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A recent record of Romanogobio antipai (Actinopterygii, Cyprinidae, Gobioninae) from the Danube River in Bulgaria
expand article infoNina G. Bogutskaya, Tihomir Stefanov§, Alexander M. Naseka, Oleg A. Diripasko|
‡ Naturhistorisches Museum Wien, Vienna, Austria
§ National Museum of Natural History, Sofia, Bulgaria
| Institute of Fisheries and Marine Ecology, Berdyansk, Ukraine
Open Access

Abstract

The Danube delta gudgeon, Romanogobio antipai, has been considered to be extinct because there were no reliable recent observations. The latest record confirmed by a voucher specimen dating from 1992. We report here on a specimen of R. antipai collected in 2016 in the Bulgarian sector of the Danube main stream using a bottom drift net at a depth of 8 m. The species determination is supported by morphological examination including discriminant and cluster analyses in comparison with three syntypes and five non-type specimens of R. antipai, samples of the R. kesslerii species complex and R. vladykovi. Romanogobio antipai most clearly differs from both R. kesslerii and R. vladykovi by proportional measurements (caudal peduncle depth, head width, eye horizontal diameter, and interorbital width), from R. kesslerii also by the number of scales above and below the lateral line (6 and 4, respectively, (vs. commonly 5 and 3), and from R. vladykovi, also by 8½ branched dorsal-fin rays (vs. 7½) and the vertebral caudal region longer than the abdominal vertebral region (abdominal+caudal vertebrae 19+21 or 20+21, vs. commonly 20+20 or variants with a caudal region shorter than the abdominal one). The possibility that R. antipai represents a deep-water cophenotype of either R. kesslerii or R. vladykovi, cannot be excluded. The new record demonstrates that R. antipai is still extant in the lower Danube but may be restricted to greater depths in the main channel and the deltaic branches.

Keywords

Danube delta gudgeon, morphology, meristics, distribution, conservation status

Introduction

Romanogobio Bănărescu, 1961 is a genus of bottom-dwelling, rheophilic gudgeons with a wide distribution in temperate Eurasia. Six species were reported from the Danube basin (Kottelat and Freyhof 2007, Friedrich et al. 2018). Among them, Romanogobio antipai was described, as Gobio kessleri antipai, by Bănărescu (1953: 300, 318) based on a series of syntypes from the Danube delta at Sulina (12 specimens collected by Grigore Antipa before 1909) and the lower reaches of the Danubian tributary Argeş (one specimen collected by Băcescu). In the same paper, representing a study of morphometric features within the “Gobio kessleri” group of populations distributed in Romania, Bănărescu also recognized a new form, Gobio kessleri kessleri natio banaticus (the name is not available from this publication, but available as Gobio kessleri banaticus from Bănărescu 1960: 121) and compared both new forms with the nominotypical subspecies. As the correct original spelling of the specific name is kesslerii (Kottelat 1997), we use it hereafter.

Bănărescu (1953) distinguished Romanogobio antipai from R. kesslerii and R. k. banaticus on average values of the postorbital distance (10.5% of body length vs 8.5–10%), barbel length (10.5–13% of body length vs 8–11.5%), eye diameter (5.5% of body length vs 5.6–6.4% R. excluding kesslerii (Dybowsky, 1862) from Bulgaria with 4.8–5.6%, and 75.2% of interorbital distance vs 81.9–98.5%), snout length (9.4% of body length vs 9.4–11.7%), and maximum body depth (18.4% of body length vs 1.8–17.7% excluding R. kesslerii from the Dniester with an average of 18.5%). Consequently, no clear differences between the three taxa were presented, and later Bănărescu (1960, 1961) reported the occurrence of specimens morphologically intermediate between R. antipai and R. kesslerii in the Danube tributaries Ialomiţa, Argeș (Dâmboviţa) and Siret (Bizau and Milcov Rivers), recognized as such also by Bănărescu and Nalbant (1973). Bănărescu (1961, 1999: 151) repeated the most typical features of R. antipai from the Danube delta (smaller eye and deeper body), adding smaller body length in adults (“apparently not exceeding 6 cm”), commonly 4 scales (vs commonly 3) between the lateral line and the pelvic-fin origin, caudal-peduncle width at the anal-fin origin commonly about equal to caudal-peduncle depth (vs larger in kesslerii), and short lateral blotches (vs commonly elongated in banaticus). The distribution range was widened (Bănărescu 1961: 344) to include the lower reaches of the Siret River and its tributaries, the Milcov, Putna, and Birlad Rivers, and the lowest reaches of the Argeş and Ialomiţa Rivers. Similar data were later published in the book on the fishes of Romania (Bănărescu 1964: 454–455, fig. 195).

Bănărescu (1992, 1994a, 1999: 150, fig. 21) again restricted the range of R. antipai to the lowest reaches of the Danube, mentioning that before 1959, it was distributed upstream to the Argeş River mouth (some 430 river kilometres). He emphasized that it markedly differed from other members of the R. kesslerii complex by its morphological features, which were related to dwelling in deep water of the main stream of the river.

