The Arctic grayling (Thymallus arcticus) is a species of freshwater fish in the salmon family (family Salmonidae) of order Salmoniformes. It comprises five subspecies, including the Arctic grayling proper (T. arcticus arcticus).
It is native to the Nearctic (one of the eight terrestrial ecozones dividing the Earth’s land surface) and Palearctic ecozones, T. arcticus arcticus being widespread throughout the Arctic and Pacific drainages in Canada, Alaska, and Siberia, as well as the upper Mississippi River draining in Montana, and formerly in the Great Lakes region, where it has become extinct. Other subspecies have narrower ranges, T. arcticus baicalensis, for example, being restricted to Lake Baikal and its drainage in Russia and T. arcticus grubii to the Amur basin in East Asia.
T. arcticus arcticus grows to a maximum recorded length of 30 in (76 cm) and a maximum recorded weight of 8.4 lb (3.8 kg); the other subspecies range in maximum length from 12″“17 in (30 to 44 cm), with maximum weights as low as one-third that of the Arctic grayling proper. Of typical Thymallus appearance, the Arctic grayling is distinguished from the similar grayling (T. thymallus) by the absence of dorsal and anal spines and the presence of a larger number of soft rays in these fins. There is a dark longitudinal line between the pectoral and pelvic fins, and the flanks may possess a pink iridescence. Some subspecies exhibit distinctive coloration, T. arcticus baicalensis, for example, being darker in color with two wide vertical bars of lighter shade along its body. T. arcticus arcticus has been recorded as reaching an age of 18 years.
Arctic graylings occur principally in cold waters of mid-sized to large rivers and lakes, returning to rocky streams to breed, although T. arcticus baicalensis remains in shallow waters for its entire life. The various subspecies are omnivorous; crustaceans, insects, and fish eggs and larvae forming the most important food items; larger T. arcticus arcticus individuals feed on adult fish and even small aquatic mammals, such as lemmings, while the immature fish feed on zooplankton, including insect larvae.
Spawning takes place in the spring, when the fish seek the shallow areas of rivers with fine sand substrate and moderate current. The males then establish individual territories and court the females by flashing their colorful dorsal fins; the fins are also used to brace receptive females during the vibratory release of milt and roe. As these fishes are nonguarders, the eggs are left to mix with the substrate. Although the graylings do not excavate nests, the highly energetic courtship and mating tends to kick up silt and cover the eggs. The eggs are small (approximately 3 mm in diameter) and hatch after two to three weeks. The hatched larvae remain in the substrate until they reach a length of around 0.5″“0.7 in (12″“18 mm), at which time they form shoals at the river margins. The fry grow quickly during their first year or two of life.
With the grayling proper (T. thymallus), the T. arcticus arcticus is one of the economically important Thymallus species, being raised commercially and fished for sport.
The Arctic grayling is sensitive to pollution and has disappeared from the North American Great Lakes, but since it remains widespread elsewhere it is not listed on the IUCN Red List of threatened species.
Obsolete synonyms for T. arcticus arcticus include T. montanus, T. signifer, and T. tricolor. The species is also known as the Alaska grayling.
Several submarines and patrol boats of the United States Navy have been named USS Grayling after this species.