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

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...

of western North America. It is found from the Mackenzie River drainage in Northwest Territories, Canada south through western Canada and the northwestern USA in the Pacific, Hudson Bay and upper Missouri River basins to the

Truckee River The Truckee River is a river in the U.S. states of California and Nevada. The river flows northeasterly and is long.U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed October 20, 2012 Th ...

drainage in

Nevada Nevada ( ; ) is a state in the Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the 7th-most extensive, ...

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 Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

Description

The body shape is superficially similar to the

cyprinids Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest vert ...

, although it is distinguished by having the

adipose fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

salmonids 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 whit ...

. 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. The short

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

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 e ...

, 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 Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquat ...

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 A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastro ...

, crayfish, and

amphipods Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far describ ...

. 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 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, in the Columbia River, upper Missouri River, upper

Colorado River The Colorado River ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid watershed that encompasses parts of seven U.S. s ...

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 in

Idaho Idaho ( ) is a state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and Wyomi ...

, 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