Blue rockfish have a relatively smooth and oval appearance compared to other members of Sebastes, with very few head spines. Color is a bluish black to gray, with some darker mottling, including a pair of stripes angling down and back from the eye. The terminal mouths are small for rockfish. Length ranges up to 55 to 60 cm, and weights up to 3.8 kg.
They occur from Sitka Strait in the north to Punta Santo Tomas in Baja, most commonly along Oregon and northern California (records of blue rockfish in the western Gulf of Alaska and the Bering Sea probably refer to the related dusky rockfish.) While they have been caught at depths of over 500 m, most live near to the surface, down to 90 m.
Diet is plankton. Juveniles consume tiny crustacea such as copepods and barnacle larvae (in some cases having a significant effect on the population), while adults shift to larger types, such as free-swimming tunicates, jellyfish, gastropods, squids, young rockfish, and drifting plant fragments.
Blue rockfish were once an important part of the California fishery; they were the most common rockfish marketed in San Francisco and San Diego during the 19th century, but have since declined in popularity. They continue to be of interest as game fish, and are among the most common types landed by boat anglers; in fact, there is evidence of overfishing in Monterey Bay and southern California.
The species epithet mystinus derives from the Greek for "priest", referring to the overall dark color.