Salmonidae
Mountain whitefish
Prosopium williamsoni · 25–45 cm, rarely over 50 cm.
How it feeds
Mountain whitefish are bottom feeders with a subterminal mouth, built for picking aquatic insect larvae and small crustaceans off gravel. They shoal in the deeper tailouts and are the first fish to react when a heavy nymph drift is on the bottom.
How to fish for it
Often dismissed as a nuisance, whitefish are a useful signal: if you are catching them consistently on the bottom, your nymph depth is right and the trout will be in the same seam, slightly higher in the water column.
Flies that work: Pheasant Tail Nymph · Hare's Ear Nymph · Zebra Midge · Prince Nymph
Mountain whitefish in the ledger
Bighorn River
South-central Montana, United StatesA cold, stable tailwater with 3,000+ fish per kilometre and midge hatches in January.
brown · rainbow · whitefish
Mar · Apr · Sep · Oct · Nov · DecMadison River
Southwest Montana, United StatesA 183 km riffle-and-run river where dam releases, not rain, decide your fly.
brown · rainbow · whitefish
Apr · May · Jun · Sep · OctYellowstone River
Montana and Wyoming, United StatesThe longest free-flowing river in the lower 48, and the best native cutthroat fishery in it.
cutthroat · rainbow · whitefish
Jul · Aug · Sep · Oct