Bănărescu (1992, 1994a, 1999) treated the Danube delta gudgeon as a subspecies (Gobio kesslerii antipai) but mentioned that it deserved the rank of species. Kottelat and Freyhof (2007) considered it as a valid species and Friedrich et al. (2018) found no arguments to reject this status.

The sample of Romanogobio antipai from the Danube delta at Sulina, described by Bănărescu based on G. Antipa’s collections (before 1909) was not the only one from the Danube delta. Smirnov (1971) provided meristic and morphometric data on a sample of 24 specimens collected by him in April 1961 in the Ukrainian part of the delta (Chilia Arm) near Izmail and identified it as R. kesslerii. This sample was later included in the book on Ukrainian fishes by Movchan and Smirnov (1981: 344, tab. 181). Bănărescu (1999: 158) suggested that Smirnov’s (1971) specimens from Izmail belonged to R. antipai because they had a deeper body and a smaller eye.

The most recent published record of R. antipai from the lower section of the Danube may be that of Marinov (1978) who reported Gobio kesslerii from the main course of the Danube in Bulgaria. The true R. kesslerii only occurs in middle reaches of tributaries and has not been recorded from the deep main stream of the Danube (e.g., Chichkoff 1937, Mihailova 1970, Dikov et al. 1994).

The absence of recent records of R. antipai lead some authors to the conclusion that the species might be extinct (Bănărescu 1994b, Kottelat 1997). Its conservation status was later evaluated as extinct (Kottelat and Freyhof 2007, Freyhof and Kottelat 2008) because it was supposed that all known ichthyological surveys conducted since the 1960s to 2003 in suitable habitats in the Danube delta had failed to find it; however, this statement is not entirely correct as there is a specimen in Natural History Museum ‘Grigore Antipa’ collected in 1992 (described below).

In 2016, TS collected a gudgeon specimen in the Bulgarian sector of the Danube main stream using a bottom drift net at a depth of 8 m, near the village of Vetren (river kilometer 395). This specimen (Figs 12) was preliminarily identified by AN as Romanogobio antipai because of its small eye and 8½ branched dorsal-fin rays distinguishing it from both R. kesslerii and R. vladykovi (Fang, 1943). The present note is devoted to a comparative description of the specimen to test this hypothesis.

Figure 1. 

Lateral view of Romanogobio antipai NMNHS specimen 68.7 mm SL, Danube at Vetren (a) MGAB/BN760 specimen 64.9 mm SL, lower Argeş R. (b) ANSP syntype 47.8 mm SL, Sulina (c) and R. kesslerii NMNHS, 65.7 mm SL, Tsibritsa River (d).

Figure 2. 

Dorsal view of the head of Romanogobio antipai, NMNHS specimen 68.7 mm SL, Danube at Vetren (a) MGAB/BN759, SL 47.7 mm, Sulina (b) ANSP syntype 47.8 mm SL, Sulina (c) and R. kesslerii NMNHS, 65.7 mm SL, Tsibritsa River (d).

Material and methods

Methods for counting fin rays and scales, and for measurements, follow Kottelat and Freyhof (2007) except that head length, postorbital length, and interorbital width include the skin fold. In the examined samples, standard length is used for some relative measurements. Body length, which is the length to the posterior margin of the posterior-most scale on the base of the caudal fin (called standard length II by Holčík et al. (1989: fig. 12), is also measured and the data are compared for diagnostic characters taken from the literature. All measurements were made point-to-point with a dial caliper and recorded to the nearest 0.1 mm. Vertebral counts taken from radiographs follow the scheme by Naseka (1996). To avoid probable discrepancy in lateral-line count, we provide not only the number of lateral-line scales to the posterior margin of the hypurals but also numbers of total lateral scales and total lateral-line scales. Statistical analyses were done using Microsoft Excel, Statistica 6.0 (Statistic for Windows. Statsoft; Discriminant Functional Analysis, DFA), and SPSS Statistics V23.0 (IBM SPSS; Cluster Analysis, CA).

Abbreviations

ANSP, Academy of Natural Sciences, Philadelphia, USA; NB, Bănărescu Nalbant Ichthyology Collection (now in Muzeul de Istorie Naturala ‘Grigore Antipa’); ICBB, Institutui of Stiinte Biologice, Bucharest, Romania; IUCN, International Union for Conservation of Nature; MGAB, Muzeul de Istorie Naturala ‘Grigore Antipa’, Bucharest, Romania; NMNHS, National Museum of Natural History, Sofia, Bulgaria; NMW, Naturhistorisches Museum Wien, Vienna, Austria. BL, body length; HL, lateral head length; rkm, river kilometer; SD, standard deviation; SL, standard length.

