Sebastes sp.

M. E. Anderson, D. L. Stein & H. W. Detrich, 2005, Additions to the ichthyofauna of the Tristan da Cunha Group, South Atlantic Ocean., Zootaxa 1072, pp. 27-33 : 30-32

Sebastes sp.

(Fig. 2)

A single juvenile rockfish was obtained from lobstermen by Mr. James Glass at Edinburgh and donated to us for description. It differs remarkably from the only known species at Tristan, Sebastes capensis (Gmelin) , by its rusty red colour without a trace of white blotches on the dorsum typical of the large subgenus Sebastomus Gill , and its lack of supraocular spines.

Rocha-Olivares et al. (1999) clarified the systematics of southern hemisphere Sebastes using mitochondrial DNA sequence variation. They concluded that S. capensis was widespread across the South Atlantic with an unsampled clade in the southeastern Pacific where it overlaps the range of S. oculatus . Both these species are clearly members of subgenus Sebastomus . Almost all juvenile specimens of S. capensis from Tristan known to date have been more orangish than our specimen, with the white blotches and with supraocular spines.

Mr John Hyde, Scripps Institution of Oceanography, La Jolla, California, has sequenced tissue samples of this specimen for the cytochrome b gene. He reports that out of the 1141 base pairs for the gene, 1138 match with 10 S. capensis from South Africa which he puts well within normal intraspecific variation in Sebastes and less than the difference between S. capensis and S. oculatus . Three unique nucleotide differences were found in the red specimen, suggesting along with the morphological differences, that it may represent an undescribed, cryptic species. However, Mr. Hyde reports that three nucleotide differences from one fish, with the small sample size of S. capensis , make it difficult to consider that our specimen represents a distinct species. Also, the nucleotide differences would not cause a change in the protein encoded by the gene. More specimens for confirmation are sought.

Dr. Paul Tyler, Darwin Project, U. K., sent the first author several underwater photographs of Sebastes capensis and Helicolenus mouchezi from Tristan taken during dives in late 2004 at depths of 15-25 m. One (Fig. 3) is of a red individual with poorly developed dorsal blotches and with small spots reminiscent of the northeastern Pacific S. constellatus Jordan and Gilbert . Thus, it appears that S. capensis at Tristan may exist as several morphotypes, possibly including the odd specimen in Fig. 2.

Counts: Vertebrae 8 + 17 = 25; D XIII, 14; A III, 6; P 18; C (branched rays) 12; gill rakers 8 + 1 + 17 + 3 pads; lateral line pores 38; pyloric caeca 9; vertical scale rows above lateral line 66; scales between lateral line and D origin 12. Head spines present: nasal, preocular, postocular, tympanic, parietal, supracleithral and cleithral. Head spines absent: supraocular, coronal and nuchal. Proportions in percent SL: head length 37.7; snout length 5.9; orbit diameter 11.7; interorbital width 5.1; lacrimal width 4.6; body depth 33.0; predorsal length 29.2; preanal length 69.0; prepelvic length 38.5; caudal peduncle depth 9.1; pectoral fin length 25.2; pelvic fin length 20.4; length 4th D spine 14.7; length 2nd A spine 18.8; spinous D base 35.2; rayed D base 22.7; A base 13.8. Both jaws and branchiostegal membranes naked. Interorbital concave. Symphyseal knob weak, ventral margin evenly rounded. No dentigerous premaxillary knobs. Body colour uniformly dark rusty red without white blotches, ventral part of abdomen whitish; fin membranes reddishorange except pectoral fin which is more red; irregular, black humeral spot present.

Material: SAIAB 74965 (male, 147 mm SL); Tristan da Cunha off Edinburgh; lobster trap; 50-70 m; 3- 6 July 2004; J. Glass.