Steelhead Trout (Oncorhynchus mykiss)

What are Steelhead Trout?

Steelhead is a name for rainbow trout that are anadromous (Oncorhynchus mykiss). Anadromous means that the fish migrate from a freshwater river to the ocean, then back up the river to spawn. They are called “Steelhead” because they tend to acquire more silvery markings than other Rainbow trout. They generally live for 4-6 years. Their size is usually 20-30 inches long and about 8 pounds in weight, but some have been known to grow as long as 4 feet and as heavy as 53 pounds. Their color can vary, but they are generally silver in color with pinkish cheeks and green backs. For food,  they consume insects, crustaceans, and small fish. Though they are in the same family as salmon, they differ from them in migration timing, spawning timing, and reproductive strategies.

Where are Steelhead Trout?

Rainbow Trout are all over North America and vary depending on location. The Rainbow trout in and around the Cosumnes River are considered Steelhead Trout because they travel from the Cosumnes into the Mokelumne and into the Pacific Ocean. After spending a few years in the ocean, they travel back up the river. Their spawning locations can vary along the rivers, but they hatch in gravel-bottomed, fast-flowing rivers and streams. 

What do they eat?

For food,  they consume insects, crustaceans, and small fish.


Though not all Rainbow Trout are considered threatened, the Central Valley Steelhead Trout is severely impacted and listed as threatened under the Federal Endangered Species Act. Since these trout migrate long distances from the ocean up rivers, threats such as dams, development, diversions, urbanization, and other land use impact their numbers.

Male and female steelhead trout, photo provided by NOAA
Steelhead Trout, photo by Gary Riddle
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