that could drive it to Critically Endangered or Extinct in a very short time period.

This species is endemic to lakes Brienz (de. Brienzersee) and Thun (de. Thunersee) in the upper Rhine River system, Switzerland.

This species' population size is unknown, but it is understood to exceed the minimum threshold for Red List criteria (< 10,000 mature individuals). The current population trend has not been quantified, but there is no indication of continuing decline.

Lakes Brienz and Thun are perialpine, oligotrophic lakes formed after the last glacial period. Lake Brienz has a maximum depth of 260 metres and is connected to Lake Thun, which has a maximum depth of 217 metres, via the Bödeli Aare River.

Seven whitefish species which differ in traits related to feeding and reproductive ecology along depth gradients are native to these lakes. Three are endemic to Lake Thun, one is endemic to Lake Brienz, and three are present in both lakes.

Current knowledge suggests that Fatio's Whitefish occupies both the benthic and pelagic zones, and can occur from a few metres depth to the deepest parts of both lakes.

This species feeds predominantly on zooplankton alongside some benthic prey and has a moderately fast growth rate.

The annual reproductive period is lengthy, with two peaks extending from August to October and December to March, respectively.

Spawning occasionally takes place in shallow water of up to 10 metres depth, but most commonly occurs at depths of c. 40-261 metres in Lake Brienz and c. 40-217 metres in Lake Thun, depending on the season.

This species is targeted by the commercial fishery operating in Lake Thun, therefore overexploitation is considered to represent a plausible threat.

Several native whitefish species are reared artificially for supplemental stocking in Lake Thun, and there is evidence to suggest that hybridisation is occurring in hatchery facilities (see 'Use and Trade'). The impact of hybrid individuals being released into the lake has not been studied in depth, but could plausibly be driving a loss of inter- and intraspecific genetic diversity through introgression with wild stocks.

Whitefishes from Lake Thun have been reported to exhibit malformations in gonad morphology, which research suggests is related to feeding on native zooplankton. It remains unclear if internal or external components of the zooplankton are responsible for these changes. The prevalence of these deformities appears to have receded in recent years, and there is no evidence of a negative effect on reproduction.

During the 20^th century, lakes Brienz and Thun both became enriched with nutrients due to discharge of domestic sewage. This process is likely to have exerted a profound effect on whitefish population structure and selection, but is not currently considered to represent a threat (see 'Conservation').

Plausible future threats include warming of the lakes due to climate change, and introduction of non-native aquatic species such as the Quagga Mussel (Dreissena bugensis), which is currently expanding in Switzerland and may colonise whitefish foraging and spawning sites.

Whitefishes are harvested commercially in both lakes, but in Lake Brienz fishing pressure is low since only a single part-time fisher is currently active.

Recreational angling is also permitted, with daily bag and minimum size limits for whitefishes in place, plus an annual closed season which extends from October 1 to December 31.

Lake Thun is stocked with large numbers of juvenile whitefishes on an annual basis. To facilitate this activity, gametes are stripped from wild adults during the winter spawning period and transported to hatchery facilities for artificial fertilisation and rearing. Among the native whitefish species, the Point-Snouted Whitefish (Coregonus acrinasus), Alpine Whitefish (C. alpinus) and Steinmann's Whitefish (C. steinmanni) are often caught together at this time due to their similar reproductive ecology. Fisheries managers do not make a distinction between them, so it is likely that a significant proportion of hatchery-reared individuals comprise hybrids (see 'Threats').

Fatio's Whitefish is not intentionally utilised for stocking purposes, but a few individuals are probably stripped each year because its spawning sites partially overlap with those of the Point-Snouted Whitefish.

This species is included (as Coregonus spp.) in Appendix III of the Bern Convention.

Investment in wastewater treatment facilities since the 1990s has driven an improvement in the water quality of lake Brienz and Thun, which have returned to their former oligotrophic states.

Recreational angling is permitted in both lakes, with daily bag and minimum size limits for whitefishes in place. There are annual closed seasons running from November 1 to December 31 in Lake Brienz, and from October 1 to December 31 in Lake Thun.

The stocking of non-native whitefishes has been prohibited in Lake Thun since 1946, and in Lake Brienz since 1991.

A deeper understanding of this species' population trend and life history, plus the impacts of harvesting and stocking in Lake Thun may be of use for future management planning.