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Home , Eudontomyzon, European river lamprey, Iskar (river), Lampetra, Lethenteron, Sea lamprey

Folia Zool. – 56(2): 213–224 (2007)

The lampreys of

Tihomir STEFANOV1, 2 and Juraj HOLČÍK1,*

1 Institute of Zoology, Slovak Academy of Sciences, Dúbravská cesta 9, 845 02 , Slovak Republic; *Present address: Drotárska cesta 19, 811 02 Bratislava, Slovak Republic; e-mail: [email protected] 2 National Museum of Natural History, Bulgarian Academy of Sciences, 1 Tzar Osvoboditel Blv., 1000 , Bulgaria; e-mail: [email protected]

Received 17 January 2007; Accepted 4 June 2007

A b s t r a c t . The collections of the National Museum of Natural History – Sofia and the Regional History Museum – Ruse were examined in order to determine the species composition of the family Petromyzontidae in Bulgaria. In contrast to the four species of lampreys reported in the scientific literature as being present in Bulgaria, i.e. fluviatilis, L. planeri, danfordi, and E. mariae, only the latter species was determined in the Bulgarian material. The distribution of this species in Bulgaria is restricted to the River basin. The occurrence of E. hellenicus in the Bulgarian segment of the Struma River basin is anticipated in all probability. The species composition of lampreys inhabiting the streams emptying directly into the remains to be investigated.

Key words: Petromyzontidae, Eudontomyzon mariae, geographic distribution, Danube River basin, Bulgaria

Introduction

There are serious gaps in the knowledge of the geographical distribution and the species composition of lampreys in the system of the Danube River and especially in the right tributaries of the Middle and Lower Danube (H o l č í k 1995). Concerning the Bulgarian segment of the Lower Danube, a total of four species of lampreys are reported to occur in Bulgaria according to the ichthyological literature. These are the European – Lampetra planeri (Bloch, 1784), the – L. fluviatilis (Linnaeus, 1758), the Carpathian lamprey – Eudontomyzon danfordi Regan, 1911, and the – E. mariae (Berg, 1931). K o v a č e v (1923)1 was the first who to publish data on lamprey species from Bulgarian fresh waters. He mentioned two species – Lampetra planeri [as Petromyzon planeri, p. 136] and L. fluviatilis [as P. fluviatilis, p. 136]. Later, M o r o v (1931) in his monograph about the freshwater of Bulgaria simply repeated these two species with the same description and distribution as K o v a č e v . D r e n s k i (1935) studied the lampreys from Danube River and listed two other species for Bulgaria – Eudontomyzon danfordi [as Lampetra danfordi, p. 105] and E. mariae [as L. mariae, p. 106]. D r e n s k i (1948) added L. planeri to the previous two species for the Bulgarian sector of Danube River, but later, he listed only L. planeri and E. danfordi (D r e n s k y 1951). These two species are mentioned also in the paper by M a r i n o v (1978) on the fauna of the Bulgarian segment of the Danube River but with doubts as to their correct identification. The Bulgarian Red Book (B o t e v & P e š e v 1985) listed these species L. planeri and E. danfordi as extirpated and this statement is repeated in the monograph of K a r a p e t k o v a & Ž i v k o v (1995) on the fishes in Bulgaria. However, the list of Bulgarian lampreys published by Ž i v k o v et al. (2005) indicates two species, the Carpathian lamprey, E. danfordi, and the Ukrainian

