Optivus agastos, Gomon, 2004

Gomon, Martin F., 2004, Two New Species of Roughy (Trachichthyidae: Optivus) from Coastal Waters of Southern Australia, Records of the Australian Museum 56 (2), pp. 173-178 : 174-176

Optivus agastos n.sp.

Figs. 1, 2; Tables 1, 2

Trachichthys elongatus (non Günther, 1859). Günther, 1859: 10 (partim); Waite, 1898: pl. V.

Hoplostethus elongatus (non Günther, 1859). McCulloch, 1923: 14; 1929: 132 (partim); Marshall, 1964: 129 (partim); Allen et al., 1976: 387 (partim).

Optivus elongatus (non Günther, 1859). Whitley, 1964: 40; McKnight, 1972: 154 (partim); Shimizu, 1977: 192; Kotlyar, 1980: 217 (partim); Paulin, 1979: 70 (partim); Last et al., 1983: 275 (partim); Hutchins & Swainston, 1986: 38 (partim); Kotlyar, 1992: 38; Kuiter, 1993: 72; Kuiter, 1996: 58.

Optivus sp. 1 .—May & Maxwell, 1986: 220; Gomon, 1994: 406; Kotlyar, 1996: 180.

Optivus n.sp. — Paxton et al., 1989: 365; Johnson, 1999: 725.

Type material. HOLOTYPE: NMV A24972-001 (90.3) Cape Wellington, Wilsons Promontory, Victoria, 39°04.1'S 146°28.6'E, rotenone, 2 February 1982, Kuiter , R.H. & M. McDonald . PARATYPES: AMS I.30408-007 (97.2), northeast of Wooli , New South Wales, 29°52'S 153°25'E to 29°48'S 153°26'E, 64 m, 2 May 1990, trawl, FRV Kapala ; AMS I.31476-005 (2, 64.3–91.5), off Murwillumbah , New South Wales, 28°20'S 153° 40'E to 28°25'S 153°41'E, 54–58 m, 15 August 1978, prawn trawl, FRV Kapala ; CSIRO H.3509- 01 (76.6), east of Lakes Entrance , Victoria, 37°55.5'S 148°12.4'E to 37°55.1'S 148°15.1'E, 42 m, 30 July 1993, demersal trawl, FRV Southern Surveyor, SS 05/93/102 ; CSIRO H.3989-02 (82.0), northeast of Newcastle , New South Wales, 32°52'S 151°54'E, 29–33 m, 19 April 1995, demersal trawl, FRV Kapala, K 95-03-10 ; CSIRO T1922 (95.2) , White Rock , Tasmania, 42°25'S 148°09'E, 96 m, 22 April 1980 ; NMV A2582 (80.0) , Brown Head , west shore, Wilsons Promontory, Victoria, 39°02.7'S 146°28.3'E, 0–16 m, 10 February 1982, rotenone, Cochrane , T.G., Kuiter , R.H. & Larsen, M .; NMV A2737 (4, 66.6–81.0) , Horn Point , north shore, Wilsons Promontory, Victoria, 39°01.6'S 146°28.2'E, 8 February 1982, Kuiter , R.H. & M. McDonald; NMV A3207 (46.5) , Portsea , Port Phillip Bay, Victoria, 38°19'S 144°43'E, 10 m, 11 August 1982, quinaldine, Kuiter , R. H.; NMV A24972-002 (5, 56.4–92,5) same data as holotype ; QM I.29706 (83.7) southeast of Point Lookout , Stradbrook Island, Queensland, 27°31'S 153°40'E, 80 m, trawl, 21 March 1995, collected by R. Joyce ; QM I.32705 (76.1) northeast of Cape Moreton , Queensland, 26°57'S 153°32'E, 104 m, trawl, 12 March 2001, Queensland Fisheries Service ; WAM P.25739-007 (83.6), Moreton Bay , 11.3 km (7 mi) northwest of Cape Moreton, southeastern Queensland, 23 February 1975, collected by R.J. McKay ; WAM P.28843-001 (84.8), Port Hacking , New South Wales, 34°04'S 151°07'E, trawl, 14 November 1974, collected by CSIRO.

Non-type material. Lord Howe Island AMS IA.678 & 679 (2, 76.6–85.8); Sydney HarbourAMS IB.7384 (15, 34.7–49.4); Sydney Harbour AMS I.40840-034 (12, 53.1–77.0).

Diagnosis. Gill rakers 22–25, modally 23; lateral profile of nape and head nearly straight in lateral profile, distinctly angled downward in front of dorsal fin; snout tip rounded, usually projecting slightly in front of upper jaw; depth of head at vertical through upper end of gill opening 2.9–3.2 times in SL; snout length 1.6–2.7 times in eye diameter; inner row of teeth on premaxilla noticeably longer than others; caudal peduncle relatively short and deep, depth 0.9– 1.3 times in length; dorsal and anal fins relatively low, third segmented dorsal-fin ray 3.5–4.2 times in SL, first anal-fin ray 5.2–6.3 times in SL; body greenish brown on back, silvery below; fins almost uniformly pink, though slightly dusky tips to caudal-fin lobes persisting in recently preserved large specimens.

