ECOS Guide to the Ecology of the Northern Rockies

Name: Prosopium Williamsoni - Mountain Whitefish

Family: Salmonidae (Trout and Salmon)

Order: Salmoniformes (Salmon/Trout/Pike)

Class: Osteichthyes (Bony Fishes)

Abundance:

Origin: Native

Active Season: Year Round

Size:

Colors:

General Description: Adults 12” to 23”. Body slender and almost round in cross section. Color grayish blue above, silvery on side, and dull-whitish below. No black markings on sides, except in juveniles, which have a dozen or more black parr marks on sides. Mouth small and slightly inferior with no teeth. Adipose fin large.

Similar Species: This species is not easily confused with other species. In British Columbia and Alberta they can be confused with artic grayling (Thymalus arcticus) but this species does not co-occur with mountain whitefish in Montana (except in some parts of the upper Missouri River). In addition, arctic grayling have very large and colorful dorsal fins that distinguish them from mountain whitefish. It is the juvenile grayling, which have smaller dorsal fins, that can be confused with mountain whitefish.

Life History: Spawns in October through November. Hatchlings swim out of the gravel in March and can be found in side-channel habitat.

Usually becomes sexually mature in third year. Spawns near mouths of tributaries or in main channels of rivers over gravel. Over-winters in deep pools of larger rivers. Young hatch in March and move to side-channel habitat. Adults feed in tributaries and mainstems of rivers throughout the spring and summer. In September, mountain whitefish tend to have large prespawning aggregations before moving to spawning grounds in October (Northcote and Ennis 1994).

Distribution: Throughout northwest North America from Utah and Nevada north through British Columbia and Alberta. Widespread in larger rivers throughout the northern Rockies.

Habitat Description: Larger rivers

Feeding Habits: Feeds on bottom of rivers or from water column. Primarily feeds on benthic aquatic insects including mayfly nymphs, stonefly nymphs, caddisfly larvae, midge larvae, and black fly larvae (northcote and ennis 1994)

Did You Know: Some adults, called pinocchios, have really large and exaggerated snouts that they may use to feed by moving and pushing over rocks. In the early 1800’s, Lewis and Clark described a “bottlenosed” fish from Montana that might be the pinocchio form of the mountain whitefish. Mountain whitefish are one of the most common local fishes. A lot of people think that mountain whitefish compete with trout and make it so that fewer trout can live in rivers in the northern Rockies. There is no evidence to support this hypothesis. The only overlap that has been observed for the diet of mountain whitefish and trout is during the juvenile stage when they both eat a lot of midge (Chronomidae) larvae, which is not likely to be a limiting food source (A. Whiteley personal observation). During the Gold Rush, people used to catch mountain whitefish from the Bitterroot River and send them to Butte to feed the miners.

Adults can be found year round in the rivers around Missoula. In Missoula, the easiest time to see mountain whitefish is in Rattlesnake Creek from mid-October through late November (this is when they spawn). Look down from either of the footbridges in Greenough Park and look for their bluish/gray dorsal and caudal fins. Juveniles can be found in shallower portions of rivers throughout the year.

Glossary:

Adipose fin: a small fleshy fin along the midline of the back behind the dorsal fin.
Caudal fin: tail fin.
Dorsal fin: a fin along the midline of the back, usually midway between the head and tail fin.
Inferior mouth: mouth points down toward river or lake substrate.
Parr marks: dark vertical blotches on sides of juveniles.

Keywords: whitefish, salmonid, Prosopium, williamsoni

References:

Holton, G. D. and H. E. Johnson. 2003. A Field Guide to Montana Fishes, Third Edition. Montana Fish, Wildlife & Parks, Helena, MT.

Northcote, T. G. and G. L. Ennis. 1994. Mountain whitefish biology and habitat use in relation to compensation and improvement possibilities. Reviews in Fisheries Science. 24: 347-371.

