Prosopium Williamsoni



Freshwater Rivers, Lakes, Streams

3 - 5 pounds

10" - 28"

Mountain Whitefish

Also Known As: Rocky Mountain Whitefish, Mister White

Mountain Whitefish (Prosopium Williamsoni) Fish Description

This mountain whitefish is predominantly found in streams, but numbers have also been observed in reservoirs and lakes. Their population grows the most in clear and cold temperature rivers in the northwest area of North America, and usually co-habitat with trout.

Typically, this fish has a columnar shape with large scales and has a bronze-white or greenish-white color. Their needle-like snouts and narrow but rounded mouths make them competent in slurping up invertebrates and zooplankton from the bed’s bottom.


Interesting Facts About the Mountain Whitefish

  • Considered by some trout anglers as a “trash fish,” because they catch mountain whitefish instead of trout.
  • The Mountain Whitefish can reach up to 15,000 fish per mile in the Madison River. 
  • They can be cooked, smoked, or pickled.
  • It can live up to 18 years.


Mountain Whitefish Diet and Size

The mountain whitefish’s feeding peaks during the winter seasons, and consists mostly of bottom-dwelling aquatic insects. This carnivorous fish has been known to feed on terrestrial insects, smaller fish, and even fish eggs.

Mountain whitefish can weigh up to 5 pounds and grow to about 10-16 inches. While this small fish does not normally grow greater than 20 inches, the world record caught from the Columbia River in 1983, weighed 5 pounds and 2 ounces. 


Mountain Whitefish Habitat & Distribution 

The habitat range of the mountain whitefish stretches from the McKenzie River in Canada’s Northwest Territories to the Green River basin Utah. They can also be found in the drainages of some Pacific coastal rivers of British Columbia, and western Washington State. A highly adaptable fish, they have maintained large populations in streams and have shown a liking to gathering around hydroelectric reservoirs. These fish are generally not known to have constant migratory patterns. Instead, they may choose to only move to another part of a large river system or tributary streams to spawn. 

This species spawns in late October to November, assembling into highly populated groups that can engulf a whole streambed in certain spots. Mountain whitefish prefer colder streams with temperatures of 35-44 degrees Fahrenheit. The females let the eggs disperse onto the gravel substrate for fertilization, and by doing so, create a source of food for trout. The eggs will then hatch early to mid-March.


Mountain Whitefish Fishing Technique

Considered as a cold-water game fish, mountain whitefish are plentiful and are known to aggressively bite at the bait or take an artificial fly. The typical angler will probably not need to go and buy a special tackle - if you’re fishing for trout, most likely everything you need is at your disposal.

Since this fish has a small mouth, smaller hooks, flies, lures, and bait should be used accordingly. A mountain whitefish will nip at salmon eggs, worms or maggots. Anglers should try bobbing a maggot or salmon egg along the bottom with some split shot or pencil lead. Alternatively, fishing with a float suspending your bait near the bed’s bottom so it can move with the current is also recommended.

When fly fishing, weighted caddis, midge, and stonefly nymphs will work great to a slow or moderate current. Putting in some split shot can also help so that the flies drop to the bottom quicker. Since nymphing usually works with trout, you can expect some success with mountain whitefish as well. For larger rivers, you should use larger nymphs and for smaller bodies of water, sizes 14 to 16 would work best.