Prosopium williamsoni (Girard, 1856)
Mountain whitefish
Prosopium williamsoni
photo by Keeley, E.R.

Family:  Salmonidae (Salmonids), subfamily: Coregoninae
Max. size:  70 cm TL (male/unsexed); max.weight: 2,920.0 g; max. reported age: 17 years
Environment:  benthopelagic; freshwater; depth range 5 - 20 m
Distribution:  North America: Mackenzie River drainage in Northwest Territory, Canada south through western Canada and northwestern USA in the Pacific, Hudson Bay and upper Missouri River basins to Truckee River drainage in Nevada and Sevier River drainage in Utah, USA.
Diagnosis:  Dorsal spines (total): 0-0; Dorsal soft rays (total): 11-15; Anal spines: 0-0; Anal soft rays: 10-13; Vertebrae: 53-61. Body slender, elongate, nearly cylindrical in cross section but variable, more compressed laterally than round whitefish. Head short; eye moderate, its diameter less than snout length; snout more or less pointed, compressed laterally, pinched, rounded in lateral view, a single flap of skin present between nostrils. Mouth small, ventral in position, overhung by snout; maxillaries extending posteriorly almost to anterior margin of eye in adults. Teeth small, restricted to a small patch on tongue and on gill rakers in adults, although small teeth may be present on the premaxillaries in young, but absent from jaws, vomer, palatines and pre maxillae in adults. Overall coloration silvery, but light or dark brown or olive on back, becoming silvery in sides and white below. Scales, specially on back, may have pigmented borders. dorsal fin often dusky, pelvic and pectoral fins in adults with amber tint.
Biology:  Occurs in lakes and fast, clear or silty streams. Feeds mainly on benthic organisms such as aquatic insect larvae, mollusks, fishes, and fish eggs (including their own) but may feed on plankton and surface insects when the need arises (Ref. 1998).
IUCN Red List Status: Not Evaluated (N.E.) Ref. (124695)
Threat to humans:  harmless
Country info:   

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