Zoarcidae Swainson, 1839

Family Zoarcidae Swainson, 1839 View in CoL Genus Gymnelus Reinhardt, 1834

Gymnelus Reinhardt 1834 View in CoL : XXI; 1837a: XXI (reprint).

Gymnelus viridis ( Fabricius, 1780) View in CoL – Common Fish doctor

( Figs 1B View Fig , 2A, C View Fig , 3A–D View Fig )

Ophidium viride Fabricius 1780: 141–142 View in CoL (South-West Greenland, no exact location). [Correct spelling for genus of type species is Ophidion View in CoL ].

Ophidium viride View in CoL : Reinhardt 1830: LIV–LV (branchial rays 6, P 11, D 97).

Gymnelus viridis : Reinhardt 1834: XXI; 1837a: XXI (reprint).

Gymnelis viridis View in CoL : Reinhardt 1837b: 37, 49 (unjustified change in spelling of generic name); Reinhardt 1838: 116, 131 (reprint).

Gymnelus viridis View in CoL : Anderson 1982: 29 (part). – Chernova 1998: 169 (part: ZIN 1945, ZMUC P76169, P761131–32).

Material examined

Neotype ZMUC P761096 View Materials , M 150 mm TL, 146 mm SL; South-West Greenland; coll. M.H. Vahl, registered 24 October 1829 [one of Reinhardt’s specimens].

Other material: 20 specimens 90–213 mm TL, from 9 localities in Greenland. ZIN 1945 (5), 2 FF 196 and 206 mm, 2 MM 192 and 201 mm and juv. 90 mm, South-West Greenland; coll. J.C.H. Reinhardt. – ZMUC P766950 View Materials (1), M 213 mm, Greenland, 11 April 1844 – 22 May 1845. – ZMUC P766951 View Materials – P766954 View Materials (1, 1, 1, 1), FF 103–166 mm, Greenland; no other data. – ZMUC P766955 View Materials , P2397029 View Materials – P2397030 View Materials (1, 1, 1), FF 143 and 132 mm, M 168 mm; Greenland, no other data; registered 6 October 1851. – ZMUC P2397032 View Materials (1), F, – TL, 115 mm SL, South-West Greenland, Egedesminde [now Aasiaat], from Atlantic cod stomach, about 68°43'N, 52°54'W; coll. C.S.M. Olrik; registered 1 July 1861. – ZMUC P2397033 View Materials (1), F 116 mm, Davis Strait, 65°34'N, 54°31'W, R/V “Ingolf”, st 29, 5–18 July 1895, 124 m GoogleMaps

2 Holotype ZMUC 764452 View Materials and paratypes ZMUC P764452 View Materials – P764453 View Materials , P765160 View Materials , P7651778 View Materials – P7651780 View Materials , P7651784 View Materials – P7651785 View Materials ; ZMH Nos 8436 (2), 8437 (4), 8484 (5), 8432 (6), 25459 (4) (number of counts 29) .

See Table 1 for designations.

depth. – ZMUC P2397034 View Materials and P2396751 (1, 1), juv 114 mm, F 165 mm, South Greenland, Julianehaab [now Qaqortoq], Kakarsuak sound, 1 October 1932; coll. R. Bogvad. – ZMUC P761130 View Materials (1), M 205 mm, Julianehaab , ca. 60°45'N, 46°00'W. – ZMUC P761131 View Materials – P761132 View Materials (1, 1), 124 and 128 mm, Julianehaab, May 1902; coll. Mr. Mildorf. GoogleMaps

Etymology. The species name “viridis ” means “green” in Latin, and was given by O. Fabricius due to colour of fishes, which live in a zone of macroalgae.

Diagnosis. Gymnelus with supratemporal pores 2 (1+0+1). Dorsal fin begins above posterior third of pectoral fin, predorsal length 16.5–21.7% (on average 19.1%) TL. Trunk distinctly roundish in cross section. Anterior 4–6 dorsal rays shortened and covered by thick skin. Eye usually less than snout length; gill slit slightly longer than eye diameter. Head short, on average 14.5% TL. Pectoral fin on average less than one-half of head length (47%); base of pectoral fin averaging 43% of fin length. Vertebrae 97–103 (on average 99.6); D 92–99 (95.4), A 77–84 (80.5). Skin without tiny light spots that give illusion of false scales. Length up to 256 mm TL; mature at length of more than 180 mm.

