Coregonus lavaretus

 ( Lavaretus ) 

The Danish houting is genetically part of the widespread Coregonus lavaretus Species complex (including Coregonus maraena of the Baltic Sea basin; some prefer to include the Danish houting in this species), while its genetic relationship to the extinct population cannot be confirmed due to a lack of sufficient samples of the latter.Jacobsen M.W.; Hansen M.M.; Orlando L.; Bekkevold D.; Bernatchez L.; Willerslev E.; and Gilbert M.T. (2012). Mitogenome sequencing reveals shallow evolutionary histories and recent divergence time between morphologically and ecologically distinct European whitefish (Coregonus spp.). Mol Ecol. 21(11): 2727–2742. Nevertheless, there are some minor differences in the genetics of the Danish houting compared to other living members in the C. lavaretus complex, as well as the differences in morphology and ecology, making it an evolutionarily significant unit.Dierking, J.; L. Phelps; K. Præbel; G. Ramm; E. Prigge; J. Borcherding; M. Brunke; and C. Eizaguirre (2014). Anthropogenic hybridization between endangered migratory and commercially harvested stationary whitefish taxa (Coregonus spp.). Evol Appl. 7(9): 1068–1083. Hybridization and introgression between North Sea houting and its relatives is well-documented, and likely the result of translocations of Coregonus between different regions by humans. Some researchers argue that the morphological differences between different houting populations are not exceptional within the broader variation of the European whitefish, and probably no species-level extinction has taken place.Vinter, H.V. (2017). Taxonomische status van houting in Nederlandse wateren. Taxonomic. Wageningen University & Research Rapport C115/17. The primary reason for treating the Danish houting and the extinct houting as separate are differences in the number of gill rakers (on average, the Danish has fewer than the extinct), but this number can vary extensively in Coregonus, even within a single population and species,Christensen, G.H. (2010). Danmarks ferskvandsfisk Denmark's. pp. 47–48. and genetic studies of Coregonus have shown that gill rakers are of limited use in predicting relationship among populations.Østbye K.; Bernatchez L.; Naesje T.F.; Himberg K.J.; and Hindar K. (2005). Evolutionary history of the European whitefish Coregonus lavaretus (L.) species complex as inferred from mtDNA phylogeography and gill-raker numbers. Mol Ecol. 14(14):4371-4387. Ozerov, M.Y.; M. Himberg; T. Aykanat; D.S. Sendek; H. Hägerstrand; A. Verliin; T. Krause; J. Olsson; C.R. Primmer; and A. Vasemägi (2015). Generation of a neutral FST baseline for testing local adaptation on gill-raker number within and between European whitefish ecotypes in the Baltic Sea basin. Journal of Evolutionary Biology 28(5): 1170–1183. Some think that the morphological differences in number of gill rakers are sufficient for treating them as separate, and that the last true houting was caught in the lower Rhine in 1940. Studies in the early 2000s (decade) indicated that there was no overlap in the possible number of gill rakers of the two (28–35 in the Danish; 38–46 in the extinct), but later reviews have shown that there is an overlap (up to 41 has been found in the Elbe, a reintroduced population based on Danish houting).Ramm, G.; and J. Dierking (2014). - Gill raker morphometry - Gesine Ramm.pdf/ http://oceanrep.geomar.de/23735/1/Report - Gill raker morphometry - Gesine Ramm.pdf. Geomar, Helmholtz Centre for Ocean Research Kiel.

A €13 million restoration project of the Danish houting, partly funded by the European Union's LIFE programme and the Danish Natural Agency, was undertaken in 2005–2013, The houting project – The second largest nature restoration project in Denmark naturstyrelsen.dk (the Danish Nature Agency) Snæbelprojekt – Naturgenopretningsprojekt for en af EU's mest truede fiskearter naturstyrelsen.dk (the Danish Nature Agency) and there is ongoing monitoring of the species and regulation of the fish-eating great cormorant from important locations.Svendsen, J.C.; A.K.O. Alstrup; and L.F. Jensen (11 April 2018). Save a North Sea fish from becoming museum piece. Nature. Retrieved 12 April 2018. As of 2019, a total of more than €20 million has been used on its conservation, with almost two-thirds funded by Denmark and the remaining by the European Union.Mandrup, L., and N.M. Jørgensen (26 April 2019). Efter redningsaktioner for 150 mio. kr.: Danmarks mest sjældne fisk er i lille fremgang. After. DR News. Retrieved 26 April 2019. However, the only remaining fully natural and significant population of Danish houting is in the Vidå River, estimated in 2014 to consist of about 3,500 adults. Little is known about its exact spawning and juvenile requirements, and despite the earlier project it was still declining, leading to fears that it could become fully extinct unless more is done to preserve it. After years with a downward trend in its numbers, an increase to about 4,000 adult Danish houtings was registered in 2018–19, with most individuals in the Vidå and fewer in (both populations increasing).

Individuals from the Danish population have been used as a basis for re-establishing houting in the Eider, Elbe (both indisputably a natural part of the range) and Rhine (arguably non-native, if the extinct is recognized as a separate species).Borcherding, J.; M. Heynen; T. Jäger-Kleinicke; H. V. Winter; and R. Eckmann (2010). Re-establishment of the North Sea houting in the River Rhine. Fisheries Management and Ecology 17(3): 291–293. Borcherding, J.; A. W. Breukelaar; H. V. Winter; and U. König (2014). Spawning migration and larval drift of anadromous North Sea houting (Coregonus oxyrinchus) in the River IJssel, the Netherlands. Ecology of Freshwater Fish 23(2): 161–170. On the 24th of October 2023 researchers of the Research Institute for Nature and Forest in Belgium captured a live specimen in the Scheldt in Kruibeke, while the species was thought to be extinct in the country for over 100 years. Possibly the specimen migrated there from the Rhine population. In Annex II of the EC Habitats Directive (92/43/EEC), a species listed as Coregonus oxyrhynchus is protected for 'anadromous populations in certain sectors of the North Sea'

In 2023, DNA analysis found the houting to be genetically indistinguishable from Coregonus lavaretus, and therefore not extinct.