Rainbow Trout: where and when to see them

Rainbow trout are freshwater fish in the salmon family, native to rivers and lakes draining into the North Pacific. They occur naturally in the Columbia River Basin, where both freshwater-resident rainbow trout and sea-run steelhead belong to this species. Steelhead migrate to the ocean to feed and grow before returning to freshwater to reproduce. Rainbow trout have also been introduced widely beyond their native range. Despite their broad global distribution, some native Columbia Basin populations face serious pressures from habitat degradation, warming water and barriers to migration.

Size

Typically 30–60 cm long as an adult; sea-run steelhead can exceed 1 m.

Weight

Many adults weigh about 0.5–4 kg; large steelhead can exceed 10 kg.

Lifespan

Typically 4–6 years, although some individuals live longer.

Status

Least Concern globally; some Columbia Basin steelhead populations are federally listed as threatened or endangered.

Rainbow trout often hold position in flowing water, using cover or slower currents while watching for drifting food. They make short movements into faster water to intercept prey. Larger fish may defend profitable feeding positions, while smaller individuals sometimes gather in loose groups. Activity varies with water temperature, light and food availability. Resident fish may move between tributaries, larger rivers and lakes as conditions change. Steelhead undertake much longer migrations between freshwater and the ocean. Spawning generally occurs in late winter or spring, with timing varying among populations, and females excavate gravel nests called redds. Unlike Pacific salmon in the genus Oncorhynchus, which generally die after spawning, rainbow trout and steelhead can survive and spawn again.

• Rainbow trout and steelhead are the same species with different life histories.
• Females dig their gravel spawning nests using movements of the tail.
• Young rainbow trout have dark vertical markings called parr marks.
• Some steelhead survive spawning and return to the ocean to feed again.

Wildlife opportunities depend on the river reach, water levels and species. River-specific viewing months have not been confirmed; general species seasons are not a local sighting forecast.

Rainbow trout favor cool, well-oxygenated freshwater with access to feeding areas, shelter and suitable spawning gravel. In the Columbia Basin, they occupy tributary streams, larger river reaches, lakes and reservoirs. Pools, riffles, submerged wood and rocky margins provide different feeding and refuge opportunities. During warm periods, cold tributaries and groundwater-fed areas can become especially important refuges. Steelhead also require connected migration routes between inland spawning grounds and the Pacific Ocean.

Rainbow trout eat aquatic insects, including the larvae and nymphs of mayflies, caddisflies and stoneflies. They also take insects that fall onto the water, along with crustaceans, fish eggs and other available prey. Larger individuals often consume small fish. Steelhead feeding at sea eat fish, squid and crustaceans.

Common name

Rainbow Trout

Scientific name

Oncorhynchus mykiss

Animal group

Fish

Size

Typically 30–60 cm long as an adult; sea-run steelhead can exceed 1 m.

Weight

Many adults weigh about 0.5–4 kg; large steelhead can exceed 10 kg.

Lifespan

Typically 4–6 years, although some individuals live longer.

Status

Least Concern globally; some Columbia Basin steelhead populations are federally listed as threatened or endangered.

Identification

Resident rainbow trout usually have a greenish or bluish back, silvery sides and a pink to reddish stripe along each flank. Small black spots cover the back, dorsal fin and much of the tail. Steelhead at sea or newly returned to rivers are often bright silver, with a faint or inconspicuous pink stripe. Color varies with habitat, age and breeding condition, so a distant surface glimpse rarely allows confident identification.