Material examined

We specifically selected for comparison mostly those specimens of R. kesslerii that were donated and/or identified by Petru Bănărescu and followed his original descrimination of the forms within the R. kesslerii species complex. Specimens of Romanogobio vladykovi were selected from localities geographically close to Bulgaria and of a comparable length range.

NMNHS [no number], SL 68.7 mm, Bulgaria: Danube near Vetren, 395 rkm, 44.142637N, 27.029662E, 8 July 2016, coll. T. Stefanov.

Romanogobio antipai. All from Romania. Type material: MGAB 49908 (as Gobio kessleri antipai), 1, SL 46.2 mm, labelled as holotype, Romania: [Danube at] Sulina, before 1909, leg. G. Antipa; MGAB (ISBB 0519), 1, SL 50.8 mm, labelled as paratype, same data as MGAB 49908; ANSP 98961 (as Gobio kessleri antipai), 1, SL ca. 47.8 mm, labelled as paralectotype (misspelled as lectoparatype), same data as MGAB 49908, don. P. Bănărescu as paratype; non-type: MGAB (ISBB 0714, BN760, as Gobio kessleri antipai), 3, SL 64.9, 28.6 and 26.2 mm, Romania: lower Argeş River at Olteniţa, 26 July 1961, coll. and det. P. Bănărescu; MGAB (BN759, as Gobio kessleri antipai), 1, SL 47.7 mm, Romania: Sulina Branch, ”27–28th miles”, Danube delta, Oct. 1992; MGAB (ISBB 3567, BN758, as Gobio kessleri antipai), 1, SL 30.1 mm, Romania: Saint Gheorghe Branch, Danube delta, no date, coll. V. Leonte. ANSP 98961 was examined on photos (lateral, dorsal, and ventral aspects) and an X-radiograph.

Romanogobio banaticus (but see Friedrich et al. 2018: 346 on R. carpathorossicus (Vladykov, 1931) as senior synonym of this species). NMW 65539, 30, SL 31.1–7.9 mm, Romania: Timiş at Urseni, Timişoara, 6 Sept. 1962, don. and det. P. Bănărescu as Gobio kesslerii banaticus.

Romanogobio kesslerii s.l.. NMW65532, 12, SL 33.3–57.9 mm, Romania: Tur at Turulung, northeast of Satu-Mare, 5 Sept. 1963, don. and det. P. Bănărescu, as intermediate between Gobio kesslerii kesslerii and Gobio kesslerii banaticus; NMW 65538, 9, SL 39.4–74.7 mm; Romania: Milcov at Focsani, Moldau, 14 Sept. 1963, don. and det. P. Bănărescu as Gobio kessleri antipai with a comment: “not very typical”, as Gobio kessleri kessleri in Bănărescu (1999: 146); NMNHS [no number], 10, SL 55.1–66.5 mm; Bulgaria: Tsibritsa River [right tributary to Danube, NW Bulgaria] near Yakimovo, 43.62245N, 23.33022E, 18 July 2012, coll. T. Stefanov.

Romanogobio kesslerii kesslerii. NMW 60250, 6, SL 50.1–61.2 mm; Romania: Areş River at mouth of Mureş, Transsylvania, 2 Oct.1949, don. and det. P. Bănărescu (in Gobio); NMW 65535, 4, SL 50.6–61.5 mm; Romania: Bereteu at Roşiori-Bihor, north of Oradea, 4 Sept. 1963, don. and det. P. Bănărescu (in Gobio); NMW 90883, 2, SL 85.3–91.2 mm; Ukraine: Smotrich River at Kamenetz Podol’ski [Dniester drainage], 7 May 1921, det. P. Bănărescu, 1991 (in Gobio).

Romanogobio vladykovi. NMW 53356, 2, SL 76.7–81.4 mm; Serbia: Nisch [Niš, Great Morava-Danube], Dec. 1894; NMW65537, 20, SL 46.4–81.4 mm; Romania: Timiš River at Peciu Nou [Danube drainage], 28 Aug. 1863; NMW 60234, 2, SL 73.2–77.2 mm; Romania: Bega R. [Danube drainage], Banat, Sept. 1943.

