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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. 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.〔Bernatchez L, Colombani F, Dodson JJ (1991) (Phylogenetic relationships among the subfamily Coregoninae as revealed by mitochondrial DNA restriction analysis ) ''Journal of Fish Biology 39 (Suppl A):283-290.〕 ==Continental North American ciscoes: ''Coregonus artedi'' sensu lato== Eight taxa of cisco have been recognized in the Laurentian Great Lakes and other interior lakes of the once-glaciated North America.〔Scott, W.B., Crossman, E.J. (1973) Freshwater Fishes of Canada. ''Bull. Fish. Res. B. Canada'' 184, 1–1092〕 * 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'' * 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.〔 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).〔 or ''Coregonus artedi'' complex. Nevertheless for conservation and management purposes the sympatric morphs in each lake should be considered ESUs, evolutionarily significant units.〔 This taxonomic view is not widely accepted however, which has complicated discussions of the conservation status of some species.〔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〕 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cisco (fish)」の詳細全文を読む スポンサード リンク
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