1 Transliteration of the Bulgarian as well as the Russian Cyrillic alphabet follows ISO No. 9 (1955).

213 lamprey, E. mariae. Additionally, V a s s i l e v & P e h l i v a n o v (2005) presented again E. danfordi in both the Danube River and its tributaries , , Osăm and the Rusenski Lom, as well as L. planeri occurring in the Danube, Iskar and Jantra rivers. However, it needs to be emphasized that all data of these Bulgarian authors are not supported by the analysis of specimens caught in the Bulgarian water bodies. The only lamprey specimens caught in the Bulgarian streams, and investigated and published in the Bulgarian ichthyological literature are from the 60ies of the past century. First K o l a r o v (1960) published the finding of one ammocoete in the Danube River near the town of Lom (Danube river km 747). He determined it to be a Carpathian lamprey, E. danfordi, but he was not sure, since he only had an ammocoete available. Later U n d ž i j a n (1964) found two adult specimens in the Danube River, near Ruse (r. km 494) and again determined them as E. danfordi. It seems that this determination by both authors had been influenced by the statement of B e r g (1948) that E. danfordi “Occurs in the whole Danube River basin” and “Probably it occurs in the Danube proper” (B e r g 1948, p. 32). This claim by Berg has been repeated by V l a d y k o v & K o t t (1979) who wrote (p. 11) that E. danfordi is distributed “throughout the Danube River system, but principally in the River Tisa ()… ”. It is evident that although lampreys have been known from Bulgaria for a long time, their specific identity is still in doubt. The incorrect identification of adults, and especially of larvae, has resulted in conflicting conclusions. Now, it is well known that the range of E. danfordi is restricted to the Tisza and Timiş rivers (B ă n ă r e s c u 1969, R e n a u d & H o l č í k 1986) and that the distribution of L. planeri and L. fluviatilis is far from Bulgaria (H a r d i s t y 1986a,b). The purpose of this paper is to clarify the species composition and the present status of lampreys in Bulgaria based on the analysis of the lamprey samples examined from Bulgarian institutes.

Material and Methods

All the lamprey material collected from Bulgaria and deposited in the National Museum of Natural History – Sofia (NMNHS; institutional code follows K o t t e l a t 1997) as well as in the Regional History Museum – Ruse (RHM-R) has been examined. A total of 11 adults and 5 ammocoetes collected in Bulgarian waters have been investigated (Fig.1, the numbers on the map refer to those in the following text). Adults. 1) RHM-R 558: Danube River, near Ruse, 27.03.1962, 1 male, Tl (total length) 141.9 mm (determined as E. danfordi by E. Undžijan); RHM-R 557: Danube River, near Ruse, 28.03.1962, 1 female, Tl 144.4 mm (determined as E. danfordi by E. Undžijan); 2) NMNHS 327/3: Osăm River, near Levski Railway station, 25.10.1930, 1 male, Tl 142.7 mm (determined as E. mariae by P. Drenski); 3) NMNHS 326/11: Osăm River, near Kolejca village, 23.02.1930, 1 female, Tl 135.8 mm (determined as E. mariae by P. Drenski); 4) NMNHS 326/4: Vit River, near Somovit, 30.03.1930, 1 male, Tl 178.9 mm (determined as E. danfordi by P. Drenski); 5) NMNHS 327/1: Vit River, near , 30.03.1930, 1 female, Tl 190.5 mm (determined as E. mariae by P. Drenski); NMNHS 327/2: Vit River, near Pleven, 30.03.1930, 1 female, Tl 184.4 mm (determined as E. mariae by P. Drenski); 6) NMNHS 326/3: River, District, 25.03.1938, 1 female, Tl 180.1 mm (determined as E. danfordi by P. Drenski); 11) NMNHS 326/7: Rusenski Lom River near Ruse, 1 female, Tl 156.7 mm, NMNHS 326/9: Rusenski Lom River near Ruse, 1 male, Tl 132.3 mm; NMNHS 326/10: Rusenski Lom River near Ruse, 1 female, Tl 138.6 mm (all caught on 24.10.1929 and determined as E. danfordi by P. Drenski).

214 Fig. 1. Map of distribution of lampreys in Bulgaria, according to the literature (○; exact locations are not known) and samples from the museum collections investigated (●).

Ammocoetes. 7) RHM-R 556: Danube River, near Lom, 13.06.1959, Tl 158.9 mm (determined as E. danfordi by E. Undžijan); 8) NMNHS 326/12: Osăm River, near Levski Railway station, 25.10.1930, Tl 141.1 and 126.7 mm; 9) NMNHS 326/8: Rusenski Lom River, near Ruse, 24.10.1929, Tl 126.1 mm; 10) NMNHS (uncatalogued): Danube River, near Ruse, October 2005, Tl 165.6 mm.

