Amur Grayling

''Thymallus'' is a genus of freshwater fish in the salmon family Salmonidae; it is the only genus of subfamily Thymallinae. The type species is ''Thymallus thymallus,'' the grayling. The species in the genus are generically called graylings, but without qualification this also refers specifically to ''T. thymallus.''

Distribution

The fishes of this genus are native to the northern parts of the Palearctic and Nearctic realms, 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 salmon family by their larger scales, their small mouths with teeth on the maxillary bone, and most striking of all, their showy, sail-like dorsal fins. 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.

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 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

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 fisheries and aquaculture operations exist, are the grayling (''T. thymallus'') and the Arctic grayling (''T. arcticus'').

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.
* ''Thymallus arcticus'' (Pallas, 1776) - Arctic grayling
* '' Thymallus baicalensis'' Dybowski, 1874 - Baikal black grayling
* '' Thymallus brevipinnis'' Svetovidov ( ru), 1931 - Baikal white grayling
* '' Thymallus brevirostris'' Kessler, 1879 - Mongolian grayling
* '' Thymallus burejensis'' Antonov, 2004
* '' Thymallus flavomaculatus'' Knizhin, Antonov & Weiss, 2006 - yellow-spotted grayling
* '' Thymallus grubii'' Dybowski, 1869 - Amur grayling
*'' Thymallus mertensii'' Valenciennes, 1848
* '' Thymallus nigrescens'' Dorogostaisky, 1923 - Kosogol grayling
* '' Thymallus pallasii'' Valenciennes, 1848 - East Siberian grayling
* '' Thymallus svetovidovi'' Knizhin & Weiss, 2009 - Upper Yenisei grayling
* ''Thymallus thymallus'' (Linnaeus, 1758) - grayling
* '' Thymallus tugarinae'' Knizhin, Antonov, Safronov & Weiss, 2007 - Lower Amur grayling
* '' Thymallus yaluensis'' T. Mori, 1928

Modern reviewsWeiss, S. J., D. V. Gonçalves, G. Secci-Petretto, G. K. Englmaier, A. Gomes-Dos-Santos, G. P. J. Denys, H. Persat, A. Antonov, C. Hahn, E. B. Taylor and E. Froufe (2021) Global systematic diversity, range distributions, conservation and taxonomic assessments of graylings (Teleostei: Salmonidae; ''Thymallus'' spp.). ''Organisms Diversity & Evolution'': -18 (published online 25 Nov. 2020) and the ''Catalog of Fishes'' also list additional species including '' Thymallus nikolskyi'' , '' Thymallus baicalolenensis'' and '' Thymallus ligericus'' . 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''.Knizhin IB, Weiss SJ, Sushnik S (2006) Graylings of Baikal lake basin (''Thymallus'', Thymallidae): Diversity of forms and their taxonomic status. ''Journal of Ichthyology'' 46, 418-435.

References

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Extant Pleistocene first appearances
Ray-finned fish genera
Holarctic fauna