A steelhead at the Oregon Zoo. | Photo: cacophony/Wikimedia Commons/Creative Commons License Aquatic A Confusing, Compelling Wild Fish: Steelhead in the Delta

Steelhead, quite frankly, are confusing.

For one thing, they're rainbow trout. That's not a metaphor. Steelhead and rainbow trout are the same species: Oncorhynchus mykiss. In California waters, they're the same subpecies as the coastal rainbow trout, Oncorhynchus mykiss irideus. For some time it was assumed that close study would eventually reveal a significant genetic difference between rainbow trout and steelhead, because there's definitely a distinct behavioral difference between the two: steelhead spend much of their adult lives in the ocean, while rainbow trout stay in fresh water their whole lives.

LINK (via:KCET)