Mountain whitefish (Prosopium)
Mountain whitefish have a wide range of coloration, from brown to copper-gold or greenish to blue-gray on the back and sides. The sides can also be completely silver, and the belly is either silver or white. They have no spots or lines on their body, which is covered with large and coarse scales.
The snout and lower jaw are short and blunt, and the head is small relative to its elongate and cylindrical body. The caudal, or tail, fin is deeply forked.
Mountain whitefish travel mostly in schools and are primarily bottom feeders. A major part of their diet consists of aquatic insect larvae, especially the larvae of the caddisfly, mayfly, stonefly and midge. Occasionally, they will also feed on beetles, ants, mollusks and small fish.
In the fall spawning season, they heavily consume their own eggs. During the spawning season of trout, they will also eat their eggs.
Mountain whitefish are native to lakes and streams in the Pacific Northwest, ranging from the northwestern United States to southwestern Canada. Their southern boundary is the Lahontan basin in Nevada and the range extends north to the southern edge of the Yukon Territory. Populations also occur in Alberta, Canada, as well as Wyoming in the U.S.
Mountain whitefish are found in mountain lakes, rivers and streams, preferring moderate to large rivers with fast flowing water, deep pools and gravel bottoms. The ideal temperature range for mountain whitefish is between 48 and 52 F, but they can withstand temperatures far above and below this range, which gives them greater survival abilities than trout or salmon in harsh weather extremes. They are also able to thrive in water with lower dissolved oxygen levels.
During summers, stream-dwelling mountain whitefish are found in riffle areas, but in winter they congregate in the larger pools. In lakes, they are usually found in shallow water through most of the year, unless high water temperatures (55 F or above) force the fish to deep water, usually 30 feet or less.
- The species name, williamsoni, is taken after Lieutenant R.S. Williamson of the U.S. Pacific Railroad Exploration.
- A close relative of mountain whitefish is the lake whitefish, found chiefly in the Great Lakes. Lake whitefish are larger than mountain whitefish and are considered an important food fish in those areas.