Description. Dorsal-fin rays IV, 11 (V, 10 in one of 22 paratypes); anal-fin rays III, 9 (III, 10 in 2); caudal-fin rays 7 (8 in 1) + 19 (18 in 1) + 6; pectoral-fin rays 12 (11 in 2 and 13 in 5 of 36 fins counted); vertebrae 12 + 14; lateralline scales 28 (26–27); scales above lateral line approximately 12 (11–13); scales below lateral line approximately 18 (16–18); predorsal scales approximately 32 (31–36); ventral scutes 11 (9–13); total gill rakers 23 (20–24, modally 23; Table 2). (See Table 1 for morphometric values).

Body of moderate depth; caudal peduncle short and deep, tapering slightly posteriorly; anus positioned well behind pelvic-fin bases, just in advance of anal-fin origin; no apparent luminescent tissue. Head and snout rounded; dorsal outline of nape and head nearly straight in lateral profile, distinctly angled downward in front of dorsal fin; snout short, usually projecting slightly in advance of mouth; posttemporal spine short and sharp. Posterior edge of preopercle finely serrate, posteroventral corner produced as broad spine reaching just beyond hind edge of operculum. Dorsoposterior corner at rear end of maxilla posterior to vertical through posterior margin of orbit. Gill rakers on upper limb of first arch long and slender.

Oral edge of premaxilla and dentary broadly covered with fine teeth, those in row on ventral-most edge of premaxilla only slightly, but noticeably longer than those on either side; dentigerous surface extending laterally around expanded anterior end of dentary to underside. Vomer naked; palatine covered with fine teeth.

Scales adherent, each with numerous rows of strong ctenii obscuring scale margins and making determination of squamation patterns difficult; single row of scales overlapping onto bases of dorsal and anal fins. Predorsal scales on dorsal midline of head reaching just in advance of vertical through centre of orbit on dorsal midline of head. Cheek scales reaching forward just in advance of vertical through posterior extent of orbit. Lateral-line pores mostly obscured by ctenii. Scales on ventral midline between pelvicfin bases and anus modified as moderately large bony scutes.

Dorsal fin short based, continuous, spines and rays increasing in length progressively to third soft ray, subsequent rays gradually decreasing in length; first soft ray unbranched, remaining rays branched; origin of fin above centre of pectoral fin. Anal fin short based, first spine tiny, spines and rays increasing in length progressively to second soft ray, subsequent rays subequal or decreasing slightly in length. Caudal fin distinctly forked. Posterior edge of pectoral fin curved, middle rays longest, first and last rays simple and short, second longer but also simple, others branched. Posterior tip of pelvic fin reaching about two thirds of way to anal-fin origin.

Preserved coloration (in alcohol). Pale to slightly dusky, body darkest dorsally; dorsal fin sometimes with dusky smudge dorsally; each caudal-fin lobe with dark longitudinal stripe.

Live coloration (see colour photo in Gomon, 1994, fig. 364). Deep violet brown dorsally, silvery violet below; fins translucent; medial fins whitish basally and distally, pink centrally; caudal fin with prominent longitudinal brown stripe on each lobe; dorsal fin with brown smudge distally; pectoral fin pink; pelvic fin pinkish white.

Etymology. agastos, Greek meaning “near kinsman” in reference to the similarity and presumed close relationship of this species to the type of the genus.

Distribution. Restricted to southeastern Australia between Noosa, Queensland in the north, Lord Howe Island to the east, Port Phillip Bay, Victoria to the west and Freycinet, Tasmania in the south, in the vicinity of reefs at depths of 1– 146 m.

Comments. Günther (1859) described Trachichthys elongatus on the basis of a “skin, in spirits” from Great Barrier Island, New Zealand, purchased from Sowerby and subsequently registered as BMNH 1850.12.3.1 and “young” from Australia, presumably BMNH 1854.11.1.7 (40.5). Registration details and the jar label accompanying the latter lack locality information, recording only “purchased of Mr Stevens” (A.C. Gill, pers. comm.). The measurements provided with Günther’s description are clearly of an adult specimen and approximate those of the New Zealand specimen (c. 82 mm SL). The figure cited at the beginning of Günther’s species account apparently was not published.

The New Zealand specimen is here designated lectotype. The presumed Australian specimen, despite having paralectotype status, is likely to represent the species described above .

Superficially, O. agastos closely resembles O. elongatus both morphologically and with respect to coloration. It differs from the latter in usually having fewer gill-rakers on the front of the first gill arch (22–24, rarely 25, versus 25–27, rarely 24; Table 2), slightly smaller eye and longer snout, and taller teeth along the inner margin of the jaws, rather than teeth that are little, if at all enlarged.

Values for the number of oblique scale rows for the three species presented by Kotlyar (1996) that distinguish between O. sp. 1 (= O. agastos ) and O. elongatus do not match those recorded for this study. Specimens of O. elongatus listed above have 59–71 rows (47–51 in Kotlyar), whereas those of O. agastos have 63–71 (62–71 in Kotlyar).

The discrepancy is likely attributable to the difficulty in identifying individual scale rows associated with scale structures and patterns, discussed above in Methods and Materials.

Gomon (1994) stated that O. elongatus occurs at Lord Howe Island, as well as in New Zealand. The two Australian Museum specimens on which the statement was based (listed above in Non-type material) have characters consistent with O. agastos , including a gillraker count of 24.