Bothrocara nyx, Stevenson, Duane E. & Anderson, M. Eric, 2005

Stevenson, Duane E. & Anderson, M. Eric, 2005, Bothrocara nyx: a new species of eelpout (Perciformes: Zoarcidae) from the Bering Sea., Zootaxa 1094, pp. 53-64 : 54-61

Bothrocara nyx n. sp.

Figs. 1-4, Table 1

Holotype: UW 111798 , male, 158 mm, 58.512°N, 175.063°W, 1085 m , 28 June 2004, F/V Northwest Explorer, D. Stevenson .

Paratypes: (97 specimens) CAS 221001 , male, 100 mm, 54.382°N, 166.617°W, 798 m , 13 June 2004 ; CAS 221002 , 8 (4 males, 3 females, 1 unknown, 107-147 mm), 54.812°N, 167.678°W, 1064 m , 14 June 2004 ; LACM 56263-1 , 3 (118-167 mm), 54.284°N, 167.119°W, 1400 m , 19 July 2000 ; LACM 56264-1 , (NMFS 134,2004-01,36 LACM) 2 (males, 127n140 mm), 54.737°N, 167.601°W, 940 m , 15 June 2004 ; LACM 56265-1 , (NMFS 134,2004-01,90 LACM) 2 (1 male, 1 female, 150-163 mm), 58.237°N, 175.634°W, 858 m , 30 June 2004 ; SAIAB 75278 , male, 162 mm, 56.515°N, 172.259°W, 937 m , 24 June 2004 ; SAIAB 75279 , 5 (4 males, 1 female, 150-217 mm), 54.263°N, 166.7°W, 1105 m , 11 June 2004 ; USNM 380736 , 12 (9 males, 2 females, 1 unknown, 115- 183 mm), 54.271°N, 166.635°W, 1091 m , 11 June 2004 ; USNM 380737 , male, 157 mm, 58.509°N, 174.84°W, 1024 m , 28 June 2004 ; UW 46028 , female, 135 mm, 58.155°N, 175.607°W, 1016 m , 9 July 2000 ; UW 47449 , male, 92 mm, 59.588°N, 178.512°W, 924 m , 13 July 2000 ; UW 47557 , female, 129 mm, 59.59°N, 178.51°W, 916 m , 15 July 2000 ; UW 47834 , female, 168 mm, 54.209°N, 167.927°W, 1508 m , 12 June 2002 ; UW 111799 , 20 (9 males, 10 females, 1 unknown, 67-157 mm), 55.589°N, 168.871°W, 1016 m , 5 June 2002 ; UW 111800 , 3 (sex unknown, 122-125 mm) (C&S), 55.589°N, 168.871°W, 1016 m , 5 June 2002 ; UW 111801 , male, 208 mm, 54.209°N, 167.927°W, 1508 m , 12 June 2002 ; UW 111802 , female, 105 mm, 56.127°N, 169.118°W, 1161 m , 18 June 2004 ; UW 111803 , 21 (11 males, 10 females, 105-205 mm), 56.017°N, 168.880°W, 1177 m , 20 June 2004 ; UW 111804 , 7 (3 males, 3 females, 1 unknown, 158-195 mm), 56.017°N, 168.880°W, 1177 m , 20 June 2004 ; UW 111805 , 5 (2 males, 3 females, 125-152 mm), collected with holotype .

Diagnosis: A species of Bothrocara as defined by Anderson (1994), with vertebrae 17-19 + 90-98 = 108-116; pectoral-fin rays 12-15; vomerine teeth 0-3; gill rakers moderately long, 23-27; snout short, less than eye diameter; median occipital pore present; lateral line not visible on body; interior of mouth darkly pigmented.

Description: Vertebrae 18 (17-19) + 94 (90-98) = 112 (108-116); dorsal-fin rays 109 (103-112); anal-fin rays 93 (89-99); caudal-fin rays 10; pectoral-fin rays 13 (12-15); vomerine teeth 2 (0-3); palatine teeth 10 (0-10); gill rakers 6 (5-7) + 21 (17-21) = 27 (23- 27); pseudobranchial filaments 9 (7-10). Following measurements in percent SL: head length 19.4 (17.6-20.3); head width 7.8 (5.6-8.3); head depth 8.1 (8.8-11.4); pectoral-fin length 12.5 (9.9-14.4); predorsal length 17.9 (17.0-21.4); preanal length 33.9 (32.5-38.0); body height 8.5 (8.8-10.8); gill-slit length 9.1 (9.1-12.6). Following measurements in percent head length (HL): head width 40.1 (27.7-43.2); head depth 41.7 (43.4-59.6); upper jaw length 40.1 (36.4-43.5); pectoral-fin length 64.5 (49.8-72.4); pectoral base 9.1 (8.0-14.7); snout length 23.1 (17.8-26.0); eye diameter 27.0 (24.2-34.7); gill-slit length 46.9 (49.7-64.6); interorbital width 9.8 (8.4-16.4); interpupillary width 26.7 (22.0-34.6); caudal-fin length 22.1 (13.7-25.4). Pectoral-fin base/length ratio: 0.14 (0.14-0.22).

