The mountain whitefish (''Prosopium williamsoni'') is one of the most widely distributed

salmonid Salmonidae is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whitefis ...

fish of western

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. It is found from the Mackenzie River drainage in

Northwest Territories The Northwest Territories (abbreviated ''NT'' or ''NWT''; french: Territoires du Nord-Ouest, formerly ''North-Western Territory'' and ''North-West Territories'' and namely shortened as ''Northwest Territory'') is a federal territory of Canada. ...

, Canada south through western Canada and the northwestern USA in the Pacific, Hudson Bay and upper Missouri River basins to the Truckee River drainage in Nevada and

Sevier River The Sevier River (pronounced "severe") is a -long river in the Great Basin of southwestern Utah in the United States. Originating west of Bryce Canyon National Park, the river flows north through a chain of high farming valleys and steep canyons ...

drainage in Utah.

Description

The body shape is superficially similar to the cyprinids, although it is distinguished by having the adipose fin of salmonids. The body is slender and nearly cylindrical in cross section, generally silver with a dusky olive-green shade dorsally. The scales possess pigmented borders, which are especially defined on the posterior end. Mountain Whitefish possess a forked homocercal tail. The short head has a small mouth underneath the

snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...

. The short dorsal fin has 12–13 rays, with 11–13 for the anal fin, 10–12 for the

pelvic fins Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two en ...

, and 14–18 for the pectoral fins. Size has been recorded at up to 70 centimeters (28 inches) in length and a weight of 2.9 kilograms (6.4lb).

Life History

The spawning season is from October to early December, when water temperatures are 2–6 °C. Mountain whitefish congregate in large schools on fall spawning runs and seek out areas of coarse gravels or cobbles at depths of at least 75 cm (30 inches), typically in shallow areas of small tributaries or shorelines of lakes. Their non-adhesive eggs are scattered along the substrate. The eggs then develop slowly through the winter (6–10 weeks), hatching in the early spring, generally in March. Mountain whitefish reach reproductive maturity at approximately three years old, females can produce as many as 4,000 eggs annually. Mountain whitefish typically live between 7–9 years in the wild.

Feeding

Mountain Whitefish are demersal feeders, stirring up the substrate with pectoral and tail fins to expose insect larvae and other invertebrates, including snails,

crayfish Crayfish are freshwater crustaceans belonging to the clade Astacidea, which also contains lobsters. In some locations, they are also known as crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, mu ...

, and amphipods. Their main feeding time is in the evening, but they will also take drifting prey during the day. The mountain whitefish frequently feeds in the lower strata of streams, but populations may rise to the surface to prey on hatching insects, including mayflies. Mountain whitefish fry are a common food source for brook trout.

Ecology

Habitat

The mountain whitefish are commonly found in mountain streams and lakes, favoring clear cold water and large deep pools of at least a meter's depth; the

Lake Tahoe Lake Tahoe (; was, Dáʔaw, meaning "the lake") is a Fresh water, freshwater lake in the Sierra Nevada (U.S.), Sierra Nevada of the United States. Lying at , it straddles the state line between California and Nevada, west of Carson City, Nevad ...

population lives just above the bottom in deeper water.

Range

This species occurs throughout the western half of North America, as far north as the Mackenzie River (Canada) and the drainages of the

Hudson Bay Hudson Bay ( crj, text=ᐐᓂᐯᒄ, translit=Wînipekw; crl, text=ᐐᓂᐹᒄ, translit=Wînipâkw; iu, text=ᑲᖏᖅᓱᐊᓗᒃ ᐃᓗᐊ, translit=Kangiqsualuk ilua or iu, text=ᑕᓯᐅᔭᕐᔪᐊᖅ, translit=Tasiujarjuaq; french: b ...

, in the

Columbia River The Columbia River (Upper Chinook: ' or '; Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, C ...

, upper Missouri River, upper Colorado River.

Conservation

Mountain Whitefish have a secure conservation status. In many of the larger intermountain Western rivers, Mountain Whitefish are the only native salmonid. Mountain whitefish typically occur in high abundance, in the

Snake River Basin The Snake River cutting through the plain leaves many canyons and Canyon#List of gorges">gorges, such as this one near Twin Falls, Idaho The Snake River Plain is a geologic feature located primarily within the U.S. state of Idaho. It stret ...

in Idaho, Mountain Whitefish abundance was found to be 1,257/100 m.

References

{{Taxonbar, from=Q2111461 Prosopium Freshwater fish of the United States Fish of Canada Fish of the Western United States Fauna of the Northwestern United States Fauna of California Fauna of the Great Basin Fauna of the Rocky Mountains Taxa named by Charles Frédéric Girard Fish described in 1856