Oncorhynchus mykiss
Populations of many rainbow trout subspecies, including anadromous forms (steelhead) of (coastal rainbow trout) and (Columbia River redband trout) have declined in their native ranges due to over-harvest, habitat loss, disease, invasive species, pollution and hybridization with other subspecies, and some introduced populations, once healthy, have declined for the same reasons. As a consequence, some rainbow populations, particularly anadromous forms within their native range, have been classified as endangered, threatened or species of special concern by federal or state agencies. Rainbow trout, and subspecies thereof, are currently a U.S. Environmental Protection Agency-approved indicator species for acute fresh water toxicity testing.