Overview
The Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi), proudly honored as the official state fish of Montana, is an iconic native salmonid that embodies the wild, unspoiled mountain waterways of the northern Rocky Mountains. Renowned for its brilliant crimson-red slash marks tucked beneath each side of its lower jaw, this magnificent native trout is a sensitive ecological barometer, thriving only in the coldest, cleanest, and most oxygen-rich headwater streams.
Biology and Physical Characteristics
Oncorhynchus clarkii lewisi is characterized by a sleek, hydrodynamic body adorned with a distinctive spotting pattern: small, irregularly shaped black spots are concentrated heavily on the caudal peduncle and dorsal area behind the dorsal fin, leaving the front half of its flank relatively unspotted. Its flank coloration ranges from iridescent silvery-olive to bright coppery-bronze, turning deep golden-yellow with bright reddish hues along the belly during the spring spawning season.
Behavior and Ecology
Highly specialized for cold, high-gradient mountain streams, the Westslope Cutthroat feeds primarily on drifting aquatic insect larvae and terrestrial insects that fall onto the water surface. In spring, as snowmelt peaks, mature adults migrate upstream into tiny headwater tributaries, where females excavate shallow gravel nests (redds) to deposit their eggs. Stream forms remain resident, while adfluvial forms migrate down into large lakes to mature.
Conservation and Human Impact
Historically widespread, the Westslope Cutthroat has declined across more than 70% of its native range due to habitat degradation from logging, mining, and road construction, combined with hybridization with non-native rainbow trout and competition from introduced brook trout. Strict catch-and-release fly fishing regulations and genetic barrier projects now protect pure native strains.
Interesting Factoid
The Westslope Cutthroat Trout was the very first trout species formally recorded by the Lewis and Clark Expedition in 1805 near Great Falls, Montana, which is why its scientific subspecific name ‘lewisi’ honors explorer Meriwether Lewis.