Hoplostethus melanopeza, Roberts & Gomon, 2012

Roberts, Clive D. & Gomon, Martin F., 2012, A review of giant roughies of the genus Hoplostethus (Beryciformes, Trachichthyidae), with descriptions of two new Australasian species., Memoirs of Museum Victoria 69, pp. 341-354 : 346-351

Hoplostethus melanopeza sp. nov.

New Zealand giant sawbelly

Figures 2–5 ; Tables 1 & 2

Hoplostethus gigas (not McCulloch, 1914). Paulin & Stewart, 1985: 31, listed, Bay of Plenty, 100–300 m, first record for New Zealand. – Paulin et al., 1989: 153, 257, colour plate (opposite page 163), key. –Gomon, in Gomon et al., 1994 (in part): 403, Fig. 361, description, off Sydney, NSW, and Bay of Plenty, New Zealand.

Hoplostethus? gigas (not McCulloch, 1914). Roberts, 1995: 106, colour figs, description, Bay of Plenty. – Roberts, 1996: 40, colour fig., description, Bay of Plenty.

Hoplostethus cf. gigas (not McCulloch, 1914). Roberts et al., 2009: 532 (listed). – Roberts, 2012: 38 , colour fig., description, off Mayor Island, Bay of Plenty.

Material examined. Holotype. NMNZ P.053205 (286) New Zealand, North Island, Bay of Plenty, Mayor Knolls, 12 km east of Mayor Island , 37°19.07' S, 176°25.35' E, 320 m, gill net, 3 hr soak, 5 March 2012, FV Ruben Jack, A. Oliver & C. Molloy.

Paratypes. (27, 72.6–515 mm SL). AMS I.27085–001 (515) Australia, New South Wales, Taupo Seamount , 32° S, 155° E, March 1982 ; AMS I.30415–001 (2, 72.6–123) Australia, New South Wales, Moruya , 36°03' S, 150°27' E, 383 m, 21 November 1979, K. Graham ; AMS I.40390–004 (108) Australia, New South Wales, Bermagui , 36°47' S, 150°21' E, 585 m, 23 July 2000, K. Graham ; CSIRO H5321–04 (107), Australia, Victoria, Cape Everard , 38°14' S, 149°36' E, 486–602 m, 23 July 2000, K. Graham ; CSIRO H7387–01 (380) formerly NMNZ P.053725, New Zealand, Bay of Plenty, east of Mayor Island, west of Rangitira Knoll , 37°15.52' S, 176°44.41' E, 500 m, set net, April 2012, FV Ruben Jack, OPC Fish & Lobster Ltd, A Oliver & C Molloy ; MNHN 2012–0268 (273) formerly NMNZ P.053206, same data as holotype ; NMNZ P.014162 (465) New Zealand, North Island, Bay of Plenty, Rangitira Knoll , 37°15.5' S, 176°51' E, 140 m, June 1983, G. Schroeder ; NMNZ P.015181 (2, 440–450) New Zealand, Tokokemoke Knoll, 12 miles west of White Island , 37°28' S, 176°54' E, 256 m, longline, FV Arapawa I, C. Walker ; NMNZ P.015854 (3, 397–467) New Zealand, North Island, Bay of Plenty, Rangitira Knoll , 37°15' S, 176°51' E, 366 m, February 1984, gill net, G. Schroeder ; NMNZ P.031100 (3, 449–482) New Zealand, North Island, Bay of Plenty, southeast of Rangitira Knoll , 37°17.2' S, 176°53.6' E, 240–500 m, April 1994, bottom trawl, FV Margaret Philippa, J. & J. McGrath ; NMNZ P.038312 (99) New Zealand, southern Kermadec Ridge, outer Bay of Plenty, Rumble 3 submarine volcano, 35°44.51' S, 178°29.62' E, 270–426 m, epibenthic sled, 11:31–11:51 hrs, 19 May 2001, GRV Tangaroa ; stn.TAN 0107/004 ; NMNZ P.038325 (395) Gascoyne Seamount , 36°42.00' S, 155°54.00' E, 925 m, 8 August 2001, dropline, D. Smith ; NMNZ P.038548 (178) same data as NMNZ P.015854 ; NMNZ P.047799 (132) Tasman Sea, Lord Howe Rise, Central Plateau 34°11.95' S, 162°38.90' E, 712–760 m, 7 September 2010, trawl, FV Voyager, OBS 3177/058, J. Houston ; NMNZ P.053308 (486) New Zealand, North Island, Bay of Plenty, east of Mayor Island , 37°19.75'S, 176°29.57'E, 540 m, set net, March 2012, OPC Fish & Lobster Ltd., coll. A Oliver & C Molloy ; NMNZ P.053877 (468) New Zealand, Bay of Plenty, Mayor Knolls, east of Mayor Island , 37°18.6' S, 176°31.32' E, 347 m, set net, April 2012, FV Ruben Jack, A. Oliver & C. Molloy ; NMV A22070 (128) Tasman Sea, Lord Howe Rise , 33º38' S to 33º40'S, 162º21'E to 162º28'E, demersal trawl, 300–750 m, 22 March–2 April 2001, coll. K. Smith ; NMV A30942-001 (282) formerly NMNZ P.053307, New Zealand, Bay of Plenty, east of Mayor Island , 37º19.75' S, 176º29.57' E, set net, 540 m, March 2012, FV Ruben Jack, OPC Fish & Lobster Ltd., coll. A. Oliver & C. Molloy ; NMV A30943–001 (393) formerly NMNZ P.053726, New Zealand, Bay of Plenty, E of Mayor Island, Rangitira Knoll , 37º15.522'S, 176º44.408'E, set net, 500 m, April 2012, FV Ruben Jack, OPC Fish & Lobster Ltd., coll. A. Oliver & C. Molloy ; NMV A30944–001 (420) formerly NMNZ P.054048, New Zealand, Bay of Plenty, E of Mayor Island, Maungaiti Knoll , 37º17.25' S, 176º51.63' E, set net, 450 m, June 2012, FV Ruben Jack, OPC Fish & Lobster Ltd., coll. A. Oliver ; USNM 406863 (262) formerly NMNZ P.053529, New Zealand, North Island, Bay of Plenty, Mayor Knolls, 12 km east of Mayor Island , 37°19.07' S, 176°25.35' E, 320 m, 5 March 2012, FV Ruben Jack, coll. A. Oliver & C. Molloy.