Contributor:

Andrew Whiteley


Home Plant Guide Insect Guide Bird Guide Mammal Guide Geology Guide Fish Guide Fish by Name Fish by Family Fish by Order Glossary of Fish Terms Amphibian Guide Reptile Guide Habitats Descriptions Maps Contributors ECOS Home		Physical Characteristics - General Description - Similar Species - Life History - Distribution - Habitat - Feeding Habits - Did You Know - Glossary - References Name: Prosopium Williamsoni - Mountain Whitefish Family: Salmonidae (Trout and Salmon) Order: Salmoniformes (Salmon/Trout/Pike) Class: Osteichthyes (Bony Fishes) Abundance: Origin: Native Active Season: Year Round Size: Colors: General Description: Adults 12” to 23”. Body slender and almost round in cross section. Color grayish blue above, silvery on side, and dull-whitish below. No black markings on sides, except in juveniles, which have a dozen or more black parr marks on sides. Mouth small and slightly inferior with no teeth. Adipose fin large. Similar Species: This species is not easily confused with other species. In British Columbia and Alberta they can be confused with artic grayling (Thymalus arcticus) but this species does not co-occur with mountain whitefish in Montana (except in some parts of the upper Missouri River). In addition, arctic grayling have very large and colorful dorsal fins that distinguish them from mountain whitefish. It is the juvenile grayling, which have smaller dorsal fins, that can be confused with mountain whitefish. Life History: Spawns in October through November. Hatchlings swim out of the gravel in March and can be found in side-channel habitat. Usually becomes sexually mature in third year. Spawns near mouths of tributaries or in main channels of rivers over gravel. Over-winters in deep pools of larger rivers. Young hatch in March and move to side-channel habitat. Adults feed in tributaries and mainstems of rivers throughout the spring and summer. In September, mountain whitefish tend to have large prespawning aggregations before moving to spawning grounds in October (Northcote and Ennis 1994). Distribution: Throughout northwest North America from Utah and Nevada north through British Columbia and Alberta. Widespread in larger rivers throughout the northern Rockies. Habitat Description: Larger rivers Feeding Habits: Feeds on bottom of rivers or from water column. Primarily feeds on benthic aquatic insects including mayfly nymphs, stonefly nymphs, caddisfly larvae, midge larvae, and black fly larvae (northcote and ennis 1994) Did You Know: Some adults, called pinocchios, have really large and exaggerated snouts that they may use to feed by moving and pushing over rocks. In the early 1800’s, Lewis and Clark described a “bottlenosed” fish from Montana that might be the pinocchio form of the mountain whitefish. Mountain whitefish are one of the most common local fishes. A lot of people think that mountain whitefish compete with trout and make it so that fewer trout can live in rivers in the northern Rockies. There is no evidence to support this hypothesis. The only overlap that has been observed for the diet of mountain whitefish and trout is during the juvenile stage when they both eat a lot of midge (Chronomidae) larvae, which is not likely to be a limiting food source (A. Whiteley personal observation). During the Gold Rush, people used to catch mountain whitefish from the Bitterroot River and send them to Butte to feed the miners. Adults can be found year round in the rivers around Missoula. In Missoula, the easiest time to see mountain whitefish is in Rattlesnake Creek from mid-October through late November (this is when they spawn). Look down from either of the footbridges in Greenough Park and look for their bluish/gray dorsal and caudal fins. Juveniles can be found in shallower portions of rivers throughout the year. Glossary: Adipose fin: a small fleshy fin along the midline of the back behind the dorsal fin. Caudal fin: tail fin. Dorsal fin: a fin along the midline of the back, usually midway between the head and tail fin. Inferior mouth: mouth points down toward river or lake substrate. Parr marks: dark vertical blotches on sides of juveniles. Keywords: whitefish, salmonid, Prosopium, williamsoni References: Holton, G. D. and H. E. Johnson. 2003. A Field Guide to Montana Fishes, Third Edition. Montana Fish, Wildlife & Parks, Helena, MT. Northcote, T. G. and G. L. Ennis. 1994. Mountain whitefish biology and habitat use in relation to compensation and improvement possibilities. Reviews in Fisheries Science. 24: 347-371. Contributor: Andrew Whiteley