Genus of fishes
Thymallus, commonly known as graylings, is a genus of freshwater ray-finned fish and the only genus within the subfamily Thymallinae of the family Salmonidae. Although all "Thymallus" species can be generically called graylings, without specific qualification the term "grayling" typically refers to the type species "Thymallus thymallus", the European grayling.
Name.
The name of the genus "Thymallus" first given to grayling ("T. thymallus") described in the 1758 edition of "Systema Naturae" by Swedish zoologist Carl Linnaeus originates from the 
faint smell of the herb thyme, which emanates from the flesh. "Thymallus" derives from the Greek θύμαλλος, "thyme smell".
Species.
According to FishBase, 14 species are placed in this genus. However, views differ on their taxonomic rank.
Modern reviews and the "Catalog of Fishes" also list additional species including "[[Thymallus nikolskyi]" Kaschenko, 1899, "[[Thymallus baicalolenensis]]" Matveyev et al., 2005 and "[[Thymallus ligericus]]" Persat et al, 2019. An old controversy exists over the status of Baikal black vs white graylings, "T. baicalensis" and "T. brevipinnis". Modern research supports the view that they are not separate taxa, but alternative ecological forms of "T. baicalensis".
Distribution.
The fishes of this genus are native to the northern parts of the [[Palearctic realm|Palearctic]] and [[Nearctic realm]]s, ranging from the [[United Kingdom]] and northern [[Europe]] across [[Eurasia]] to [[Siberia]], as well as northern [[North America]]. "T. thymallus", the grayling, is widespread in Europe, and "T. arcticus," the Arctic grayling, is widespread throughout Eurasia east of the [[Ural Mountains]] and in the Nearctic. The other species have more localized ranges in northern Asia.
Appearance.
"Thymallus" species are distinguished from other members of the [[salmonidae|salmonid family]] by their larger scales, their small mouths with [[teeth]] on the [[maxilla]]ry bone, and most striking of all, their showy, sail-like [[dorsal fin]]s. This fin is longer in males and highly colourful, with spots of red, orange, purple or green. The body is also colourful; the dorsal surface is a dark purplish to bluish black or gray, grading to dark blue or silver gray on the flanks and gray or white on the belly. The body is further decorated with a smattering of small dark spots; these are much more numerous in juveniles.
[[File:Grayling caught in the Colville River. North Slope, Alaska.jpg|thumb|260 px|alt=Arctic Grayling|Four [[Arctic grayling]] ("T. arcticus") from the [[Colville River (Alaska)|Colville River]] of Alaska]]
The longest of the graylings is the Arctic grayling, "T. arcticus", at a maximum length of and a maximum weight of . "T. thymallus," while somewhat shorter - - may weigh significantly more, . The fishes of this genus may live for 18 years or more.
Ecology and reproduction.
These fishes require cool, well-oxygenated water, preferably with a swift current; they are found in large, sandy- or gravel-bottomed rivers and lakes, but "T. thymallus" may occasionally be found in [[brackish]] conditions. Generally [[omnivorous]], they feed primarily on [[crustaceans]], [[insects]], and [[zooplankton]].
The grayling species, typically for [[Salmonidae|salmonids]], spawn in rivers and do not guard their brood, although they do conceal their eggs in silt. The spawning behavior of the Arctic grayling may be typical for the genus "Thymallus".
As they are highly sensitive to changes in water quality, "Thymallus" fishes may be considered [[indicator species]]; "T. arcticus" has largely disappeared from the [[Great Lakes Basin]].
Human use.
[[Image:Harjus.JPG|thumb|260px|Catch of [[Thymallus thymallus|grayling]] ("Thymallus thymallus"), [[Sápmi|Lapland]]]]
Due to their agreeable taste and attractive form, the grayling species are valued as food and game fishes, and they are occasionally seen in [[public aquaria]]. The most economically important of these fishes, for which [[fishery|fisheries]] and [[aquaculture]] operations exist, are the grayling ("T. thymallus") and the Arctic grayling ("T. arcticus").
References.
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[[Category:Thymallus| ]]
[[Category:Extant Pleistocene first appearances]]
[[Category:Ray-finned fish genera]]
[[Category:Fauna of the Holarctic realm]]