About Thymallus arcticus (Pallas, 1776)
Arctic grayling (Thymallus arcticus (Pallas, 1776)) grow to a maximum recorded length of 76 cm (30 in) and a maximum recorded weight of 3.8 kg (8.4 lb). They have the typical appearance of thymalline fish, and can be distinguished from the similar European grayling (T. thymallus) by the lack of dorsal and anal spines, and by having a larger number of soft rays in these two fins. A dark midlateral band runs between the pectoral and pelvic fins, and the flanks may show a pink iridescence. The nominate subspecies T. a. arcticus has been recorded to reach an age of 18 years. Arctic grayling are widespread across Arctic Ocean drainages, ranging from Hudson Bay, Canada to Alaska, and also occur in Arctic and Pacific drainages extending to central Alberta and British Columbia in Canada. They do not occur naturally in the Fraser and Columbia river basins. Remnant native populations of fluvial Arctic grayling exist in the upper Missouri River drainage, specifically in the Big Hole River and Red Rock basin (the "Montana Arctic grayling"). Fluvial Arctic grayling have been reestablished in the upper Ruby River, a tributary of the Beaverhead River. The species' native range once extended south into the Great Lakes basin in Michigan, where it was extirpated by 1936 due to habitat destruction, unregulated logging, and competition from non-native fish species. Arctic grayling occurs naturally in the Arctic Ocean basin in Siberia from the Ob to Yenisei drainages, and in European Russia in some tributaries of the Pechora river. Lake-dwelling forms of Arctic grayling have been introduced to suitable lake habitats throughout the Rocky Mountains, including lakes in Wyoming's Teton Range, central Idaho, Utah's high Uinta Mountains, the Cascade Mountains, and the Sierra Nevada Mountains as far south as Arizona. There are three main life history forms of Arctic grayling: fluvial populations that live and spawn in rivers; lacustrine populations that live and spawn in lakes; and potamodromous populations that live in lakes and spawn in tributary streams. Arctic grayling live primarily in the cold waters of mid-sized to large rivers and lakes, and return to rocky streams to breed. The various subspecies are omnivorous. Crustaceans, insects and insect larvae, and fish eggs make up the most important food items. Larger T. arcticus specimens become piscivorous, while immature fish feed on zooplankton and insect larvae. Spawning occurs in spring. Adult fish seek out shallow areas of rivers with fine, sand substrate and moderate current. Males are territorial and court females by flashing their colourful dorsal fins; these fins are also used to brace receptive females during the vibratory release of milt and roe. Arctic grayling do not guard their eggs, which are left to mix with the substrate. While the fish do not excavate a nest, the highly energetic courtship and mating process tends to kick up fine material that covers the zygotes. Zygotes are small, measuring approximately 3 mm (0.1 in) in diameter, and embryos hatch after two to three weeks. Newly hatched embryos remain in the substrate until all their yolk is absorbed. They emerge at a length of around 12 to 18 mm (0.5 to 0.7 in), at which point they form shoals along river margins. Juveniles grow quickly during their first two years of life.
