Lucigadus borealis Iwamoto and Okamoto, 2015

Iwamoto, Tomio & Okamoto, Makoto, 2015, A New Grenadier Fish of the Genus Lucigadus (Macrouridae, Gadiformes, Teleostei) from the Emperor Seamounts, Northwestern Pacific, Proceedings of the California Academy of Sciences 62 (13), pp. 369-380 : 372-377

Lucigadus borealis Iwamoto and Okamoto , new species

Figures. 2 a-b, Table 1

No literature refers to this species.

DIAGNOSIS.— A species of Lucigadus with 1D II,9–10; V 13–17; inner gill rakers on first arch 12–15; lateral-line scales over distance equal to predorsal length 35–42; pyloric caeca 11–17; length upper jaw 29–33% HL; length outer gill slit 13–17% HL. Body lacking dark bands or notable markings; anterior one-third or more of first dorsal fin blackish, with dark pigmentation sometimes more extensive distally; paired fins overall dark; anal fin almost entirely dark except near base of anterior rays, especially in smaller individuals; rays of second dorsal and anal fins black near posterior tip of tail.

TYPE-SPECIMENS.— Holotype: CAS 237107 (female, 165 mm TL, 24.8 mm HL); Emperor Seamounts, Koko Guyot; 35°39′N, 171°01′E; 409 m; 14 June 2011 . Paratypes (all collected with holotype) : CAS 237109 (5: 18.5–29.0 mm HL, 113–198 mm TL) ; NSMT 237108 (1: 25.0 mm SL, 162 mm TL) .

DESCRIPTION.— Counts and measurements of the type-specimens are provided in Table 1. General features of the fish are best seen in Figs. 2 a-b. Head relatively short, approximately 15% of TL, somewhat longer than greatest body depth (under origin of first dorsal fin); tail greatly compressed, long and straplike, ending in a slender, almost-filamentous tip. Orbit slightly oval with long axis diagonal, greatest diameter more than length of snout and about equal to or slightly more than postorbital length; upper rim of orbit not entering dorsal profile. Snout broadly rounded in lateral view, with steep ventral profile; scarcely protruding beyond upper jaw and without acute ridges or sharp angles; no stout tubercular scales at tip and lateral angle. Suborbital region relatively flat and vertical, lacking a sharp, stoutly scaled longitudinal ridge. Mouth small, upper jaw about one-third or less of HL, extending posterior to point below anterior edge of pupil; lips relatively thick and fleshy, but not extremely so. Gill membranes narrowly connected across isthmus at point below middle of orbit. Chin barbel small, slender, its length about equal to narrowest width of suborbital (except in one small specimen of 18.1 mm HL where it was 27% of HL; others between 13% and 18% HL).

Origin of pelvic fin under opercle, pectoral fin slightly posterior to that vertical, and first-dorsal fin well behind that. Origin of anal fin under middle third of first dorsal fin. Height of first-dorsal fin about equal to HL, base of fin relatively steep and short (length of base about one-third or less of HL); pectoral and pelvic fins less than three-quarters of HL, none of the rays notably prolonged.

Squamation typical of other members of genus, with small scales uniformly covering most of head. Gular membrane naked, but bases of ventral-most 1–3 branchiostegal rays have a few small scales. Body scales small, typically covered with 5–8 mostly parallel rows of short, erect, conical spinules with slightly recurved tips.

Teeth in both jaws small and in short wide bands, widest anteriorly; outer series of premaxillary teeth slightly enlarged.

Gill rakers short, tubercular, covered distally with minute spines. Gill arches connected by membrane at dorsal and ventral ends; the outermost and innermost gill slits greatly restricted.

Color in preservative overall light brown over dorsal aspects of head and trunk; bluish over abdomen and chest regions, with silvery reflections on ventral surfaces of trunk and head, and lateral face of pectoral-fin base. Dorsally, trunk darker than all of tail. Periproct and bases of pectoral and pelvic fins black; fin coloration otherwise as described in Diagnosis. Underside of head relatively pale, lips, chin barbel, and mouth lining pale; most inner surfaces of gill cavity immaculate, but outer margins and rims of first and fifth gill slits heavily punctate; gill filaments pale, but arches and gill rakers gray. Branchiostegal membranes rather heavily speckled, as are lateral and ventral surfaces of lower jaw, and to a lesser extent, the operculum. Heavy punctations on body seen in some other members of genus lacking in the new species.