Diagnosis. Pectoral–fin rays 15, rarely 13, 14 or 16; total gill rakers on outer side of first arch 18–21; abdominal scutes 9–12, some scutes in large individuals with multiple apical points; predorsal scales, 16–22; isthmus lacking scales; body scales adherent; lateral–line scales with strong medial ridge, but no spine in small and medium sized adults, with strong spine centrally on posterior margin in large adults; scales on predorsal midline forming low raised ridge; body ovoid and deep, depth 1.9–2.1 in SL; nape gently curved, forehead almost straight to above upper lip; dorsal– and anal–fin spines of moderate thickness; body of adults grey, superimposed with deep red in life, outer margin of all fins with narrow black edge in adults; buccal cavity and opercular recess black, vomer, margins of mouth roof lateral to palatines, underside of tongue and upper surface of lower jaw stark white. Reaches at least 515 mm SL.

Description. (See Table 1 for frequencies of values for selected meristic characters.) Dorsal–fin rays VI, 13 ( VI, 12 in 2 and VII, 12 in 1 of 27); anal–fin rays III, 9 ( III, 10 in 1 of 27); caudal–fin rays 6 + 2 + 9 + 8 + 2 + 6 (7 + 2 + 9 + 8 + 2 + 6 in 2 of 21); pectoral–fin rays 15 (13 in 1, 14 in 2 and 16 in 4 of 54); pelvic–fin rays I, 6; gill rakers 6 + 1 + 13 (5 or 6 + 1 + 12–14 = 18–21, usually 6 + 1 + 13 = 20, mean total 19.7); lateral–line scales 27 + 1 (26–29 + 1, rarely 2, mean 27.7 + 1.1); transverse scales 12/1/25 (9–15/1/20–28; mean 11.1/1/23.4); predorsal scales 18 (16–22, mean 18.5); scutes 10 (9–12; Table 2); vertebrae 11 + 15; pseudobranch 19 (16–21); branchiostegal rays 8.