Results

General appearence of the NMNHS presumed R. antipai specimen from the Danube at Vetren is shown in Figs 12 together with a syntype and a non-type R. antipai specimen in comparison to R. kesslerii and R. vladykovi. Counts, descriptive states of the pectoral-fin length, and measurements are presented in Tables 1, 2. Examined character states in this specimen coincide considerably with those in the three type specimens of R. antipai and five non-type specimens, and demonstrate its differences from the samples of both the R. kesslerii species complex and R. vladykovi. As the standard length averages 96.8% of the BL (calculated in the Romanogobio material examined in this study), the difference between relative measurements (in % SL and in % BL) is slight and the morphometric character states that have been considered as diagnostic for R. antipai vs. R. kesslerii are confirmed. They include maximum body depth, 19–25% SL (17–25.5% of BL; in parentheses, data from Bănărescu (1953, 1961, 1999) and Movchan and Smirnov (1981) are summarized); caudal peduncle depth, 8–9% SL (7–9% of BL) and 35–38.5% of caudal peduncle length; eye diameter, 5–6% SL (5–6% of BL), 20–23% HL (18–24% HL), and 59–68.5% of interorbital width (61–81% of interorbital width). The NMNHS specimen has 6 and 4 scales, respectively, above (to the dorsal-fin origin) and below (to the pelvic-fin origin) the lateral line similar to the three type specimens of R. antipai and the topotypical specimen from Sulina thus confirming the opinion (Kottelat and Freyhof 2007, Friedrich et al. 2018) that this character is one of the most dependable diagnostic characters for the species. All other counts are identical or very close in the NMNHS specimen and R. antipai examined in this study (Table 1). None of the R. antipai specimens had 7½ branched dorsal-fin rays thus confirming its main difference from R. vladykovi characterized by 7½ branched dorsal-fin rays (Naseka et al. 1999; Naseka 2001).

Meristic data for examined specimens of Romanogobio antipai and R. kesslerii species complex.

Dorsal-fin branched rays Anal-fin branched rays Pectoral fin relative to pelvic-fin origin Scales between lateral line and dorsal-fin origin Scales between lateral line and pelvic-fin origin
not reaching almost reaching reaching behind 5 6 2 3 4
R. antipai MGAB 49908 syntype 1 1 1 1 1
R. antipai MGAB/ISBB 0519 syntype 1 1 1 1 1
R. antipai ANSP 98961 syntype 1 1 1 1 1
Non-type MGAB R. antipai, n=5 5 1 4 1 5 5
Presumed R. antipai NMNHS specimen 1 1 1 1 1
R. k. kesslerii. NMW 60250, 65535. Danube drainage, n=10 10 10 7 1 2 10 10
R. k. kesslerii. NMW 908803, Dniester drainage, n=2 2 2 2 2 2
R. banaticus. NMW 65539, Danube drainage, n=30 27 3 30 26 3 1 29 1 30
R. kesslerii s.l. NMW 65532, NW Romania, n=12 12 12 6 1 5 12 1 11
R. kesslerii s.l. NMW 65538, NE Romania, n=9 8 1 6 3 5 3 1 9 9
R. kesslerii s.l. NMNHS, NW Bulgaria, n=10 10 10 10 6 2 1 1 10 10
R. vladykovi NMW 53356, 60234, 65537, Danube drainage, n=24 24 24 24 10 14 15 9

Continued.

Predorsal abdominal vertebrae Abdominal vertebrae Pre-anal caudal vertebrae Caudal vertebrae Total vertebrae
10 11 18 19 20 21 2 3 4 19 20 21 38 39 40 41 42
R. antipai ANSP 98961 syntype 1 1 1 1 1
Non-type MGAB R. antipai, n=5 2 3 4 1 3 2 5 4 1
Presumed R. antipai NMNHS, n=1 1 1 1 1 1
R. k. kesslerii NMW 60250, 65535. Danube drainage, n=10 2 8 1 8 1 7 3 3 5 2 2 7 1
R. k. kesslerii NMW 908803, Dniester drainage, n=2 2 2 2 2 2
R. banaticus. NMW 65539, Danube drainage, n=30 9 21 26 4 4 21 5 2 19 8 1 18 10 2
R. kesslerii s.l. NMW 65532, NW Romania, n=12 1 11 7 5 5 7 1 7 4 4 8
R. kesslerii s.l. NMW 65538, NE Romania, n=9 1 8 3 6 4 5 1 5 3 1 8
R. kesslerii s.l. NMNHS, NW Bulgaria, n=10 10 2 8 2 8 2 8 4 6
R. vladykovi Danube drainage, Romania and Ukraine, n=46 (from Naseka 2001). 9 37 4 38 4 12 46 8 4 29 12 3 31 11 1
R. vladykovi NMW 53356, 60234, 65537, Danube drainage, Romania and Serbia, n=24 3 21 19 5 12 12 5 15 4 2 16 6

Continued.

Total lateral-series scales Total lateral-line scales Lateral-line scales to posterior hypural margin
39 40 41 42 43 44 39 40 41 42 43 37 38 39 40 41 42
R. antipai MGAB 49908 syntype 1 1 1
R. antipai MGAB/ISBB 0519 syntype 1 1 1
R. antipai ANSP 98961 syntype 1 1 1
Non-type MGAB R. antipai, n=5 1 3 1 2 3 1 1 2 1 1
Presumed R. antipai NMNHS, n=1 1 1 1
R. k. kesslerii NMW 60250, 65535. Danube drainage, n=10 3 4 3 1 2 5 2 2 2 5 1
R. k. kesslerii NMW 908803, Dniester drainage, n=2 1 1 1 1 1 1
R. banaticus NMW 65539, Danube drainage, n=30 8 9 3 1 8 9 2 4 6 9 1
R. kesslerii s.l. NMW 65532, NW Romania, n=12 2 4 6 4 3 5 2 2 6 2
R. kesslerii s.l. NMW 65538, NE Romania, n=9 7 2 3 4 2 3 4 2
R. kesslerii s.l. NMNHS, NW Bulgaria, n=10 6 3 1 2 5 2 1 6 4
R. vladykovi NMW 53356, 60234, 65537, Danube drainage, Romania and Serbia, n=24 1 7 5 10 1 1 8 6 8 1 1 9 8 6

