Oncorhynchus mykiss irideus
Coastal rainbow trout/steelhead (Oncorhynchus mykiss irideus) In North America, coastal rainbow trout are native to Pacific coast streams, from the Kuskokwim River in Alaska south to Baja California. In California, coastal rainbow trout are the most widely-distributed native trout form and are found on the western slopes of the Sierra Nevada in waters draining to the Pacific Ocean. Widespread glaciation that occurred over 10,000 years ago likely limited coastal rainbow trout distribution to elevations less than 8,000 feet on the west slope of the Sierra Nevada (probably lower elevations in the northern part of the range). Source: California Dept. Fish and Game
Steelhead trout is a name given to the anadromous form of the coastal rainbow trout (Oncorhynchus. m. irideus) or redband trout (O. m. gairdneri). The steelhead are native to freshwater and ocean environments across North America, but have been introduced to every other continent except Antarctica. The freshwater form of the steelhead trout is the rainbow trout. The difference between these forms of the species is that steelhead migrate to the ocean and return to freshwater tributaries to spawn, whereas rainbow trout do not leave freshwater. Steelhead are also larger and less colorful than rainbow trout. Steelhead can weigh up to 55 pounds (26 kg) and reach 45 inches (114 cm) in length. They can live up to 11 years and spawn multiple times. The body of the steelhead trout is silvery and streamlined with a rounder head. There are black dots and a red or pink stripe running down the side of the fish horizontally. This silver color and round head is what gives the steelhead its name.
Note: also see Coastal Steelhead