(See Table 1 for comparative ranges of selected morphometric characters.) Body ovoid and deep, depth 1.92– 2.08 in SL. Head large, its height slightly greater than its length, 94.1–114% HL; upper profile in front of dorsal fin gently curved to above rear of eye, then mostly straight to upper jaw, slightly concave above rear half of eye in some; anterodorsal profile only slightly separated from upper orbital rim; space between eyes wide, interorbital width 28.8–35.2% HL; eye of moderate size, orbital diameter 24.0–32.8% HL; crests of head bones strong, fine spinules on apices at skin surface; depressions between crests moderately deep, hidden by thick skin in adults; infraorbital bones becoming progressively broader with growth; nostrils immediately preceding orbits, posterior nostril two to four times area of anterior nostril; mouth reaching just beyond vertical through hind margin of eye; large, fine denticulate teeth covering oral margins and exposed lateral surfaces of premaxilla and dentary, palatine with narrow band of similar teeth, vomer apparently lacking teeth (with about 3 tiny teeth in small specimens); tip of dentary with ossified knob at symphysis. Preopercular spine short, reaching about 1/4 to 1/2 way from preopercular margin to pelvic–fin base, broad basally in large specimens. Humeral and preopercular spines of similar size. Longest gill raker about 2/3 eye diameter; gill filaments at angle of first gill arch very short, about 1/8 eye diameter and about 1/3 length of longest filaments of pseudobranch.

Body covered with adherent scales, scales densely covered with low, knob–like spinules above lateral line, posteriorly and low on side, scales above and covered laterally by pectoral fin, cycloid (cycloid scales distributed more ventrally in small individuals); head naked except for patch of scales on cheek posterior to rear tip of maxilla in about four vertical rows, posteriormost row with 8–12 scales; isthmus scaleless; lateral line with fine spinulation at free margin, each lateral–line scale with strong ridge but lacking distinct spine (no spine in small and medium sized adults, with strong spine centrally on posterior margin in large adults), considerably larger than other body scales, although adjacent scales intermediate in size between lateral–line scales and others away from lateral line; deep serrated abdominal keel formed from greatly enlarged scales (scutes) with spine–like apices, most without sculpturing or multiple tips, though with striations in some especially posteriorly; scales on dorsal midline in front of dorsal fin slightly but noticeably raised, their spinules not greatly enlarged. First dorsal–fin spine short, subsequent spines distinctly longer but only increasing slightly progressively in length; spines of moderate thickness, those posteriorly progressively wider with distinct lengthwise striations; first soft ray longer than last spine, subsequent rays progressively decreasing in length, outer margin of soft dorsal fin slightly curved. First anal–fin spine short, second only slightly or considerably longer, third long; spines of similar robustness to those of dorsal fin. Caudal fin distinctly forked, lobes of moderate breadth and rounded. Pectoral fin of moderate length, reaching to or beyond last few scutes (relatively longer in small individuals, to base of the third anal–fin ray in 99.3 mm SL paratype). Pelvic fin reaching just beyond middle scutes (to anal–fin origin in smallest paratype).

A large species, largest specimen examined 515 mm SL.

Colour in life. Head and body dark grey, obscured by deep red; opercle black suffused with red; dark areas of buccal and branchial cavities black; fins deep red with narrow black distal edges (figs 3 & 4).

Pigmentation in alcohol. Freshly preserved individuals dark grey (juveniles pale below a line between humeral spine and dorsal side of caudal peduncle near termination of dorsal fin base, dusky above); opercle dark; buccal and branchial chambers dark, including gill arches and rakers; vomer, roof of mouth lateral to palatines, underside of tongue and lower jaw uniformly pale; fins pale with narrow dark margins (juveniles with pale fins, except for slightly dusky outer portion of membrane between dorsal–fin spines).

Etymology. The name melanopeza is from the Greek melano for ‘black’ and peza ‘edge’, in reference to the characteristic black edge on all fins in large individuals of this species. As a noun in apposition, the spelling of melanopeza is not influenced by masculine gender of genus Hoplostethus .

Distribution. Confined to sub–tropical and temperate latitudes of the Tasman and South Fiji Basins in the south–western Pacific, documented from localities between about 33° and 37° S from south–eastern Australian slopes on the west to the outer Bay of Plenty and southern Kermadec Ridge at the north end of the North Island in New Zealand in the east (fig. 2). Occurs on continental slopes, seamounts and submarine rises with collection depths recorded between about 140 and 760 m, but most often 250– 400 m.