Fig. 2. A. Evaluated pigmentation areas of ammocoete (according to R e n a u d 1982): 1 – upper lip, 2 – between upper lip and cheek, 3 – cheek, 4 – subocular, 5 – upper prebranchial, 6 – lower prebranchial, 7 – upper branchial, 8 – lower branchial. B. Tongue precursor showing 1 - the bulb and 2 - the elastic ridge (after V l a d y k o v et al. 1975).

215 The counts (oral disc dentition, trunk myomeres) and measurements were made according to the scheme developed by V l a d y k o v & F o l l e t t (1958) and generally adopted by recent authors (H o l č í k 1986a). Terminology of the disc teeth and velar tentacles follows Vladykov & Follett (1967) and Vladykov & Kott (1976), respectively. Measurements were made on the left side of the specimens and were taken with mechanical calipers to 0.1 mm. Acronyms for counts and measurements used in tables are as follows: Tl – total length; TM – number of trunk myomeres; SO – number of cusps in supraoral lamina; IO – number of cusps in infraoral lamina; AC – number of teeth rows in anterior disc field

(anterials); AC1 – number of teeth in first row of anterior disc field; PC – number of teeth rows in posterior disc field (posterials); PC1 – number of teeth in first row of posterior disc field; Ex – number of exolateral teeth rows (exolaterals); En – number of endolateral teeth (endolaterals); TL – number of cusps in transverse lingual lamina; VT – number of velar tentacles; d-B1 – prebranchial length; B1-B7 – branchial length; B7-a – trunk length; a-C – tail length; d – disc length; d-O – preocular length; O – eye length (horizontal diameter of eye); hD2 – second dorsal fin maximum depth; UGP – length of the urogenital papilla; Int – intestine diameter. The pigment coverage of both the particular parts of body and the tongue precursor of ammocoetes (Fig. 2) was evaluated according to the method used by R e n a u d (1982): 0 = non pigmented, + = 1 – 25 %, ++ = 25 to 75 %, +++ = more than 75 %. For the determination of the different stages of metamorphosis in the ammocoetes, the classification established by B a l a b a i (1958) was used.

Results

M o r p h o l o g y

The morphological characteristics are presented in Tables 1 and 2 for the adults, and 3 for the ammocoetes. Total body length of the adults is between 132.3 and 190.5 mm. Caudal fin of all specimens was spade-like in shape. The number of trunk myomeres in adults varied from 54 – 66 with mean of 62.09. Velar apparatus of the examined specimens had 7 (n=2), 8 (1), 9 (1), 10 (2), 11 (2) and 12 (1) tentacles. Their average number was 9.44 ± 1.81. Median tentacles were usually

Fig. 3. Velar tentacles of E. mariae from Bulgaria (A – Osăm River, ♀, 135.8 mm, 10 velar tentacles, 4 on the left lateral side and 5 (4 are visible) on the right lateral side, 1 long median tentacle; B – Vit River, ♀, 190.5 mm, 12 velar tentacles, 4 on the left lateral side and 6 on the right lateral side, 2 short median tentacles; C – Vit River, ♀, 184.4 mm, 11 velar tentacles, 5 on the left lateral side and 4 on the right lateral side, 2 short median tentacles.