Measurements and counts for examined specimens of R. antipai, R. kesslerii and R. vladykovi. Gap between ranges or ranges only slightly overlapping: * between R. antipai and R. kesslerii, ** between R. antipai and both R. kesslerii and R. vladykovi, *** between R. antipai and R. vladykovi; **** no statistical difference; remaining characters display statistically significant differences (Kruskal-Wallis test, p<0.01) but ranges overlapping.

Characters R. antipai n=6 R. kesslerii n=26 R. vladykovi n=22
R. antipai NMNHS min max Mean SD min max Mean SD min max Mean SD
SL, mm 68.67 46.20 68.67 54.44 9.743 45.11 74.69 59.53 5.776 46.39 81.42 60.21 10.310
Body depth at dorsal-fin origin (% SL)* 25.43 18.56 25.43 20.37 2.671 15.59 18.63 16.88 0.834 17.50 23.00 19.20 1.277
Depth of caudal peduncle (% SL)* 9.20 8.13 9.20 8.49 0.388 6.33 7.67 7.04 0.358 8.30 10.15 9.06 0.416
Depth of caudal peduncle (% length of caudal peduncle)** 38.47 34.80 38.47 36.72 1.416 24.90 33.44 30.23 2.599 39.32 49.69 44.12 3.117
Predorsal length (% SL) 46.56 44.43 46.56 45.57 0.832 43.41 49.32 46.73 1.415 46.29 49.40 47.57 0.949
Postdorsal length (% SL) 41.90 37.29 41.90 39.89 1.945 39.56 47.49 43.91 1.884 39.48 43.83 41.56 1.432
Prepelvic length (% SL) 48.89 47.76 50.60 48.79 0.989 44.79 49.78 47.45 1.218 48.41 52.79 50.65 1.423
Preanal length (% SL) 70.21 69.60 72.20 70.74 0.875 67.12 73.01 69.91 1.653 69.90 76.28 73.23 1.181
Pectoral – pelvic-fin origin length (% SL) 23.92 22.95 24.60 23.88 0.650 21.15 25.42 23.51 0.865 23.29 27.32 25.58 1.423
Pelvic – anal-fin origin length (% SL) 23.13 21.70 23.13 22.17 0.535 18.66 24.84 21.55 1.374 20.12 24.59 22.86 1.080
Caudal peduncle length (% SL) 23.93 22.61 24.00 23.15 0.632 20.21 29.11 23.80 2.502 18.68 22.98 20.63 1.440
Pectoral-fin length (% SL) 23.18 22.05 23.18 22.55 0.440 19.69 24.00 22.20 1.320 18.49 22.89 20.75 1.162
Pelvic-fin length (% SL) 19.67 17.52 19.67 18.54 0.732 16.13 19.10 17.94 0.743 14.22 18.69 16.35 1.266
Head length (% SL)**** 25.99 24.80 25.99 25.34 0.499 23.35 27.20 25.75 0.986 24.05 27.60 26.21 0.794
Head length (% body depth) 102.23 102.23 132.63 121.08 10.537 127.58 186.49 153.40 11.409 111.64 156.60 137.16 11.096
Head depth at nape (% SL)* 17.21 14.90 17.21 16.10 0.791 13.06 15.84 14.38 0.734 14.60 16.57 15.79 0.531
Head depth at nape (% HL) 66.22 59.30 68.70 64.48 3.209 52.81 59.43 55.82 1.971 57.09 64.32 60.27 1.975
Barbel length (% HL) 34.29 34.29 47.90 41.41 5.128 26.90 50.00 39.45 5.569 25.42 40.21 31.97 4.092
Maximum head width (% SL)** 15.42 14.61 16.20 15.38 0.653 13.13 15.19 13.83 0.547 12.90 15.77 14.70 0.767
Maximum head width (% HL) 59.33 58.20 64.00 61.25 2.719 50.03 56.98 53.64 2.192 49.83 59.08 55.98 2.024
Snout length (% SL)**** 11.33 8.40 11.33 9.75 0.997 8.94 11.98 10.57 0.625 9.07 11.74 10.16 0.696
Snout length (% HL) 43.59 36.00 43.60 39.40 2.654 37.86 46.38 41.04 2.337 35.93 42.79 38.75 1.903
Eye horizontal diameter (% SL)** 5.24 5.20 5.94 5.49 0.285 5.78 8.15 6.63 0.642 6.36 8.28 7.48 0.463
Eye horizontal diameter (% HL)*** 20.17 20.17 23.97 22.06 1.301 22.72 29.97 26.25 1.809 24.69 32.29 28.54 1.874
Eye horizontal diameter (% interorbital width)** 58.73 58.73 67.50 63.35 4.101 75.25 130.37 103.18 14.774 86.33 121.43 103.22 7.479
Postorbital distance (% HL)**** 44.15 43.20 48.76 45.89 2.111 37.27 48.97 42.38 2.756 37.93 45.81 41.91 2.408
Interorbital width (% SL)* 8.93 8.15 8.93 8.56 0.375 5.23 8.33 6.56 0.811 6.74 7.96 7.26 0.368
Interorbital width (% HL)** 34.34 32.48 35.78 34.25 1.316 19.46 31.26 25.45 2.970 25.12 30.25 27.70 1.384
Number of predorsal vertebrae**** 11 10.00 11.00 10.67 0.516 10.00 11.00 10.50 0.510 10.00 11.00 10.82 0.395
Number of abdominal vertebrae*** 19 19.00 19.00 19.00 0.000 18.00 21.00 19.42 0.703 20.00 21.00 20.18 0.395
Number of caudal vertebrae 21 20.00 21.00 20.83 0.408 19.00 21.00 20.00 0.632 19.00 21.00 19.91 0.610
Number of preanal caudal vertebrae 4 3.00 4.00 3.50 0.548 2.00 3.00 2.58 0.504 2.00 3.00 2.45 0.510
Total vertebrae**** 40 39.00 40.00 39.83 0.408 38.00 41.00 39.42 0.809 39.00 41.00 40.09 0.610
Difference between abdominal and caudal numbers*** -2 -2.00 -1.00 -1.83 0.408 -2.00 2.00 -0.58 1.065 -1.00 2.00 0.27 0.827
Dorsal-fin branched rays (without ½)*** 8 8.00 8.00 8.00 0.000 8.00 8.00 8.00 0.000 7.00 7.00 7.00 0.000
Scales in lateral row 44 41.00 44.00 42.67 1.033 40.00 42.00 41.08 0.744 39.00 43.00 41.14 1.037
Lateral-line scales (total)*** 43 41.00 43.00 42.00 0.894 39.00 42.00 40.73 1.002 39.00 43.00 41.00 1.024
Lateral-line scales (to posterior margin of hypurals)*** 42 39.00 42.00 40.33 1.366 38.00 40.00 38.88 0.766 37.00 40.00 38.77 0.869
Scales above lateral line* 6 6.00 6.00 6.00 0.000 4.00 5.00 4.96 0.196 5.00 6.00 5.59 0.503
Scales below lateral line* 4 4.00 4.00 4.00 0.000 3.00 3.00 3.00 0.000 3.00 4.00 3.32 0.477