Description

The neotype is a subadult male 150 mm TL ( Fig. 3A View Fig ). Counts and measurements are given in Tables 1 and 2. The maximum body depth is 14.7 times in TL and equal to one-half of the head (49.8% HL). The trunk is roundish; at the pectoral-fin base, the depth-to-width ratio is 1.3, and is the same at the beginning of the anal-fin. The dorsal fin begins above the posterior third of the pectoral fin; the predorsal length is 1.4 times the head length. The anterior 4–6 D -rays are equally shorter than the following ones, and inserted into a thick, rather fleshy fin membrane. The depth of the dorsal and anal fins is less than 1/4 of the body depth. The pectoral fin is rounded, with the base being 42% of the fin length; it inserts close behind the vertical of the opercular-lobe edge.

The head is 7.3 times in TL, its width is slightly less than the head depth. The eye is 6 times in HL; its diameter is less than the snout length. The nostrils are approximately equal to the pupil diameter. The mouth is terminal. The teeth are strong, forming 3 rows in front of each premaxilla; there are 27 teeth in total (16/5/6). The dentary teeth are arranged in two rows of 27 (21/6). The number of teeth is 6 on the vomer and 10 and 12 on palates (each in two rows, 9/1 and 9/3). The end of the upper jaw extends slightly behind the posterior edge of the eye. The palatine respiratory membrane is wide, extending to the teeth of the vomer. The width of the upper lip is 2/3 of the eye diameter; the lower lip is interrupted (attached) anteriorly. The gill slit is slightly longer than the eye diameter and reaches down the level of the upper third of the pectoral-fin base. The opercular flap is rounded; on the body beneath it there is a thin and shallow skin fold that closes tightly the gill opening. The sensory system has an interrupted supratemporal commissura; there are 2 supratemporal pores (1+0+1). Other pores: there are 2 nasal, 7 infraorbital (8 on the right side of the head as one pore with a double opening), 8 preoperculo-mandibular, and 4 temporal (1+3) pores. The lateral line consists of superficial neuromasts on the anterior part of the body.

Variability. In adult specimens (192–213 mm TL), specific characters are more pronounced ( Fig. 3B View Fig ). The trunk is distinctly roundish in cross-section; the depth-to-width ratio above the pectoral-fin base is 1.2 on average. The depth of the body increases posteriorly; on average, it is 50.6% HL at the occiput, 51.8% above the pectoral fin and 55.2% above the anal-fin origin. The depth of the unpaired fins is less than 1/3 of the body depth. The anterior portion of the dorsal fin is lower than the rest of the fin, with a rather thick fin membrane, almost not emarginated at ray tips. SL = 0.975 TL.

The head is small, on average 14.5% TL, its width is less than the head depth. The eye diameter is shorter than the snout ( Fig. 3C View Fig ); the gill slit is slightly longer than the eye. The gill slit reaches the level of the upper third of the pectoral-fin base. The upper jaw teeth are in 3 rows, 14–19 in total number (11 – 17/3 – 7/2 – 8); the teeth of the outer row are large and even. The lower jaw teeth form two rows, 11–27 (9 – 17 / 2 – 6). The teeth number on the vomer is 4 – 7, on the palate 5 – 10. The pseudobranchia consists of 7 filaments, sitting in one row; the number of gill rakers on the 1st arch (outer and inner sides) is 6 and 9 (counted in one specimen). The sensory system has an interrupted supratemporal commissura; there are 2 supratemporal (1+0+1), 2 nasal, 4 temporal (1+3), 6–8 infraorbital, and 7–8 preoperculo-mandibular pores (there may be double openings of some pores).

Radiographs. D 92–99, A 77–84. D +1/2 C 98–105, A +1/2 C 81–93. Vertebrae 97–103: abdominal 19–21 and caudal 77–83. Vertebrae without ribs 2–3. Dorsal rays in precaudal part 15–19. First dorsal-fin ray inserted between processes of vertebrae 2–5; rayless pterygiophores in front 0–3. Anal-fin rays before first haemal spine 2–3. Caudal fin consists of 9–11 rays, including 7–9 (3–4 / 3–5) primary rays (usually 4/4), 1–2 upper secondary and 0–2 lower ones.

Allometry. The eye decreases with the body size, accounting for 23.3–24.7% HL in specimens 90–143 mm TL and 17.9–19.6% in specimens 192–206 mm TL. The upper jaw usually does not extend to the vertical of the posterior edge of the eye in individuals TL <150 mm (both sexes), and reaching further in larger fish. In juveniles of 55–98 mm, the gill slit is longer than in adults, reaching to the mid-level of the pectoral-fin base (rarely to the 6–9th P -fin ray, counting from above).

