Fish That Scientists Thought Was Extinct Is Actually Abundant, Study Finds

A species of fish thought to have gone extinct 15 years ago has surprised scientists after being found living happily in the wild.

The houting, a whitefish species found throughout estuaries in the North Sea, was declared officially extinct in 2008.

Now, researchers have used DNA taken from specimens of houting in the Natural History Museum in London and compared it to a species living in the wild—the European whitefish. They found that they were genetically so similar that they could be considered to be part of the same species.

So, the houting is not extinct after all, and is in fact abundant, a new paper published in the journal BMC Ecology and Evolution reveals.

"Linnaeus [Carl Linnaeus, one of the founders of modern taxonomy] already made a species distinction between houting from the North Sea that migrate between sea and rivers (C. oxyrinchus) and whitefish that only live in freshwater (C. lavaretus)," first author of the paper and Ph.D. researcher in biodiversity and ecosystem dynamics at the University of Amsterdam, Rob Kroes, told Newsweek.

"The migratory houting disappeared in the 1940s from almost every river system, mainly because of habitat change and fisheries, and was therefore considered extinct by many. In 2005, [other researchers] did a morphological study on the migratory houting that were stored in the NHM [Natural History Museum in London] and claimed that they were indeed a separate species from specimens that are found to date. The IUCN [International Union for Conservation of Nature] accepted this claim."

As a result, the houting was officially classed as extinct.

However, many scientists questioned the claim since small populations of migratory houting were still present in the North Sea basin.

"Also, the morphological traits from the [other] study are quite unsuitable for species distinction since they can vary highly within species," Kroes said. "However, nobody really knew if both recent freshwater and migratory houting or whitefish differed from the 'extinct' houting that are stored in the NHM since nobody compared the DNA of all these fish. We are the first to do so. Our conclusion: they are all the same species, differences in traits and migratory behaviour are just within-species variation. So both the extinct claim and the species distinction are incorrect."

Occasionally a species that is not extinct is declared to be extinct, often because it is unclear if different specimens are the same species or different species, the authors explain in the BMC Ecology and Evolution paper.

"Coregonids that are found in and around the North Sea and Baltic Sea are named whitefish, common whitefish, European whitefish, houting or North Sea houting, depending on the geographical location where the fish is found, for example," Kroes said. "This also applies to the scientific name that are addressed to these fish: C. oxyrinchus and C. lavaretus and sometimes C. marenae. However, if you compare all these fish by their morphological traits or DNA they don't differ that much."

"Several studies therefore already questioned the extinct status of C. oxyrinchus," he said. "But until now, nobody compared the DNA of recently observed houting and houting from the NHM that were used by taxonomists for the species description and distinction between C. oxyrinchus and C. lavaretus. This triggered us to perform the DNA analysis on both recent and ancient specimens."

The researchers made their discovery by comparing mitochondrial DNA—also known as mtDNA—of houting specimens in museums with current European whitefish. mtDNA is DNA inside the mitochondria in our cells, which are only passed down the female line. The researchers even managed to extract mtDNA from dried North Sea houting dating back to 1754. They then created a phylogenetic tree using the DNA, finding that the houting (Coregonus oxyrinchus) ended up in the same species grouping as European whitefish (Coregonus lavaretus).

"Our mtDNA sequence analysis shows that all older and recent Coregonus spp., formerly classified as C. oxyrinchus and C. lavaretus respectively, clustered together and did not form separate clades or lineages in the phylogenetic tree. This conclusion is supported by the low bootstrap values on branches," the authors wrote in their paper.

"Also, the older C. oxyrinchus show no monophyletic geographic distribution in comparison to the recent obtained C. lavaretus. Statistical analysis on the CytB and ND3 haplotype network further supports our conclusion," they wrote.

This means that the houting is definitively no longer extinct, and that the Latin name of the species may need to be changed. This will require additional research using the DNA of the 1754 specimen, however, as this was used by Linnaeus for the official species description.

"The DNA is old and damaged, but I think we should try. At the moment, the protected status of various coregonids is a mess," Kroes said in a statement. "According to the IUCN, North Sea houting is extinct; at the same time, there are various European nature laws that state that both houting and European whitefish must be protected. So we are actually protecting an extinct species that is just swimming around at the moment."

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