Note on syntypes of R. antipai

As already clarified (Kottelat 1997), the species group name antipai is based on 13 syntypes (Bănărescu 1953: 300) without any catalogue numbers. Soon after, Bănărescu (1961: 344) designated a holotype (“Mus. Gr. Antipa Bukarest, Col. Ichth. Nr. 4) but this action is not valid (Art. 74.5 of the International Code of Zoological Nomenclature; International Commission on Zoological Nomenclature 1999). The referred article of the Code says that a subsequent use of the term “holotype” does not constitute a valid lectotype designation unless (italics ours) the author, when wrongly using that term, explicitly indicated that he or she was selecting from the type series that particular specimen to serve as the name-bearing type. We do not know a publication by Petru Bănărescu where he used the term holotype for that specimen explicitly indicating its name-bearing role. However, it cannot be excluded that a valid lectotype designation has been already undertaken by someone because the ANSP syntype is labelled as a paralectotype.

Comparisons

The three examined samples of Romanogobio kesslerii s.l. demonstrate a statistically significant difference in ten morphometric and five meristic characters (Table 3) but the ranges of character values overlap considerably and the number of specimens is small. We combined all specimens in a single sample in order to estimate general ranges of character values without a special analysis of variation within the R. kesslerii complex.

Measurements and counts for examined specimens of Romanogobio kesslerii species complex. * refers to characters demonstrating statistically significant differences (Kruskal-Wallis test, p<0.01).