216 3-6) 1-2 - 2 – 3 4 – 9 2 – 5 2 – 5 5 – 9 0 – 3 5 – 11 7 – 12 0 – 17 Ranges 57 – 66 1-2 1-2 2-2 2-2 1-3 1-2 3.6 – 5.4 4.1 – 7.1 1.2 – 2.1 2.7 – 6.5 0.6 – 1.3 0.1 – 0.3 9.8 – 11.9 8.0 – 11.5 49.5 – 53.2 28.8 – 32.2 135.8 - 190.5 (2-5 - -4.17) 9.71 4.18 5.68 1.59 4.39 0.95 0.21 9.17 1.50 2.14 8.00 6.71 9.71 3.71 2.86 1.57 6.60 10.63 50.49 30.05 63.00 161.5 Mean 1.71 1.57 1.86 1.71 2.00 2.00 (3.50- 7 7 7 7 7 7 7 2 6 7 6 6 7 7 7 7 7 7 7 7 5 7 n 7 -3) -2 7 1 2 8 9 0 4 2 0 1 63 9.9 3.6 4.1 1.2 2.7 0.6 0.3 8.0 49.5 32.2 1 1 2 2 2- 156.7 1 1 (3- 24.10.1929 -4) Rusenski Lom ? 0 8 1 2 7 4 8 3 2 2 65 9.8 3.7 5.3 1.4 2.8 0.3 9.4 53.2 29.5 2 1 2 2 1 1 138.6 (3- ) Tl -5) -3 0 1 2 7 7 8 4 3 1 1 57 10 4.1 4.7 2.1 3.8 0.2 8.2 51.0 31.4 10.0 2 2 2 2 2 2 3- 135.8 Osăm (4- Counts 23.02.1930 Measurements (in % of -3) ? 7 2 3 9 6 5 5 2 16 63 4.0 6.6 1.7 4.5 1.3 0.2 11.9 50.1 28.8 10.8 2 2 2 2 2 2 180.1 (2- 25.03.1938 Zlatna Planega -6) -3 0 2 2 9 7 3 4 2 1 1 12 63 4.3 6.1 1.4 6.5 0.1 11.3 49.6 29.0 10.4 2 2 2 2 2 2 3- 190.5 (4- Vit , respectively. 30.03.1930 -4) -4 TL 0 2 2 8 2 3 2 1 11 11 16 66 5.4 7.1 1.5 5.9 0.2 11.5 50.2 29.1 10.7 2 2 2 2 3 2 4- 184.4 (5- -2 - - ? 0 2 5 6 4 3 3 1 64 17 4.3 5.7 1.8 4.6 9.8 10.7 49.7 30.4 2 2 2 2 1 1 2- 144.4 Danube 28.03.1962 Locality and date of capture 7 Counts and measurements of females. Details on velar tentacles in brackets: marginal figures = number of lateral tentacles, bold figures = number of median 1 1 1 2 - a - B D O 7 Ex IO TL En (mm) VT SO 1 AC PC TM hD AC PC UGP a - C d - O B d - B B Tl Int (mm) Character Table 1. Table tentacles and enlarged median cusp in

217 shorter than the neighbouring lateral tentacles. In two lampreys from the Rusenski Lom the median tentacles were as long as the neighbouring lateral tentacles. While the lampreys from the Osăm and the Rusenski Lom rivers possessed only a single median tentacle, all four lampreys caught in the Vit and Zlatna Planega rivers displayed two or three. Some lateralmost tentacles formed wings (Fig. 3), i.e. they were folded onto the dorsal aspect of the velar apparatus. Some of the median and lateral tentacles bore accessory tentacles. The number of right lateral tentacles varied from 3–6 (mean 4.11 ± 0.93), those of the left side from 2–5 (mean 3.78 ± 0.97). All teeth in the oral disc were blunt. The supraoral lamina bore 2 teeth separated by a bridge. In one case (lamprey from the Zlatna Panega River, NMNHS 326/3) supraoral lamina had 3 teeth. Teeth at both ends of this lamina were enlarged and in one specimen (No. coll. 327/2) both were bicuspid. The infraoral lamina bore 5 to 11 teeth. The first row of the anterior disc field contained from 4–9 enlarged teeth. The first row of the posterior field is extremely variable, as it contained from 0–18 teeth of the same size. In two specimens this row is incomplete; its formula was 2–0–2 (i.e. two teeth on both sides) in the male from the Vit River (NMNHS 326/4) and 7–0–1 in the female from the Osăm River (NMNHS 326/11). In another male from the Vit River (NMNHS 327/1) only three teeth were found in the centre of this row, and in one female from the Rusenski Lom River (NMNHS 326/10) eight teeth were visible on one side. The most frequent endolateral formula was 2-2-2 (36.4 %), followed by 1-2-2 (22.7 %); 2-2-1 and 1-2-1 (both 18.2 %) and 2-2-3 (4.5 %). The number of the teeth rows in the anterior field varied from 2–5. Transverse lingual lamina had 5–9 cusps of which the median one was enlarged. Colouration is influenced by the long preservation in formalin and therefore the mottling of ammocoetes, which is a characteristic feature of E. mariae, is not visible. Nevertheless, the dark pigmentation of the tail in both the ammocoetes and adults is visible in most specimens. The tongue precursor of ammocoetes is unpigmented however, in one specimen from the Osăm River its bulb is pigmented on the sides (Table 3). The measurements are very variable (Tabs 1–3) and their comparison is not possible due to different origin, date of capture, and their insufficient number. The sexual dimorphism seems to be the same as in other freshwater lampreys though the long preservation in formalin has distorted the specimens and the different curvature of females and males tail is not clearly expressed. Females had well developed pre- and postcloacal fin-like folds. Urogenital papilla was developed in most males (Table 2) but also in two females (Table 1).

