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Mountain Whitefish Prosopium williamsoni


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Mountain Whitefish
credit: Woostermike

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Family: Salmonidae, Trouts view all from this family

Description The mountain whitefish Prosopium williamsoni is one of the most widely distributed salmonid fish of western North America. Body is slender and nearly cylindrical in cross section, generally silver with a dusky olive green shade dorsally. The short head has a small mouth underneath the snout. The short dorsal fin has 12-13 rays, with 11-13 for the anal fin, 10-12 for the pelvic fins, and 14-18 for the pectoral fins. The tail fin is forked. Size has been recorded at up to 70 cm in length and a weight of 2.9 kg.

It is a fish of mountain streams and lakes, favoring clear cold water and large deep pools of at least a meter depth; the Lake Tahoe population lives just above the bottom in deeper water. Mountain whitefish are bottom feeders, stirring up the substrate with pectoral and tail fins to expose insect larvae and other invertebrates, including snails, crayfish, 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.

Dimensions Up to 28" (70 cm).

Habitat Rivers & streams, Lakes & ponds.

Range 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, and so forth.

Discussion Although once important in the subsistence fisheries of some Native American peoples, this species has become less available in modern times, possibly due to overharvesting; as of 2002 detailed surveys had not been conducted. Some sportfishing for mountain whitefish occurs. Anglers commonly capture whitefish with small (size 16 to 22) nymphs such as Pheasant Tail, Hare's Ear, and Disco Midge. The fish will also respond to tiny spinners, streamers, and dry flies.