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The mystery of whitefish diversity: Why do scientists argue over the species classification of Coregonus?
In aquatic ecosystems, fish of the genus Coregonus, commonly known as whitefish, are undoubtedly the focus of countless discussions and controversies among scientists. These fish belong to the salmon family, which includes at least 68 described living species. Despite this, the true number of these species remains controversial.
The diversity of the genus Coregonus not only reflects the challenges of taxonomy, but also reveals the complexity of my country's aquatic ecology.
The typical species of Coregonus is the common whitefish (Coregonus lavaretus). Most of these fish live in lakes and rivers, and some species, such as the Arctic herring (C. autumnalis), Bering herring (C. laurettae) and least herring (C. sardinella), are migratory fish that can move freely between salt and fresh water. But over the past century, several whitefish species, especially from the Great Lakes and European Alpine lakes, have become extinct or endangered.
Coregonus is one of six of the 12 freshwater fish species listed as extinct, according to European reports. This has raised attention to the importance and urgency of their conservation. All Coregonus species are protected in Appendix III of the Berne Convention and in Appendix IV of the EU Habitats Directive (92/43/EEC).
The Challenge of TaxonomyBased on phylogenetic evidence, the most basal member of the genus Coregonus is the highly endangered C. huntsmani, a species restricted to a single river basin in Nova Scotia, Canada. Remarkably, the appearance of this fish dates back to the Middle Miocene, about 15 million years ago.
Traditionally, Coregonus is subdivided into two subgenera: Coregonus ("true whitefish") and Leucichthys ("bluefish"). This classification is not perfect, and evidence from molecular data shows that black carp actually consists of two different phylogenetic branches within the genus. Furthermore, the genus name Stenodus is not phylogenetically distinct from Coregonus. The latest research indicates that C. huntsmani is even more ancient than Stenodus.
Such taxonomic puzzles not only demonstrate the complexity of phylogeny, but also trigger fundamental thinking about the definition of species.
The perspective of species diversity
The taxonomy of the genus Coregonus is fraught with uncertainty, particularly in Europe and North America. Some scholars believe that there are only two main species in the genus: the common whitefish (C. lavaretus) and the small whitefish (C. albula), while others divide it into dozens of relatively narrowly distributed species. In 2007, a review report proposed that more than 50 local European populations should be considered separate species based on morphological differences. In fact, the genetic differences between these species are relatively limited and sometimes do not have monophylogenetic characteristics.
A survey of whitefish in the UK found that the identification keys provided in 2007 did not match the majority of individuals and further evidence was needed to support the presence of the species in the area. The presence of multiple forms of Coregonus in many European lakes, which differ ecologically and morphologically, particularly in the number of gill combs, and are to some extent partially reproductively isolated, has led to the suggestion of their recognition as hierarchical species.
The rapid integration of species is also one of the major challenges for biodiversity conservation under modern environmental changes.
Conservation Importance and Actions
As environmental changes accelerate, Coregonus' forms may disappear or merge into a single form in just 15 years, meaning the end of three generations of Coregonus evolution. A similar situation has been found in the Great Lakes of North America, where the Coregonus artedi complex has multiple morphologically distinct and often coexisting ecotypes, and their taxonomic status remains controversial.
The 2017 FishBase website lists 78 species of Coregonus, some of which are marked as extinct. Not only that, maintaining attention and protection for these species will also have a profound impact on the overall health of aquatic ecosystems.
To resolve the debate over the classification of Coregonus species, the scientific community needs to combine a biological perspective with environmental monitoring to understand the diversity of these fish and why they are needed for research. So, what kind of contribution can we make to the future of Coregonus?