Characters R. kesslerii Danube n=10 R. kesslerii Romania n=6 R. kesslerii Bulgaria n=10
min max Mean SD min max Mean SD min max Mean SD
SL, mm 50.10 63.42 59.06 3.952 45.11 74.69 57.37 10.157 55.06 66.51 61.31 3.584
Body depth at dorsal-fin origin (% SL) 15.59 17.93 16.81 0.916 16.54 18.30 17.39 0.649 15.73 18.63 16.65 0.787
Depth of caudal peduncle (% SL)* 7.08 7.67 7.37 0.195 6.79 7.34 7.04 0.211 6.33 7.08 6.70 0.214
Depth of caudal peduncle (% length of caudal peduncle) 24.90 33.24 28.84 3.215 28.24 32.85 31.17 1.629 27.17 33.44 31.05 1.865
Predorsal length (% SL) 46.10 48.81 47.39 0.874 44.23 46.70 45.90 0.934 43.41 49.32 46.56 1.826
Postdorsal length (% SL)* 44.25 47.49 45.58 1.260 41.26 44.25 43.27 1.133 39.56 44.64 42.63 1.537
Prepelvic length (% SL) 46.33 49.78 47.84 1.324 46.27 48.69 47.32 0.976 44.79 49.33 47.15 1.250
Preanal length (% SL) 67.12 73.01 70.44 2.227 68.81 71.04 69.90 0.842 67.14 71.01 69.39 1.274
Pectoral – pelvic-fin origin length (% SL) 22.95 23.89 23.27 0.335 23.18 25.18 23.92 0.705 21.15 25.42 23.51 1.230
Pelvic – anal-fin origin length (% SL) 18.66 22.29 21.06 1.307 20.72 22.16 21.34 0.467 18.91 24.84 22.16 1.644
Caudal peduncle length (% SL)* 24.49 29.11 26.35 1.642 21.15 24.14 23.18 1.139 20.21 23.70 21.62 1.099
Pectoral-fin length (% SL)* 22.82 24.00 23.24 0.362 20.43 23.99 22.47 1.167 19.69 23.09 21.01 1.063
Pelvic-fin length (% SL) 17.69 19.10 18.36 0.451 17.19 18.71 18.09 0.508 16.13 18.74 17.44 0.832
Head length (% SL) 25.54 27.20 26.40 0.458 23.35 26.66 25.47 1.181 24.25 26.86 25.28 0.977
Head length (% body depth) 144.23 186.49 158.35 12.847 127.58 159.58 147.35 11.663 139.47 170.77 152.09 8.209
Head depth at nape (% SL)* 13.97 15.84 14.91 0.697 13.83 14.97 14.49 0.410 13.06 14.56 13.79 0.454
Head depth at nape (% HL) 53.04 59.43 56.36 2.349 54.72 59.23 57.01 1.428 52.81 56.20 54.56 1.058
Barbel length (% HL) 32.95 47.64 39.49 5.449 37.63 50.00 43.50 4.540 26.90 43.61 36.99 5.233
Maximum head width (% SL) 13.18 14.30 13.61 0.404 13.13 15.19 14.08 0.657 13.21 14.73 13.91 0.571
Maximum head width (% HL)* 50.03 52.57 51.25 0.976 53.24 56.98 55.35 1.504 53.15 56.43 55.01 0.861
Snout length (% SL)* 10.37 11.20 10.69 0.264 8.94 10.41 9.85 0.534 10.21 11.98 10.89 0.616
Snout length (% HL)* 39.37 42.13 40.40 0.869 37.86 39.61 38.66 0.687 38.32 46.38 43.12 2.260
Eye horizontal diameter (% SL) 6.20 8.15 7.03 0.772 5.78 7.26 6.47 0.570 5.92 6.77 6.31 0.244
Eye horizontal diameter (% HL) 25.14 29.97 27.47 1.896 25.31 27.57 26.29 0.802 22.72 27.36 25.00 1.321
Eye horizontal diameter (% interorbital width) 78.47 130.37 103.10 18.289 75.25 112.80 93.59 14.198 97.90 122.36 109.01 7.799
Postorbital distance (% HL) 39.71 48.97 43.11 3.323 42.00 45.47 43.86 1.350 37.27 43.56 40.75 2.001
Interorbital width (% SL)* 6.04 7.90 7.00 0.635 6.39 8.33 7.06 0.709 5.23 6.24 5.81 0.367
Interorbital width (% HL)* 22.93 30.92 26.52 2.674 25.06 31.26 27.71 2.241 19.46 25.43 23.03 1.827
Number of predorsal vertebrae* 10 11 10.80 0.422 10 11 10.83 0.408 10 10 10.00 0.000
Number of abdominal vertebrae* 19 21 20.00 0.471 19 20 19.50 0.548 18 19 18.80 0.422
Number of caudal vertebrae 19 21 19.90 0.738 20 21 20.50 0.548 19 20 19.80 0.422
Number of preanal caudal vertebrae 2 3 2.30 0.483 2 3 2.67 0.516 2 3 2.80 0.422
Total vertebrae* 39 41 39.90 0.568 40 40 40.00 0.000 38 39 38.60 0.516
Difference between abdominal and caudal numbers -2 2 0.10 1.101 -2 0 -1.00 1.095 -2 0 -1.00 0.667
Dorsal-fin branched rays (without ½) 8 8 8.00 0.000 8 8 8.00 0.000 8 8 8.00 0.000
Scales in lateral row* 41 42 41.50 0.527 41 42 41.33 0.516 40 42 40.50 0.707
Lateral-line scales (total) 40 42 41.10 0.994 40 42 41.00 0.894 39 42 40.20 0.919
Lateral-line scales (to posterior margin of hypurals)* 39 40 39.50 0.527 38 40 38.67 0.816 38 39 38.40 0.516
Scales above lateral line 4 5 4.90 0.316 5.0 5 5.00 5.0 5 5 5.00 0.000
Scales below lateral line 3 3 3.00 0.000 3.0 3 3.00 3.0 3 3 3.00 0.000