Sexual dimorphism . Like other Gymnelus , males have a longer upper jaw than females, extending beyond the eye. The cheek muscles are somewhat swollen; the dorsal muscles behind the occiput are better developed, enlarged ( Fig. 3B, C View Fig ).The anal-fin membrane in females is always pale, and in males it is blackish along the edge (even if they are immature).

The color of live fishes was greenish, which is reflected in the Latin name. Skin of the museum specimens is uniform without fine speckles (both sexes). The peritoneum and orobranchial cavity are pale. Ocelli may be present on the dorsal fin, usually 1 or 2, and are more common in males. The smallest specimens (females 98 and 116 mm TL) have signs of juvenile color with 10 to 17 vertical uniform dark stripes on the body and tail.

Size. In our series, the length of males reaches 213 mm and that of females 206 mm TL. The maximum recorded size is 256 mm TL ( Anderson 1982).

Distribution. The specimens were collected from the coastal waters of Greenland, in the south (Qaqortoq, approximately 60°45'N, 46°00'W) and in the southwest: in the Davis Strait near the shore (65°17'N, 54°17'W) and in Aasiaat (approximately 68°43'N, 52°54'W) ( Fig. 4 View Fig ). The maximum depth of collection is 101 m.

The wide distribution of “ G. viridis ”, shown by E. Anderson (1982), is based on a mixture of species, including those from the Pacific Ocean with three supratemporal pores of the sensory system.

Biology. This fish lives close to shore in a zone of macroalgae. The body shape with strong neck muscles, low at the occiput and increasing in height posteriorly, as well as the presence of thick skin covering the front of the dorsal fin, suggest that it may live among and under stones.

Spawning may occur in the fall, as a mature female 165 mm TL, caught in early October in Julianehaab (Kakarsuak sund) ( ZMUC P2396751 View Materials ), has 78 eggs in the ovaries with a diameter of 4–5 mm .

One of our specimens was found in the stomach of an Atlantic cod, but G. viridis is unlikely to be abundant enough to be an important food for it.

Comparisons. In the Eastern North Atlantic and adjacent Arctic, there are other Gymnelus , which belong to the “two-pore” group. Gymnelus knipowitschi differs from G. viridis in fewer vertebrae (88–94 versus 97–103), in the anterior position of the beginning of the D -fin (above the first third as compared to the last third of the P -fin), the absence of shortened rays on the first part of the D -fin ( Fig. 5A View Fig ) (present in G. viridis ) and other characters ( Chernova 1999a).

The second species, G. esipovi , differs from G. viridis by a more posterior location of the dorsal fin origin ( Fig. 5B View Fig ), the first ray inserted between 5/6 to 8/9 vertebrae vs. 2/3 to 5/6 vertebrae in G. viridis , longer predorsal length (21.2–25.1% vs. 16.5–21.7% SL), and larger eye (22–26% HL vs. 16.6–24.7%). In addition, G. esipovi is a small-sized species: the maximum length of mature adults does not exceed 132 mm (females of G. viridis are immature at this length, reaching a twice-longer size – 256 mm).

Our understanding of G. viridis is narrower than that of E. Anderson (1982), since he did not use the type of supratemporal commissure as a diagnostic character. In our opinion, his “ G. viridis ” is based on a mixture of species, including those from the Pacific Ocean with three supratemporal pores.

Taxonomic notes. The name Ophidium stigma Lay et Bennett, 1839 (= Gymnelus stigma ) usually is included in synonymy of G. viridis . The species had been described from Kotzebu Sound (Alaska, Chukchi Sea). The type was not preserved. The characters in the description are scarce ( Lay and Bennett 1839: 67, tab. 20, fig. 1). However, it can be concluded that the fish may belong to the subfamily Gymnelinae Gill, 1863 , because the pelvic fins are absent and D and A overlay the caudal fin. The questionable detail is the presence of scales (“scales were very small”), while the skin of all Gymnelus is naked. This character was ignored when the species was included in the synonymy of G. viridis . It is more likely that O. stigma may belong to the related genus Gymnelopsis (subfamily Gymnelinae ), which includes six scaly species: G. brashnikovi Soldatov, 1922, G. brevifenestrata Anderson, 1982 , G. ocellata Soldatov, 1922 , G. humilis Nazarkin and Chernova, 2003 , G. Japonica (Katayama, 1943) and G. ochotensis (Popov, 1931) ( Fricke et al. 2020) . The conclusion is that Ophidium stigma ( Gymnelus stigma ) should be excluded from the synonymy of G. viridis .