ETYMOLOGY.— From the Latin borealis , northern, in reference to the northern distribution of the new species.

COMPARISONS.— Lucigadus borealis is most similar in overall appearance to L. nigromarginatus from the Philippines, Taiwan, and the East Indies, but the two species are readily differentiated by the latter having fewer pelvic-fin rays (10–11 vs. 13–17), fewer inner gill rakers on first arch (10–12 vs. 12–15), smaller orbit (30–36% HL vs. 36–45% HL), and longer upper jaw (33–39% HL vs. 29–33% HL). Lucigadus lucifer , L. acrolophus , and L. microlepis also have fewer pelvic-fin rays as well as other differentiating features (see Table 1); L. microlepis is unique in the genus in having a banding pattern on the body and on vertical fins. Lucigadus nigromaculatus and L. ori have high pelvic-fin ray counts like L. borealis , but neither of those two have such a short outer gill slit as L. borealis (13–17% HL vs. 18–31% HL), a short upper jaw (29–33% HL vs. 33–45% HL), and so few pyloric caeca (11–17 vs. 30–60). Unlike L. borealis with a dark anterior one-third or so of the first dorsal fin, L. nigromaculatus and L. ori have a prominent black blotch distally on the fin. (Note that we have treated L. potronus as a synonym of L. nigromaculatus .)

DISTRIBUTION.— The new species is known only from one collection in a bottom trawl in 409 m on the Koko Guyot located near the southern end of the Emperor Seamounts. The capture of Lucigadus borealis is from a latitude farther north than any previously recorded specimen of the genus Lucigadus . So far as we can ascertain, the most northern previous record of the genus is off Taiwan near the Tropic of Cancer at around 23°N ( Chiou et al. 2004:45, for a L. nigromarginatus specimen misidentified by those authors as Lucigadus lucifer ). There are no records of the genus from off Japan. Most other records of the genus are from tropical waters of the western Pacific or subtropical waters of the southern hemisphere including Australia, South Africa, and South America. With the exception of L. borealis , the genus is not known from the Pacific Plate.

DISCUSSION.— The fish fauna of the Emperor Seamounts is composed of many wide-ranging bathypelagic and thalassobathyal species of boreal waters in addition to a number of endemic species ( Novikov et al. 1981; Borets 1986). Based on his study of fishes collected by Soviet vessels on eight seamounts of the Emperor Seamounts (“Northwestern range”) and eight of the Leeward Isles (“Hawaiian range”), Borets (1986) recognized six “biotypes” based on water mass and bottom relief, with each biotype having its own “ichthyocene,” viz., its characteristic species composition. Up to that time (1986), Borets found 80 fish species recorded from the Emperor Seamounts and 55 species from the Leeward Isles, with 39 species common to both regions; he list- ed only six grenadier species.

Wilson and Kaufmann (1987) provided a comprehensive review of the world’s seamount biota and their biogeography. Of the 449 seamount fish species in 92 families that these authors found recorded in the literature and in unpublished sources, the grenadiers were best represented with 39 species. Subsequent to their work, many more fish species, including grenadiers, have been record- ed from an expanded list of seamounts whose fauna has been sampled (see for example, Sazonov and Iwamoto 1992; Iwamoto and Merrett 1997; Merrett and Iwamoto 2000). Nevertheless, their basic assumptions of seamount biogeography remain valid. The most diverse families represented had many, and some exclusively, deepwater members, and “their importance probably reflects the fact that over 60% of the seamounts were sampled at greater than 300 m depth” (Wilson and Kaufmann 1987:364). These authors distinguished four main biogeographic categories in the seamount biota: (1) provincial — confined to the general region of the seamount; (2) widespread to cosmopolitan; (3) exotic — rarely or never before found in the immediate region; and (4) endemic —confined to a particular seamount or several seamounts of a particular group. One or another of the Emperor Seamounts grenadiers appears to fall into each of these categories.

Grenadiers of the Emperor Seamounts are represented by at least 15 species, including the new Lucigadus here described and the Coelorinchus species recorded by Sazonov (1994:111) from one specimen that he thought may be a variant of his new species C. anisacanthus . Subsequent to Sazonov’s original description, the first author (TI) has examined five specimens of that “variant” at HUMZ; those specimens confirmed the morphological differences from C. anisacanthus that Sazonov found in his single specimen and are without much doubt an undescribed species. Two other species, a Kuronezumia and a Nezumia , both unidentifiable, were examined by TI in the collections of HUMZ in 2010.