As can be seen from Table 2, examined specimens of R. antipai including the NMNHS specimen from the Danube at Vetren, most clearly (with a gap or ranges only slightly overlapping) differ from both R. kesslerii and R. vladykovi by the caudal peduncle depth (35–38.5% caudal peduncle length vs 25–33 and 39–50, respectively), a wider head (58–64% HL vs 50–59), a smaller eye (5–6% SL and 59–67.5% interorbital width vs 6–8 and 75–130), and a wider interorbital space (32.5–36% HL vs 19.5–31; 8–9% SL vs 5–8) with shallow orbital notches (Fig. 2a–c). Romanogobio antipai can be further distinguished from R. kesslerii, besides the number of scales above and below the lateral line (6 and 4, respectively, in all examined R. antipai vs commonly 5 and 3 in R. kesslerii s.l.), by a deeper body (19–25% SL vs 16–19), a deeper caudal peduncle (8–9% SL vs 6–8), and a deeper head (59–69% HL vs 53–59).

Besides morphometric characters mentioned above, all examined specimens of R. antipai including the NMNHS specimen can be clearly distinguished from R. vladykovi by the number of branched dorsal-fin rays, 8½, in contrast to 7½ found in all specimens of R. vladykovi examined in this study. Naseka (2001: 111) mentioned that 8½ rays can be rarely found in R. vladykovi; a revision of his primary data (radiographs) revealed a single specimen with 8½ branched dorsal-fin rays out of 46 examined. Romanogobio antipai further differs from R. vladykovi by the vertebral structure (Table 1, 2) having abdominal+caudal counts 19+21 or 20+21, which means that the caudal region is longer than the abdominal region vs. commonly (in 52 out of 70 specimens) 20+20 or 21+21 or variants with a caudal region shorter than the abdominal one.

A DFA (Fig. 3) showed differentiation of the three groups of samples identified as R. antipai, R. kesslerii and R. vladykovi (the number of unbranched dorsal-fin rays was excluded from the analysis as demonstrating zero variability within the groups) and the groups were 100% classified as predicted (Table 4). A CA (Fig. 4) supported the grouping.

Results of DFA classification for three groups of samples (R. antipai, R. kesslerii and R. vladykovi).

Group Classification matrix (Romanogobio 3 species)
Rows: Observed classifications
Columns: Predicted classifications
Percent correct R. antipai R. kesslerii R. vladykovii
R. antipai 100.0 6 0 0
R. kesslerii 100.0 0 26 0
R. vladykovii 100.0 0 0 22
Total 100.0 6 26 22
Figure 3. 

DFA (Euclidean distance, complete linkage clustering algorithm), distribution of discriminant scores along two canonical discriminant functions established to discriminate between three groups of samples (R. antipai, R. kesslerii and R. vladykovi). Solid circle corresponds to NMNHS specimen identified as Romanogobio antipai.

Figure 4. 

CA (SPSS, k-means) for three groups of samples (R. antipai, R. kesslerii and R. vladykovi). No 1 refers to NMNHS specimen identified as Romanogobio antipai.

To conclude, the analysis confirmed previously reported discriminating character states (number of branched dorsal-fin rays, relative size of the eye and the interorbital space, relative depth of the caudal peduncle) and introduces a new character (vertebral counts) for discriminating Romanogobio antipai from R. kesslerii and R. vladykovi. However, relative taxonomic status of these three species still waits for a phylogenetic analysis based on molecular data. It cannot be excluded that R. antipai is a deep-water ecophenotype of either R. kesslerii or R. vladykovi. The new record demonstrates that R. antipai is still extant in the lower Danube but at present can only be found at a greater depth in the main channel and the deltaic branches. Currently classified as Extinct using IUCN criteria, the conservation status of Romanogobio antipai needs revision, in light of the new record from 2016.

Acknowledgements

NGB was supported by Lise Meitner Programme of National Science Foundation of Austria (M 2183-B25). Our sincere thanks go to Ernst Mikschi and all other members of the NMW Fish Collection, and Melanya Stan and Alexandru Iftime (MGAB), for their valuable help in studying the collections under their care; Mark Sabaj Pérez and Kyle Luckenbill (ANSP) for sending photos and a radiograph of a R. antipai syntype; and to Alice Schumacher (NMW) for making photos of NMW specimens.

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