Body relatively long and compressed. Skin thin and delicate, particularly on head. Head ovoid in lateral view, with slightly convex dorsal profile and rounded snout; narrow in dorsal view, with widest point immediately posterior to orbit. Eye nearly circular, entering dorsal profile of head. Nostril tube short, not reaching upper jaw. Mouth subterminal, upper jaw extending approximately to mid-orbit. Lips thin. Jaw teeth conical, sharp, slightly recurved; premaxilla with two rows of teeth anteriorly diminishing to single row posteriorly, outer row largest; dentary with four rows of teeth anteriorly diminishing to single row posteriorly. Vomer with 0-3 small conical teeth arranged in transverse row. Palatine with 0-10 small conical teeth in single row, often protruding only slightly through skin. Suborbital bones seven. Gill slit extending anteroventrally to vertical through posterior margin of preopercle. Gill rakers relatively long, slender, pointed, slightly curved medially, with scattered dark chromatophores (Fig. 3A). Pseudobranchial filaments unpigmented, approximately as long as gill rakers.

Cephalic lateralis system with two pairs of nasal pores, one pair anteromedial to nostril tubes, the other pair posteromedial. Interorbital pore single, near vertical through anterior margin of pupil. Postorbital pores four. Single occipital pore present on midline. Suborbital pores eight or nine, six along ventral ramus of canal and two or three along ascending ramus of canal. Preoperculomandibular pores eight, four along dentary, one on anguloarticular and three on preopercle. Lateral line not visible on body.

Fins delicate, easily damaged. Dorsal-fin origin dorsal to pectoral-fin base, the first pterygiophore usually inserted in the second interneural space (rarely third or fourth), last dorsal-fin ray associated with third preural centrum. Anal-fin origin anterior to midbody, 0-2 anal-fin pterygiophores preceding first haemal spine, last anal-fin ray associated with third preural centrum. Caudal-fin rays ten, two borne on single epural, four on upper hypural plate, four on lower hypural plate. Pectoral fin long, with narrow base, extending to or nearly to anus.

Scales absent from head, cheeks, nape, pectoral fins, and abdomen; present on bases of dorsal and anal fins. Pyloric caeca two, short and stubby.

Color: In life, top of head and snout pale grayish-brown; cheek and opercle pearlescent white; lips, interior of mouth, and branchial chamber dark brown. Body pale grayish-brown, becoming dark brown to black at base of dorsal and anal fins, abdomen and prepectoral region pearlescent bluish white. Median fins dusky, with narrow dark margins. Pectoral fins nearly transparent. Peritoneum jet black; stomach heavily pigmented. In alcohol, head light brown with black lips and opercle; body light brown with distinct dark brown line along base of dorsal fin, black peritoneum visible through abdominal wall; dorsal and anal fins dusky with dark margin; pectoral fins nearly transparent, with some pigment along dorsal margin.

Distribution: This species is known only from the upper continental slope of the eastern Bering Sea, where it has been captured at depths ranging from 790 to 1508 m (Fig. 4).

Etymology: Nyx (Nux) is the Greek goddess of night and darkness. The specific epithet nyx, to be treated as a noun in apposition, alludes to the dark conditions prevalent in the deep waters and northern latitudes inhabited by this species, as well as the heavily pigmented lining of the mouth and visceral cavity.

Remarks: Anderson (1994) recognized seven species of Bothrocara : B. alalongum (Garman) , B. brunneum (Bean) , B. elongatum (Garman) , B. hollandi (Jordan and Hubbs) , B. molle Bean , B. pusillum (Bean) , and B. tanakae (Jordan and Hubbs) . Among its congeners, B. nyx is most commonly collected with B. brunneum on the Bering Sea slope. Although B. brunneum attains a much larger maximum size than B. nyx , the two species can be difficult to differentiate at small sizes (<150 mm SL). However, Bothrocara brunneum has more pectoral-fin rays (15-18 vs. 12-15) and pseudobranchial filaments (9- 16 vs. 7-10), as well as fewer gill rakers (18-22 vs. 23-27) than B. nyx . Bothrocara brunneum also has a higher pectoral-fin ratio (0.19-0.41 vs. 0.14-0.22) and longer snout (longer than orbit vs. shorter than orbit) than B. nyx , and lacks the dark pigment present inside the mouth of B. nyx .

