Gobio nigrescens ( Keyserling, 1861 )

Mousavi-Sabet, Hamed, Ganjbakhsh, Babak, Geiger, Matthias F. & Freyhof, Jörg, 2016, Redescription of Gobio nigrescens from the Hari River drainage (Teleostei: Cyprinidae), Zootaxa 4114 (1), pp. 71-80 : 73-78

Gobio nigrescens ( Keyserling, 1861)

( Figs. 3–6 )

Bungia nigrescens Keyserling, 1861:18 , Plate. VIII Material examined. VMFC G1304, 9, 65–95 mm SL; FSJF 3519, 2, 75–81 mm SL; Iran: Khorasan-e-Razavi prov.: Hari River at Pol-e-Khatoun, 35°57'39.19"N 61°6' 58.813"E; H. Mousavi-Sabet, B. Ganjbakhsh & A. Jouladeh, 20 Nov 2013. Genbank accession numbers: KU647814 , KU647815 .

Diagnosis. Gobio nigrescens is distinguished from G. lepidolaemus , which is the only geographically close species, by having a naked breast (vs. covered by scales), more scale rows on the caudal peduncle (½3/1/3½ vs. ½2/1/2½), 16 circumpeduncular scales (vs. 12–14), more predorsal scales (16–18 vs. 14–16), more scale rows between the lateral line and the pelvic-fin origin (4½ vs. 3½), more irregularly shaped, black or brown blotches on back behind dorsal-fin base (6–7 vs. 2–4 blotches, usually no blotches on back behind dorsal-fin base) and a more slender caudal peduncle (caudal peduncle depth 2.4–2.9 times in its length vs. 1.7–2.2).

Description. See Figures 3–6 for general appearance and Table 1 for morphometric data of five individuals. A medium sized, moderately short headed and moderately elongate species. Greatest body depth at or slightly in front of dorsal-fin origin, decreasing strongly below dorsal-fin base, slightly decreasing towards caudal-fin base. Body and caudal peduncle strongly compressed. Caudal peduncle 2.4–2.9 times longer than deep. Snout short and blunt in some individuals, longer in others. Eye 1.5–1.6 times in snout length and 1.4–1.6 times in interorbital distance. Interorbital space flat in medium-sized specimens to markedly concave in larger ones. Dorsal-fin margin slightly concave. Pectoral fin triangular with slightly concave posterior margin, reaching about middle of distance between pectoral- and pelvic-fin base. Pelvic-fin origin at a vertical between first and second branched dorsal-fin ray. Pelvic fin rounded, reaching about half of distance between anus and anal-fin origin. Two pelvic axillary scales. Caudal fin deeply forked, with rounded lobes, upper lobe usually longer than lower lobe. Longest ray in upper lobe 1.5–1.7 times longer than middle caudal-fin ray. Largest recorded specimen 95 mm SL.

Dorsal fin with 3 simple and 7½ branched rays. Anal fin with 3 simple and 5½ branched rays. Caudal fin with 9+8 branched rays. Pectoral fin with 14–15 rays and pelvic fin with seven rays. Body covered by scales. No scales on pectoral-fin base and on breast in front of a line connecting the base of the left and right last pectoral-fin ray ( Fig. 6 ). 39+2 (4) or 40+2 (1) scales along lateral line, 16–18 irregularly set predorsal scales, ½3/1/3½ scale rows on caudal peduncle and 16 circumpeduncular scales, 4½ scale rows between lateral line and pelvic-fin origin and 4½ scale rows between lateral line and anal-fin origin. Four scale rows between anus and anal-fin origin. Barbel reaching vertical through middle of eye. Mouth strongly arched. Postlabial groove broadly interrupted medially. Upper lip thin, lower lip swollen, with a constriction at level of interruption of postlabial groove defining a lateral lobe on each side ( Fig. 6 ).

