Anatomy and identification features

All Sebastes species possess a laterally compressed body and large spiny heads. The preorbital bone has one or two spinous points over the maxilla. The sub-orbital ridge has no spine and is generally weakly marked. All preopercular spines are about equal in length, a supplemental preopercular spine is absent. Other important spines for the identification of Sebastes are: the upper post-temporal spine, the supra-cleithral spine, two opercular spines, the nasal spine, the pre-, supra- and post-ocular spine and the parietal spine. The symphysis of the lower jaw is more or less developed as a rounded protuberance or sharply projected. There is no occipital pit. The dorsal fin is equipped with 14 to 16 strong spines and 12 to 17 rays, the anal fin with three spines and six or more rays, the pectoral fins have no spines and 17 to 21 rays, the pelvic fins have one spine and three to five rays. All scales are ctenoid and are found on all parts of the skin, including the head, cheek and snout. There are 30 to 40 (mostly 32 to 34) scales on the lateral line. The four Sebastes species of the Northeast Atlantic have a bright red colour, whereas the body of Sebastes species of the North Pacific can also include other colours like white, yellow and brown.

Morphological determination features of the Sebastes species of the Northeastern Atlantic are given in Whitehead et al. (1986). The determination of S. viviparus from the other three redfish species is possible by counting the number of oblique scale rows below the lateral line (less than 55 on S. viviparus and more than 55 on S. fasciatus) and determining the direction of the lower preopercular spine (backward or obliquely backward or downward on S. viviparus and downward or obliquely forward and downward on S. fasciatus). S. fasciatus is determined from S. marinus and S. mentella by the number of anal fin rays (seven on S. fasciatus, eight to ten on S. marinus and S. mentella), the number of parietal spines on each side of the head (two on S. fasciatus, one on S. marinus and S. mentella) and the number of vertebrae (30 in S. fasciatus, 31 to 32 in S. marinus and S. mentella). S. marinus and S. mentella can be distinguished from each other by a symphyseal knob (absent on S. marinus, well developed and sharply projected on S. mentella), the eye-diameter relative to the body length (S. mentella having the larger eye) and the number of pores on the front side of the supra-occipital commissure between the parietal ridges (four on S. marinus and two or three on S. mentella). Identification features for redfish are also discussed by Templeman and Sandeman (1957), Trout (1961), Alverson and Westrheim, 1961, Barsukov (1968), Barsukov and Zakharov (1972), Litvinenko (1974), Ni (1981, 1982 and 1984) and Kenchington (1986). The identification features of larvae and juveniles of are reviewed by Kendall (1991).

In the Irminger Sea and the Labrador Sea, S. marinus and S. mentella are hard to distinguish from each other and several intermediate forms are found. The use of biochemical analyses of haemoglobin and enzyme patterns show small differences between the species (Nævdal, 1978; Rehbein, 1983; Nedreaas and Nævdal, 1989 and 1991; Nedreaas et al., 1994), whereas in the Norwegian Sea and in Faroese waters, morphometric and meristic measurements are sufficient for the determination in most cases (Reinert and Lastein, 1992).

Sexual dimorphism:

Males and females of the Sebastes species in the North Atlantic show little sexual dimorphism, as do most species of the Scorpaenidae (Bond, 1996). The males of S. marinus can only be distinguished from the females by the presence of a genital papillus (Kotthaus, 1950; Muus and Dahlström, 1991). Females of S. mentella were found to grow faster than males of the same species (Magnússon and Magnússon, 1995; Rikhter, 1996). Several studies on sexual dimorphism in the Sebastes species in the North Pacific show a more distinct separation in several rockfish species (Lenarz and Wyllie Echeverria, 1991).

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