Rainbow Trout

The rainbow trout (Oncorhynchus mykiss), a species of trout, is native to tributaries of the Pacific Ocean in Asia and North America. Rainbow trout subspecies native to the western states include:

• Coastal rainbow trout (O. m. irideus),

• Eagle Lake trout (O. m. aquilarum), and

• Redband trout (O. m. gairdneri, O. m. newberrii, O. m. stonei).

The species historically included trout of the Gila and Apache trout and the golden trout. These are covered separately in this series of articles.

Steelhead

Sea-run (anadromous) forms of rainbow trout are commonly called steelhead.

Steelhead, like Salmon, spawn in freshwater streams. The smolts run to the sea where they live until they subsequently return to spawn. Steelhead typically spend 15–30 months in the ocean before spawning. Though steelhead can spawn multiple times, most steelhead do not survive the hardships of the migration and spawning. The survival rate is estimated to be 10–20%.

Steelhead can weigh over 30 lbs (15 kg) and reach over 40 inches in length.

The name refers to the silver-colored body of steelhead when they return from the ocean. Steelhead develop a pink stripe along their lateral line. As they spend more time in freshwater they will take on colors of their resident forms of their subspecies.

Steelhead populations are generally imperiled. The southern California population is critically imperiled.

Winter and Summer Steelhead

Winter steelhead migrate to their freshwater spawning grounds during the winter and early spring months. Summer steelhead migrate during late spring, summer and fall. 

Winter steelhead mature in the ocean before migrating to their freshwater spawning grounds. Winter steelhead may spawn within a few days of entering freshwater and return shortly afterwards. Summer steelhead start their migration before they are fully mature, often while still juveniles. They will spend up to a year in freshwater before spawning.

Winter steelhead may feed very little or not at all on their migration. Summer steelhead must continue to forage for food to complete their maturation.  Summer steelhead are often eager to chase baitfish and dine on aquatic insects.

Trout of the World

Rainbow trout are well renowned and widely sought after sport fish. Rainbow trout have been widely introduced to lakes and streams worldwide. Where introduced, they have often negatively impact native species, whether by preying upon native species, outcompeting them, and hybridizing with closely related species or across subspecies. They may also transmit contagious diseases or parasites. They are regarded as one of the most invasive alien species on the planet.

Additional Reading

• Trout and Salmon of North America by Robert Behnke