Montana offers diverse aquatic environments, ranging from cold, turbulent mountain streams in the west to vast, slow-moving prairie rivers and reservoirs in the east. This extensive network supports a wide array of fish species, each adapted to its unique habitat.
Iconic Coldwater Game Fish
The cold, clear rivers of Western Montana are known for their salmonid populations, which thrive in clean, oxygen-rich waters that remain consistently cool. The native Cutthroat Trout is distinguishable by the red or orange slash mark beneath its lower jaw and is found in two main subspecies: the Westslope and the Yellowstone Cutthroat.
The non-native Rainbow Trout, introduced from the Pacific Northwest, is popular among anglers for its aggressive fight. Rainbows are identified by a prominent pink or reddish stripe along the lateral line, contrasting with a heavily spotted body. Both Cutthroat and Rainbow trout are spring spawners.
Brown Trout, introduced from Europe, are fall spawners, allowing their young to hatch earlier. They are found in larger, slower sections of rivers and lakes, identifiable by their yellowish-brown body with large, dark spots often surrounded by a pale halo. Brook Trout, technically a char, also spawn in the fall and prefer the coldest, highest-elevation waters. They possess a dark body with light, worm-like markings on their back and dorsal fin, along with white-edged lower fins.
Warmwater Species of the Plains and Reservoirs
East of the Continental Divide, the landscape flattens into prairie, and the rivers widen, forming large reservoirs. These waters are generally warmer and more turbid than trout streams, creating ideal conditions for cool- and warmwater species like Walleye. Walleye are popular in large impoundments like Fort Peck and Tiber Reservoirs.
Walleye are a non-native coolwater species that flourish in the open water of large reservoirs and rivers like the Missouri and Yellowstone. They are characterized by large, opaque eyes that allow them to feed effectively in low-light conditions. Northern Pike are also abundant, particularly in the shallow, weedy bays of reservoirs, where they act as top predators.
The Northern Pike is recognizable by its long, slender body and duck-bill snout filled with sharp teeth. Smallmouth Bass inhabit rocky areas near the shorelines of reservoirs, often coexisting with pike and walleye. The Channel Catfish, a bottom-dwelling fish, is found in the large, warm prairie rivers, known for its smooth skin and whisker-like barbels around the mouth.
Native Status and Conservation Concerns
The ecological health of Montana’s aquatic systems is defined by the distinction between its native fish species and those that have been introduced, primarily for sport fishing. Native species like the Westslope Cutthroat Trout and the Pallid Sturgeon face serious conservation challenges. Habitat loss has severely restricted the range of the Westslope Cutthroat, which now occupies less than 10% of its historical habitat due to barriers like dams and the dewatering of streams for irrigation.
The genetic integrity of the native Cutthroat is threatened by hybridization with non-native Rainbow Trout. Introduced species like Brook Trout and Brown Trout actively compete with native trout for food and habitat. Brook Trout often outcompete juvenile Cutthroat in smaller headwater streams.
The Pallid Sturgeon is listed as a federally endangered species. This fish inhabits the turbid, bottom sections of the Missouri and Yellowstone rivers, where its survival is hampered by river channelization and the lack of natural flow regimes. Conservation efforts focus on managing water flow and implementing projects like the Intake Bypass on the Yellowstone River, which helps native species migrate to upstream spawning grounds.
Essential Non-Game Fish and Aquatic Life
While not the targets of most anglers, non-game fish species support Montana’s aquatic food web. Suckers, including the Longnose and White Sucker, are a ubiquitous component of both cold and warm water ecosystems. These bottom-feeding fish convert algae and aquatic insects into protein, making them a significant forage base for larger predatory fish like trout and pike.
Other small species, such as minnows, dace, and sculpins, fill the role of primary forage. Sculpins are small, bottom-dwelling fish with large heads, often found hiding under rocks in cold streams. They are a substantial part of the diet for Bull Trout.