Splitnose Rockfish, Sebastes diplopora
Splitnose Rockfish, Sebastes diplopora. Fish caught from coastal waters off San Pedro, California, November 2022. Length: 20 cm (7.9 inches). Catch, photograph and identification courtesy of Zachary Fratello, Redondo Beach, California.
The Splitnose Rockfish, Sebastes diplopora, is a member of in the Rockfish and Scorpionfish or Scorpaenidae Family, that is also known as the Lobejaw Rockfish, the Rosefish and the Splitlip and in Mexico as rocote doble hocico. Diploproa means “double prowed” in reference to the tooth bearing knob in the front of the upper jaw that forms a deep notch between the jaws. Globally, there are one hundred eight species in the genus Sebastes, of which fifty-three are found in Mexican waters, all in the Pacific Ocean. The Splitnose Rockfish is scientifically interesting as the juveniles have been found to have phaeohypohomycosis caused by infection with fungi of the genus Deviesia, the first case of this type of fungus causing disease in animals.
The Splitnose Rockfish is deep fusiform body and a relatively small species that has many sharp head spines and large eyes. The upper jaw is split with a notched upper jaw with large knobs on either side. They are light pink, pale orange or white with darker pink, orange or red blotches or bars on the upper body, head and fins. The dorsal fin spines have white tips and the membranes between each spine are dark fringed. Their body is deep with a depth that is 34 to 38% of standard length. Their anal fin has 3 spines and 5 to 8 rays; their caudal fin is slightly lunate; their dorsal fin has 13 spines and 11 to 14 rays; and, their pectoral fins have 17 to 19 rays. They have 32 to 38 gill rakers and their body is covered with scales.
The Splitnose Rockfish is a demersal species that is found as solitary individuals or in small schools within lower relief rocky habitat and sloping reefs on the continental shelf at depths. The juveniles are pelagic and found among drifting kelp at the surface and eventually settle on the seabed over soft substrate. They are found at depths up to 800 m (2,600 feet). They reach a maximum of 46 cm (18 inches) in length and 810 grams (1 lb 12 oz) in weight. As of December 1, 2024, the International Game Fish Association world record stood at 2.90 kg (1 lb 12 oz) with the fish caught in coastal waters off San Clemente Island, California, March 2001. Juvenile Split-nose Rockfish consume planktonic animals but with the larvae feeding on zooplankton and the larger juveniles on amphipods and with maturity change their diet changes to amphipods, copepods, decapods, fishes, krill and shrimp. In turn they are preyed upon by Rock Sea Bass, Kelp Bass, and numerous kinds of Sea Lions. They are slow growing, long-lived that reach maturity at age 20. Reproduction is ovoviviparous with internal fertilization with fecundity ranges between 14,000 to 255,000 eggs and planktonic larvae and pelagic juveniles. They have lifespans of up to eighty-six years.
The Splitnose Rockfish is a resident of Mexican waters of the Pacific but has a very limited distribution being found from Isla Cedros, Baja California, northward along the central and northwest coasts of the Baja Peninsula.
The Splitnose Rockfish is very easily confused with the Aurora Rockfish, Sebastes aurora, and the Chameleon Rockfish, Sebastes phillipsi, but both lack the deep notch between the upper jaws and lack large eyes.
From a conservation perspective the Splitnose Rockfish has not been formally evaluated. They are a component of the West Coast commercial fishery caught by long-line and otter trawls. They are rarely caught by recreational anglers. Due to their slow growth and late maturity.