To promote awareness of the animal, the Legislature adopted the state endemic mammal in 2009. 2009: Fish: Steelhead trout (Oncorhynchus mykiss) Adopted as the state fish in 1969, the steelhead is one of the most popular fish for recreational fishing in Washington. While the Legislature used an old scientific name Salmo gairdnerii to describe the fish, two subspecies of rainbow trout are anadromous and known as steelhead—Columbia River redband trout O. m. gairdneri and coastal rainbow trout O. m. irideus.