Of the 15 grenadier species, four appear to be endemic: Coelorinchus anisacanthus , Coelorinchus sp. cf. anisacanthus , Lucigadus borealis , and Nezumia tinro . The unidentified Kuronezumia and Nezumia may also represent endemic species. Lucigadus borealis could also be categorized as an exotic species, in that it displays a highly disjunct distribution from its congeners, none of which are found in the immediate region.

Five species can be considered as provincial: Nezumia obliquata , known from off Kauai in the Hawaiian Islands and Ojin Guyot in the Emperor Seamounts; Coelorinchus matsubarai known from the Kyushu-Palau Ridge and the Emperor Seamounts (Kammu Guyot and Koko Guyot; and also Colahan Seamount in the Northwestern Hawaiian Islands, although that seamount is sometimes consider part of the Emperor Seamounts [see Wikipedia 2014]); Hymenocephalus hachijoensis from the Kyushu-Palau Ridge and the Emperor Seamounts (Kammu Guyot and Nintoku Guyot); and Coelorinchus gilberti , a species with a peculiar distribution for a Coelorinchus of the North Pacific Ocean, ranging from southern Japan (33°N) north to off Hokkaido and also off the Kyushu-Palau Ridge and the Emperor Seamounts (32°41.6′N, 172°18.8′E, Yuryaku Guyot; 5 specimens, HUMZ 132360 to 132364). Bathygadus antrodes is somewhat exceptional in ranging from off Okinawa to central Japan (Honshu) to the Emperor Seamounts (Nintoku Guyot).

The remaining species are in the widespread category (but not cosmopolitan) and appear to have broad distributions in boreal waters of the North Pacific. Wilson and Kaufmann (1987:369) describe a faunal component of the Emperor Seamounts whose species follow the Pacific rim from northern Japan to northern Baja California. They provide as examples two grenadiers, Albatrossia pectoralis and Coryphaenoides acrolepis , to which should be added C. cinereus and C. filifer . The first two species have a disjunct distribution having also been recorded from the southwestern Atlantic off the Falkland Islands (Brickle and Laptikovsky 2002; Laptikovsky et al. 2013). Albatrossia pectoralis has also been captured in the western Pacific well to the south of Japan at Iwo Retto or Volcano Is. (24°12′N, 149°58′E, about 750 n. mi. ne. of the Mariana Trench National Marine Sanctuary in 1200 m; HUMZ 71918). That species has a long pelagic larval stage (see Endo et al. 2010), and juveniles do not become benthopelagic until attaining about 51–55 cm TL (Orlov and Tokranov 2008). Coryphaenoides longifilis more or less follows a Pacific-rim distributional pattern except that it has not been recorded in the eastern North Pacific, aside from the Bering Sea.

What seems evident with the widespread species (and the exceptional Bathygadus antrodes and Coelorinchus gilberti ) is that they have followed the pathway provided by the Emperor Seamounts to extend their distributions along the continental margins southward and deep into the North Pacific basin. These species may use seamounts along a chain as stepping stones, a hypothesis suggested by Hubbs (1959) and further supported by Wilson and Kaufmann (1987) for seamount species exhibiting trans-oceanic dispersal. Some grenadiers appear to have long-lived pelagic larvae and juveniles, which with propitious currents could allow widespread dispersal to the limits of their physical and physiological tolerances. Arkhipkin et al. (2010) have postulated an antipodal link between the North Pacific and South Atlantic based on changes in deep-water circulation patterns. Albatrossia pectoralis and Coryphaenoides acrolepis are possible candidates in this category; Laptikovsky et al. (2013) have suggested that such changes in deep-water circulation patterns create a “deepwater conveyor” that could transport the fish through the South Pacific, around Cape Horn, and into the South Atlantic.

Figures

FIGURE 2a (above). Lucigadus borealis Iwamoto and Okamoto, sp. nov.. Holotype CAS 237107, lateral view. Koko Guyot, Emperor Seamounts. FIGURE 2b (below). Lucigadus borealis Iwamoto and Okamoto, sp. nov.. Holotype CAS 237107, dorsal view. Koko Guyot, Emperor Seamounts. Scale bar = 1 cm.