The classification of steelhead often causes confusion, as it shares characteristics and behaviors with both trout and salmon. Understanding its biological identity and the general distinctions between trout and salmon species can clarify this question.
Steelhead’s Biological Identity
A steelhead is a rainbow trout (Oncorhynchus mykiss). The term “steelhead” specifically refers to the anadromous, or sea-run, form of this species. While some rainbow trout spend their entire lives in freshwater, steelhead migrate to the ocean for growth before returning to freshwater to spawn. This migratory behavior is the primary difference between a steelhead and a resident rainbow trout, not a genetic distinction.
Distinguishing Characteristics of Trout and Salmon
Trout and salmon belong to the same family, Salmonidae, but exhibit general differences in their life histories and physical traits. Salmon species, particularly Pacific salmon (Oncorhynchus genus), are larger and more robust than most trout. Many salmon are semelparous, spawning once and then dying. Atlantic salmon (Salmo salar) and some trout species, however, can be iteroparous, capable of spawning multiple times throughout their lives.
Trout species, such as those in the Salmo and Salvelinus genera, generally remain in freshwater, though some populations can be anadromous. Salmon begin their lives in freshwater, migrate to the ocean to mature, and then return to their natal freshwater streams to reproduce. While both groups prefer cold, clear waters, their typical habitats differ significantly during their adult phases. Salmon also develop distinct color changes and physical alterations, like hooked jaws in males, during their spawning migrations.
The Anadromous Steelhead
The steelhead’s life cycle closely mirrors many salmon species, contributing to classification confusion. They hatch in freshwater streams, spending 1 to 3 years there. After this juvenile phase, they transform into “smolts,” enabling saltwater survival. Smolts then migrate to the ocean, growing significantly over one to five years.
Upon maturity, steelhead return to natal freshwater streams to spawn, a migratory pattern characteristic of salmon. This journey often involves navigating hundreds of miles upstream. Unlike most Pacific salmon, steelhead are iteroparous; they can survive spawning and return to the ocean to spawn again. This ability to undertake multiple spawning migrations distinguishes steelhead from many salmon, despite similar anadromous behaviors.