Bothrocara pusillum is also common in the Bering Sea, although it is found in considerably shallower water than B. nyx (~200-500 m vs.>800 m). Bothrocara pusillum is similar to B. nyx in having a short snout and small maximum size (approximately 200 mm SL). However, B. pusillum has fewer and shorter gill rakers (12-15 vs. 23-27, Fig. 3), fewer pseudobranchial filaments (4-7 vs. 7-10), more pectoral-fin rays (15-17 vs. 12-15), and a higher pectoral-fin ratio (0.20-0.31 vs. 0.14-0.22) than B. nyx .

Bothrocara molle is also known throughout the North Pacific, but generally has a higher vertebral count (113-118 vs. 108-116), a more posteriorly placed dorsal fin (anterior pterygiophore usually in fourth interneural space vs. second interneural space), and a lower gill-raker count (18-24 vs. 23-27). Bothrocara molle also attains a much larger maximum size (>550 mm SL) and has a longer snout (longer than orbit vs. shorter than orbit) than B. nyx .

Although Anderson (1994) recognized two species known only from the eastern tropical Pacific, Anderson and Fedorov (2004) recently synonymized one of these ( Bothrocara alalongum ) with B. molle on the basis of Anderson’s unpublished data. The other species, B. elongatum , is currently known only from the two type specimens and one other (Anderson, 1994). It is characterized by a long snout (nearly twice eye length), much higher vertebral count (118-125 vs. 108-116 for B. nyx ), and exserted pectoral-fin rays protruding from the membrane “as a fringe” (Garman, 1899: 130), all of which clearly distinguish it from B. nyx . Furthermore, B. elongatum reaches a maximum size of more than twice that known for B. nyx .

Bothrocara hollandi and B. tanakae were both described by Jordan and Hubbs (1925) from Japan, and both are known only from the western side of the North Pacific, including the Yellow Sea, Sea of Japan, and Sea of Okhotsk (Anderson, 1994). Both species have higher vertebral counts (121 for B. hollandi and 131-133 for B. tanakae vs. 108-116) and lower gill-raker counts (13 for B. hollandi and 16-17 for B. tanakae vs. 23-27) than B. nyx , and B. hollandi has more pectoral-fin rays (17 vs. 12-15). Again, both species attain a much larger maximum size than the largest known specimen of B. nyx .

Anderson (1994) listed three nominal species of uncertain status in this genus ( Bothrocara zesta Jordan and Fowler , Lycogramma soldatovi Schmidt , and Bothrocaropsis rictolata Garman ), suggesting that each is probably a synonym of one of the taxa listed above. Anderson and Fedorov (2004) recently synonymized B. rictolata with B. brunneum , and it is clear that neither of the other species is synonymous with B. nyx . According to Schultz (1967) the holotype of Bothrocara zesta , collected from Sagami Bay in Japan, has 119 vertebrae, which is outside the known range for B. nyx . The holotype of Lycogramma soldatovi has 15 pectoral-fin rays, which is at the upper end of the distribution for B. nyx , and 19 gill rakers, which is well below the lowest gill-raker count observed in B. nyx . Finally, both of these nominal species have the long snout and larger maximum size (>400 mm) typical of this genus, which clearly distinguishes them from B. nyx .

Additional material examined: Bothrocara nyx (specimens not fixed properly in the field, not suitable for designation as types): UW 111806 , 178 mm, 59.354°N, 178.360°W, 966 m depth , collected 13 July 2004 ; UW 111807 , 120 mm, 56.997°N, 173.544°W, 806 m depth , collected 25 July 2004 ; UW 111808 , 5 (135-176 mm), 56.497°N, 172.189°W, 1020 m depth , collected 26 July 2004 ; UW 111809 , 6 (82-115 mm), 56.091°N, 169.197°W, 1130 m depth , collected 27 July 2004 ; UW 111810 , 2 (132-150 mm), 54.482°N, 167.870°W, 1016 m depth , collected 31 July 2004 ; UW 111811 , 8 (117-172 mm), 54.353°N, 167.973°W, 1020 m depth , collected 31 July 2004 ; UW 111812 , 4 (107-122 mm), 54.358°N, 167.848°W, 924 m depth , collected 31 July 2004 ; UW 111813 , 2 (117- 138 mm), 54.306°N, 166.907°W, 1017 m depth , collected 2 August 2004 ; UW 111814 , 15 (103-155 mm), 54.283°N, 167.780°W, 1016 m depth , collected 3 August 2004 .