McCloud River redband trout

The McCloud River redband trout (Oncorhynchus mykiss stonei) is one of three redband trout subspecies of the rainbow trout in the family Salmonidae. The trout is native in small tributaries of the McCloud River and Pit River which are tributaries of California's Sacramento River. Its historic range has declined significantly since it was first described in 1894. Remaining populations of genetically pure McCloud River redband trout are threatened by predation, habitat loss, competition with introduced trout species and by hybridization with hatchery rainbow trout introduced to support sport fishing.

Historic influence on hatchery rainbow trout
In 1877, the second California rainbow trout hatchery and the first federal fish hatchery in the National Fish Hatchery System, was established on Campbell Creek, a McCloud River tributary. The McCloud River hatchery indiscriminately mixed coastal rainbow trout (O. m. irideus) eggs with the eggs of local McCloud River redband trout (O. m. stonei). Eggs from the McCloud hatchery were also provided to the San Leandro hatchery, thus making the origin and genetic history of hatchery-bred rainbow trout somewhat diverse and complex. Rainbow trout eggs and fry from these two hatcheries were the original source of most artificially propagated rainbow trout in the world.

Polyphyly of stonei
The potential polyphyly of stonei was recognized by Behnke (1979, pg. 134) from anatomical characteristics "...stonei would be useful only as name for the trout of a particular geographical region (upper Sacramento River Basin), not as a natural evolutionary unit. I believe the great variability I found is the result of mixing of more than one ancestral form of redband trout, and with a coastal rainbow trout influence in some populations." Analyses of genomic sequence data has demonstrated that redband trout of the upper McCloud River (above McCloud Falls) are a separate and distinct lineage of rainbow trout, while redband trout of the Pit River are of Great Basin origin. The type material of stonei is similar to redband trout of the Pit River and Goose Lake while McCloud River redband trout are clearly differentiated anatomically from the type material of stonei. The taxon O. m. calisulat Campbell and Conway 2023 was created to apply to the native redband trout of the upper McCloud River.