The ciscoes (or ciscos) are salmonid fish of the genus Coregonus that differ from other members of the genus in having upper and lower jaws of approximately equal length and high gill raker counts. These species have been the focus of much study recently, as researchers have sought to determine the relationships among species that appear to have evolved very recently. The term cisco is also specifically used of the North American species Coregonus artedi, also known as lake herring.

Fluorescence in situ hybridization (FISH) is a laboratory technique for detecting and locating a specific DNA sequence on a chromosome. The technique relies on exposing chromosomes to a small DNA sequence called a probe that has a fluorescent molecule attached to it. All fish share two traits: they live in water and they have a backbone—they are vertebrates. Apart from these similarities, however, many of the species in this group differ markedly from one.

In previous taxonomic classifications, the ciscoes have been identified as a subgenus Leucichthys of the genus Coregonus. Based on molecular data this is not a natural classification however, as the ciscoes are polyphyletic, comprising two different lineages within the freshwater whitefishes.^[1]

Continental North American ciscoes: Coregonus artedi sensu lato[edit]

Eight taxa of cisco have been recognized in the LaurentianGreat Lakes and other interior lakes of the once-glaciated North America.^[2]

• †Longjaw cisco – Coregonus alpenae
• Cisco (lake cisco, northern cisco, or lake herring) – Coregonus artedi
• †Deepwater cisco – Coregonus johannae
• Bloater – Coregonus hoyi
• Kiyi – Coregonus kiyi
• †Blackfin cisco – Coregonus nigripinnis
• Shortnose cisco – Coregonus reighardi (possibly extinct)
• Shortjaw cisco – Coregonus zenithicus

Usually, several taxa of ciscoes are found in a single lake. They exhibit different habitat distributions, feeding and breeding habits and morphological adaptations e.g. in their gill raker numbers. In the Great Lakes, at least five ciscoes coexist.^[3]

According to genetic analyses, these cisco types do not represent unique, separate evolutionary lineages, but similar cisco morphs have evolved and attained their specific characteristics largely independently in each lake. Therefore, it has been suggested that they should not be recognized formally as distinct taxa, but all considered members of a single species, Coregonus artedi (sensu lato).^[3] or Coregonus artedi complex. Nevertheless, for conservation and management purposes the sympatric morphs in each lake should be considered ESUs, evolutionarily significant units.^[3] This taxonomic view is not widely accepted however, which has complicated discussions of the conservation status of some species.^[4]

Ciscoes have been exploited in commercial fisheries, particularly in the Laurentian Great Lakes where the deepwater forms were the basis of the so-called chub fishery. The chub fishery had nothing to do with the various cyprinid fish species known as chubs but was exclusively based on the various species of ciscoes. The fishery continued as cisco stocks fell and non-native species such as sea lamprey, rainbow smelt and alewife spread through the system and increased in abundance. Alewife, in particular, have been implicated as a predator of cisco eggs and larvae, and as a competitor with ciscoes. The fishery shifted focus from species to species as cisco numbers declined and has been largely defunct for some years.

Ciscoes of northwestern North America[edit]

Three species of cisco inhabit waters of the northwestern North America. These have been found to represent distinct evolutionary lineages, by genetic data.^[3]

• Arctic cisco – Coregonus autumnalis
• Bering cisco – Coregonus laurettae
• Least cisco – Coregonus sardinella

Eurasian ciscoes[edit]

The ranges of the three cisco species above extend across Beringia to the Asian coasts. Of those the Arctic cisco and least cisco (=sardine cisco) are widespread through northern Siberia. In the inland waters of northern Europe, the European cisco or vendace (Coregonus albula) replaces the Siberian sardine cisco. Some of the cisco lineages are genetically very close, such as the European and sardine ciscoes. Within some species, geographically separated populations have been treated as distinct taxa, despite close genetic relationships, such as the vendace and the pollan (Arctic cisco) on the British Isles. The European cisco has also evolved into ecologically distinct sympatric populations or ecomorphs independently within several lakes (e.g. autumn and spring spawning populations, normal and dwarf morphs), which have been designated as distinct taxa, making the systematics complicated as with the North American Coregonus artedi complex.

• Bering cisco – Coregonus laurettae
• Arctic cisco – Coregonus autumnalis
  • Irish pollan - 'Coregonus pollan': an Irish subspecies or group of populations
• Sardine cisco (= least cisco) – Coregonus sardinella
• Peled – Coregonus peled: part of the C. sardinella complex^[5]
• European cisco (=vendace) – Coregonus albula
  • 'Coregonus vandesius': group of British populations
  • Stechlin cisco – Coregonus fontanae: local sympatric spring spawning dwarfed sister species
  • Coregonus trybomi: local sympatric spring-spawning sister species
  • Coregonus lucinensis: local sympatric dwarfed sister species

Phylogeny[edit]

Based on molecular data from mitochondrial DNA, the ciscoes comprise two distinct, unrelated groups:^[1]

• The Coregonus artedi complex along with C. laurettae and C. autumnalis lineages
• The Coregonus sardinella complex, including C. peled and C. albula. This group is more closely related to the 'true whitefishes' (e.g. the common whitefishC. lavaretus, lake whitefishC. clupeaformis) than to the C. artedi complex ciscoes.

References[edit]

• Froese, Rainer and Pauly, Daniel, eds. (2004). Species of Coregonus in FishBase. October 2004 version.

1. ^ ^abBernatchez L, Colombani F, Dodson JJ (1991) Phylogenetic relationships among the subfamily Coregoninae as revealed by mitochondrial DNA restriction analysisJournal of Fish Biology 39 (Suppl A):283-290.
2. ^Scott, W.B., Crossman, E.J. (1973) Freshwater Fishes of Canada. Bull. Fish. Res. B. Canada 184, 1–1092
3. ^ ^abcdTurgeon, J. & Bernatchez, L. (2003) Reticulate evolution and phenotypic diversity in North American ciscoes, Coregonus ssp. (Teleostei: Salmonidae): implications for the conservation of an evolutionary legacyArchived 2015-01-22 at the Wayback MachineConservation Genetics 4: 67–81
4. ^COSEWIC (2007). COSEWIC assessment and update status report of the blackfin cisco Coregonus nigripinnis in Canada Committee on the Status of Endangered Wildlife in Canada. vi + 23 pp
5. ^Politov DV, Bickham JW, Patton JC (2004) Molecular phylogeography of Palearctic and Nearctic ciscoes. Ann. Zool. Fennici 41:13-23.

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