Bionomy and Ecology

The finding of metamorphosed ammocoetes in the Rusenski Lom River and in the Danube River, near Ruse on 24.10.1929 and October 2005, respectively, indicates that metamorphosis in this species occurs in autumn. One female caught in the Vit River near Pleven was post- spawning as its ovaries were empty. According to K o l a r o v (1960) and U n d ž i j a n (1964), the habitat of both metamorphosed lampreys and ammocoetes in the Danube River was a muddy bottom at depths 1.50–1.80 m. This is indirect evidence that E. mariae reproduction was possible also in this segment of the Danube River, where the most part of the bottom is covered by gravel or sand.

218 – 4-4) 1-3 2 – 2 7 – 8 5 – 7 3 – 5 2 – 4 2 – 4 5 – 9 2 2 54-65 9 – 11 4 – 18 1-2 1 Ranges 4.0 – 5.5 5.3 – 6.9 1.3 – 1.4 3.1 – 4.2 0.7 – 1.1 0.2 – 0.2 1-2 1-2 9.6 – 10.8 9.8 – 10.9 48.0 – 50.7 28.5 – 31.5 132.3 – 178.9 (4-5 – -4.00) 1.67 2.00 7.50 6.50 4.00 2.75 2.50 7.00 4.52 6.08 1.38 3.72 0.90 0.20 10.00 12.75 10.22 10.30 49.32 30.25 Mean 60.50 148.95 2.00 2.00 1.75 1.75 50.50 1.00 (4.33- 4 4 3 4 4 4 4 4 4 4 4 3 4 4 4 4 4 4 4 4 3 3 n ) Tl -4) -3 1 2 7 5 4 3 2 1 11 65 10 9.9 4.0 5.7 1.4 3.1 0.7 0.2 10.1 50.0 30.4 1 1 2 2 2 1 3- 132.3 (5- 24.10.1929 Rusenski Lom Counts Measurements (in % of -4) - 9 1 2 7 7 4 2 2 18 61 5.5 6.9 1.4 4.1 0.9 0.2 10.6 50.7 28.5 10.8 1 1 2 2 2 2 142.7 Osăm (4- 25.10.1930 -4) -1 3 2 8 7 4 3 2 2 1 11 62 Vit 9.6 9.8 4.3 5.3 1.3 4.2 1.1 0.2 48.0 31.5 2 1 2 2 1 2 3- 178.9 Locality and date of capture (4- 30.03.1930 -4 - - - 2 8 7 5 4 4 1 18 54 4.3 6.4 1.4 3.5 10.9 48.6 30.6 10.4 2 1 2 2 2 2 4- 141.9 Danube 27.03.1962 7 1 Counts and measurements of the males. 1 1 2 d – a O (mm) – B Ex IO TL En VT 7 SO AC PC TM hD AC PC 1 [mm] UGP a – C d – O d – B B B Tl Int Character