Colouration. Background colour olive-brown to silver in live and yellowish brown in preserved specimens. Top of head dark grey with an irregular black or brown pattern. Side of head brownish grey, brown or yellowish with an irregularly shaped dark-brown field of pigments on opercule. A short, black stripe under eye and between anterior eye margin and tip of snout. Back with a greyish, mottled pattern. Behind dorsal-fin base, 6–7 irregularly shaped black blotches on back. Flank with 9–11 roundish or horizontally elongated black blotches, slightly faded in front of dorsal-fin base, bold on flank behind dorsal-fin base. On flank, scales with more pigment cells on upper and lower part, less pigmented in middle, forming faint and irregularly shaped narrow stripes, especially on flank above lateral line. On flank below lateral line, usually more pigment cells in scale pocket and along posterior margin of exposed part of scales, forming zig-zag lines. Lateral-line scales with a small brown or black blotch above and below lateral line forming two longitudinal rows of spots.

Ventral surface of head, belly and caudal peduncle whitish or yellowish without colour pattern. Lips and barbels whitish. Pectoral and pelvic fins yellow-orange in live, other fins hyaline. All fins hyaline in preserved individuals. Dorsal, caudal and pectoral fins with dark brown, elongated blotches on rays forming 5–7 irregularly shaped bands. Pelvic and anal fins without colour pattern.

Distribution. Gobio nigrescens is found in the Hari River in Afghanistan, Iran and Turkmenistan.

Remarks. The Hari River is situated at the southern border of the distribution range of the genus Gobio and a close relationship of G. nigrescens to G. lepidolaemus from the adjacent Aral Sea basin was expected prior to this study. Our molecular data do not support such a relationship and also no close relationship to any of the other Gobio species found in the wider neighbourhood of the Hari River. It has to be mentioned that the freshwater fishes of the Aral Sea basin as well as of other parts of Central Asia and Siberia are still incompletely studied and it is well possible that more than one Gobio species would occur in the Aral Sea basin. More, and geographically dense studies, including fishes from the type localities of G. lepidolaemus (Serafshan [Zarafshan] River drainage in Uzbekistan; Syr-Darya River at Chodshent [Khujand] in Tajikistan) and G. nikolskyi (Amu-Darya River, Uzbekistan), which is treated as a subspecies of G. gobio by Kottelat (1997), are needed to better understand the taxonomy and also biogeography of these fishes.

Figures

FIGURE 3. Gobio nigrescens, VMFC G 1304, 95 mm SL; Iran: Hari River.

FIGURE 4. Gobio nigrescens, VMFC G 1304, lateral view, from top to bottom: 87 mm SL, 81 mm SL, 73 mm SL, 65 mm SL; Iran: Hari River.

FIGURE 5. Gobio nigrescens, VMFC G 1304, dorsal view, from top to bottom: 95 mm SL, 87 mm SL, 81 mm SL, 73 mm SL, 65 mm SL; Iran: Hari River.

FIGURE 6. Gobio nigrescens, VMFC G 1304, 95 mm SL; ventral and dorsal views of head.

Tables

TABLE 1. Morphometric data of Gobio nigrescens. (VMFC G 1304, n = 5)

Standard length (mm)	95.2	86.6	80.9	72.7	65.3
In percent of standard length
Head length	23.8	22.3	25.8	25.2	24.8
Body depth at dorsal-fin origin	22.6	20.5	22.3	21.7	20.9
Body width at dorsal-fin origin	17.3	17.4	18.7	17.7	17.9
Predorsal length	45.4	45.3	43.3	43.4	43.9
Prepelvic length	46.4	47.5	50.7	48.5	48.8
Preanal length	69.1	67.7	67.7	67.1	68.2
Head depth	16.5	15.5	16.9	16.2	16.3
Caudal peduncle depth	8.8	8.3	9.3	8.5	9.0
Caudal peduncle length	21.0	24.0	23.0	23.6	22.5
Last simple dorsal-fin ray length	19.9	20.5	20.6	20.1	20.0
Anal-fin depth	16.4	16.7	16.9	17.0	16.9
Pelvic-fin length	15.7	15.9	15.7	15.9	15.8
Pectoral-fin length	17.2	18.5	19.5	18.6	18.4
Upper caudal-fin lobe length	16.7	19.5	19.6	19.0	19.2
Middle caudal-fin ray length	9.8	12.1	13.1	11.5	12.0
In percent of head length
Head depth at nape	69	69	65	65	66
Eye diameter	28	25	22	24	24
Snout length	37	40	35	35	36
Interorbital width	40	41	34	35	34