Westslope Cutthroat Trout

Oncorhynchus clarkii lewisi

The westslope cutthroat trout (Oncorhynchus clarkii lewisi) is a subspecies of cutthroat trout in the family Salmonidae. Adults typically reach 25-45 cm with a streamlined body displaying olive-green to yellowish-brown coloration above, silvery sides with prominent dark spots concentrated toward the tail, and distinctive red-orange slash marks under the lower jaw that give the species its name. This fish inhabits cold, clear mountain streams, rivers, and lakes at elevations up to 3,000 meters across the northern Rocky Mountains, from Montana and Idaho to British Columbia. They require pristine, cold-water habitats with temperatures below 15C. Westslope cutthroat feed on aquatic insects, crustaceans, and smaller fish. Named from specimens collected during the Lewis and Clark Expedition, they face conservation challenges from hybridization with introduced rainbow trout and habitat degradation. Encountering them in clear mountain streams is a testament to healthy watershed conditions.