Comments. Hosplostethus melanopeza is very similar to H. gigas , a species with which it was confused in the early 1980’s when initial specimens were collected. The absence of detailed descriptive information beyond McCulloch’s initial description of H. gigas nearly 100 years ago no doubt contributed to this confusion. McCulloch evidently received the specimens on which his description is based well after they were preserved, saying about the species’ original colouration only that “when first received all the fins had traces of deep rose pink.” Although both species have a similar overall red or reddish–orange colouration, H. melanopeza has distinct black margins to all fins in large individuals, while the edges of only the medial fins appear to be no more than dark grey to blackish in large individuals of H. gigas . The recognition of the two species is supported by Cytochrome Oxidase subunit one sequences (Te Papa/ NIWA / CSIRO / NMV unpublished data).

Morphologically H. gigas and H. melanopeza have nearly identical ranges for meristic values, but the latter has a greater number of predorsal scales (16–22 versus. 9–15) and a higher mean value for total gill rakers of 19.7 versus 18.0, based on material examined. Proportional measurements for the two are also extremely similar. The greater size range of specimens for the new species makes a full comparison of the two impossible, although an examination of the distribution of values in a number of other species shows morphometric ranges converging at smaller sizes and the greatest disparities evident as individuals approach their maximum size. At comparable sizes H. melanopeza seems to have a slightly deeper body and shorter pelvic to anal–fin length than H. gigas (fig. 5).

Morphological comparisons with other nominal species referred to the subgenus H. ( Hoplostethus ) are difficult because of the relatively small sample sizes that literature descriptions on which most are based and the considerably greater variation detected when greater numbers are examined. In comparison with H. robustispinus , which reaches a comparably large size, H. melanopeza has 15, rarely 16, versus 17, rarely 16 pectoral– fin rays, 9–12 versus 11–13 abdominal scutes, 26 versus 27 total vertebrae, and medial fin spines of a moderate breadth versus broad in large individuals. The Indian Ocean H. confinis , as mentioned in the Introduction, also reaches a reasonably large size and has meristic values that are more similar to those of H. melanopeza and H. gigas , apparently differing from the former in having the same lower mean value of total gill rakers as the latter. It is further separable from H. melanopeza in lacking the black margins to its fins at a large size. Two other species occurring in the Indo–Pacific region have pectoral–fin ray numbers that appear to be comparable with H. melanopeza , the Red Sea H. marisrubri Kotlyar, 1986 and western Indian Ocean H. mikhailini Kotlyar, 1986 . Neither has been reported to have dark margins to their fins, but individuals of H. melanopeza do not appear to develop dark margins until they reach a standard length well in excess of 150 mm SL, a size that is greater than the largest specimen reported for either of these two species. Hoplostethus melanopeza differs from H. marisrubri in having 26 versus 27 total vertebrae and from H. mikhailini in having 18–21 versus 23–27 total gill rakers.

Although H. melanopeza , together with most other species of the genus reaching a significant size (apart from the commercially important orange roughy Hoplostethus atlanticus Collett, 1889 ), have long been regarded as very rare in deepwater environments. The type series took over 30 years to collect despite periodic requests to networks and the commercial and recreational fishing sectors (e.g. Roberts, 1995, 1996, 2012). The use of fishing gear such as deep droplines and set nets that are effective in capturing species living in rough bottom environments, have shown them to occur locally in greater numbers than originally thought. Even though life history details are yet to be identified for this and other giant roughy species, it is reasonable to believe their age and growth rate approach species like the orange roughy for which information is reasonably well known. Consequently, we urge restraint in the development of targeted commercial exploitation of what is potentially another long–lived, late maturing species, for which we currently have inadequate information on its abundance and biology.

Figures

Figure 2. Collection localities for specimens examined of Hoplostethus gigas (squares), H. melanopeza sp. nov. (circles) and H. grandperrini sp. nov. (diamonds). Red symbols indicate holotypes or lectotype.

Figure 3. Hoplostethus melanopeza sp. nov. A, NMNZ P.053205, holotype, 286 mm SL, photo by C. Struthers; B, NMNZ P.053308, paratype, 486 mm SL, photo by C. Struthers; C, NMV A22070, paratype, 128 mm SL, photo by M. Gomon.

Figure 4. Buccal colouration of Hoplostethus melanopeza sp. nov. NMNZ P.053206, paratype, 273 mm SL, photo by C. Struthers.

Figure 5. Selected proportional measurements relative to standard length for Hoplostethus gigas, H. melanopeza sp. nov. and H. grandperrini sp. nov.