Pick Our Brain - August 2010

What is the difference between a steelhead and a rainbow trout?

A steelhead is an anadromous rainbow trout, that is, one that migrates from freshwater to the ocean and back. The rainbow trout, Oncorhynchus mykiss, is one of the most widely distributed and common freshwater fish in California and it has been introduced to cold fresh waters all over the world. The anadromous variety (steelhead) in many parts of California, however, is considered threatened.

Steelhead behave like salmon, maturing in the ocean and returning to their home streams to spawn. Unlike salmon, however, steelhead may spawn more than once and spend varying amounts of time in freshwater and the ocean. Many do not leave their home streams at all but become “resident” rainbow trout. In the Central Valley fewer and fewer are managing to find their way to the ocean and back. Many Central Valley rivers and streams with access to the sea have abundant rainbow trout populations but few migrate to the ocean to become steelhead. They seem to be shifting to a “resident” life history strategy, presumably finding more success staying in freshwater. The exact genetic and environmental factors that cause a rainbow trout to go to sea and become a steelhead are not completely understood and are the subject of ongoing research.

One characteristic of steelhead vs. resident rainbow trout is their larger size. Resident rainbow trout in most streams rarely exceed 15 inches in length while steelhead from the same stream can reach 30 inches or more. Steelhead fresh from the ocean are usually silvery with bluish gray backs and heads-this is thought to be the source of their common name. Their large size and legendary fighting ability make them one of the state’s most sought after sport fish. Steelhead are sometimes called “the fish of a thousand casts” because of the effort it sometimes takes to catch one.

Rainbow Trout
Rainbow Trout
Steelhead
Steelhead