The splitnose rockfish (Sebastes diploproa) is distinguished by having a deeply notched upper jaw, which inspired its Greek name diploproa, meaning "double prow." The splitnose rockfish is also called banjo, splitlips, rosefish, channel cod, redfish, red rock cod, and lobe-jawed rockfish, among other names. In addition to being notched, the upper jaw has a prominent knob on either side. Splitnoses may have white on the tips of each dorsal fin spine and dark coloring on the membranes between the spines. Underwater the adults are pale pink or white with patches of darker pink, orange, or red on the dorsal areas. The back and sides change to dark pink or red after capture, while the pale belly coloration remains unchanged. Pelagic juveniles are golden with a large eye. Their head, body, and fins are covered with tiny brown speckles.

The range of the splitnoses spans between Prince William Sound, in the northern Gulf of Alaska, to central Baja California. Adults have been found at depths between 299 ft. and 2,622 ft. (91-795 m), although they are most commonly found at depths ranging from 705 ft. to 1,155 ft. (215-350 m) between British Columbia and southern California. Young juveniles begin living at the surface, move to midwater depths after several months, and eventually live at the bottom after nearly a year of life. During their first year, splitnoses have been found living among drifting vegetation in Puget Sound and southern California, and under floating objects in Queen Charlotte Sound, British Columbia. Using subtle body motions, adults often create sheltered shallow depressions in the soft substratum on the seafloor. While solitary individuals are usually found resting on the bottom, the schooling splitnoses occur well above the seafloor. Newly spawned splitnoses feed primarily on calanoid copepods and amphipods. Krill and sergistid shrimp are added to their diet as they grow. The splitnoses are prey to Steller sea lions and other pinnipeds.

About 14,000 to 255,000 eggs are produced by females, depending on size (more for larger sizes). This species has a long reproductive period. Females release larvae during all months, most commonly in summer and fall. In British Columbia there may be two periods of larval release. At the time of release, larvae are about 0.2 in. (4.4-5.2 cm), growing to about 0.8 in. (2 cm) as pelagic juveniles. Splitnoses have been aged to at least 86 years and reach a maximum size of 18.4 in. (46 cm). While the males grow to maximum lengths earlier than females, the females grow faster and larger than males. Age and size at maturity varies for both sexes depending on geographic location.

Splitnoses are significant to the Washington trawl fishery, where they are commonly taken incidentally with other rockfish. They are less important off British Columbia. In areas of high abundance off California, splitnoses are targeted for catch. Their market value is limited due to their small size and they are rarely caught recreationally.

Adapted from Yoklavich, M. 2002 Sebastes diploproa, p. 162-164. In M. S. Love, M. Yoklavich, and L. Thorsteinson, The rockfishes of the northeast Pacific. Univ. California Press.

AFSC Rockfish Guide