Table 2. Table

219 - 1 2 0 1 – 2 1 – 2 0 – 1 1 – 2 0 – 1 0 – 1 2 – 3 0 – 2 Ranges 62 – 67 4.6 – 7.6 1.0 – 1.1 1.5 – 2.1 10.0 – 12.2 50.8 – 56.7 25.7 – 30.1 126.1 – 165.6 6.57 3.50 1.05 1.74 1.00 1.33 1.33 0.25 1.25 0.50 2.00 0.25 2.75 0.67 0.00 11.18 63.40 54.41 28.54 Mean 143.68 n 5 5 5 5 5 5 1 2 5 3 3 3 4 4 4 4 4 4 3 3 ------D 63 7.3 3.5 1.0 2.1 10.8 56.7 25.7 126.1 24.10.1929 Rusenski Lom ) Tl - - 0 0 0 0 + + + + A 62 ++ ++ ++ 7.6 1.5 11.4 50.8 30.1 126.7 Osăm 25.10.1930 - - 0 0 0 0 + + + A 63 ++ ++ ++ 6.5 1.5 +++ 11.6 52.5 29.1 141.1 Stage of development Counts Pigmentation area Locality and date of capture Measurements (in % of ------F + + + + 67 ++ 4.6 1.1 1.9 +++ 10.0 55.7 28.7 165.6 Oct. 2005 Danube - - 0 0 0 0 0 + + + A 62 ++ ++ 6.9 1.8 +++ 12.2 56.3 29.1 158.9 13.06.1959

7 1 2 1 2 3 4 5 6 7 8 – a O – B [mm] 7 TM hD 1 Bulb a – C d – O d – B B B Tl Character Counts and measurements of the ammocoetes. Caudal fin Elastic ridge

Table 3. Table

220 - 1 2 2 2 1 1 - 1 1 2 2 1 1 - 1 2 2 2 1 - 1 1 2 2 1 - 2 3 2 2 1 - 1 2 1 2 1 - 1 1 2 1 1 Exceptional 2 2 3 1 4.5 - 2 2 1 1 - 2 1 2 1 - 2 1 1 1 - 1 3 1 1 - - - 1 1 - - 1 2 2 - 1 1 2 3 Bulgarian samples Eudontomyzon mariae from all the known and available localities, regardless of the oral disc side (H o l č í k & D e l i ć - - 1 1 2 3 Rare - 1 3 2 3 - 2 3 2 3 - 1 2 2 2 4 Eudontomyzon mariae - 1 2 2 1 6 2 2 1 6 Frequent 18.2 - 1 1 1 6 1 2 2 13 22.7 2 2 2 18 36.4 Common 1 2 1 20 18.2 Comparison of the endolateral formulae of In % in % Group Formula category Frequency Frequency

Table 4. Table 2000) and the Bulgarian samples.

221 Discussion

All of the investigated specimens of lampreys from the Bulgarian ichthyological collections belong to the species Eudontomyzon mariae. This determinaton is confirmed by both their counts and measurements. The numerical values of all characters fitted well into the ranges of E. mariae (Fig. 4). The low number of trunk myomeres in two specimens, 54 in the male from the Danube near Ruse (RHM 558) and 57 in the female from the Osăm River (NMNHS 326/11) is exceptional. In addition, this identification is confirmed by the following qualitative characters: the villiform oral dentition, blunt cusps, exolateral teeth present, thread-like and empty intestine, the spade-like shape of the caudal fin, second dorsal fin without dark blotch, the dark pigmentation of the tail and the unpigmented tongue precursor of ammocoetes. In comparison Lampetra planeri, which is also a non-parasitic species, has weekly developed dentition (posterials and exolaterals absent), of the three enlarged endolaterals, the median is usually tricuspid (in E. mariae bicuspid; tricuspid median tentacle occurs exceptionally – see Table 4), the number of velar tentacles is low (4–7) and wings not occur, pigment is sparse or usually absent on the caudal fin. Concerning the distribution in Bulgaria, there is no doubt that all streams belonging to the Danube River basin, where lampreys were found and/or mentioned by authors in the past, are inhabited by E. mariae. In addition to the Danube River per se, there are the following streams: Lom, Iskar, Vit, Osăm, Jantra, Mindevska reka (tributary of Jantra) and Rusenski Lom. The presence of lampreys in the rivers entering the Black Sea in the area between the Provadijska reka in the north (Varna City region) and the Rezovska reka in the south (border between Bulgaria and ) is not known. It is not excluded that in the

Fig. 4. Comparison of counts and measurements of E. mariae. Generalized data from H o l č í k & D e l i ć (2000).

222 past there occurred the parasitic lamprey similar to that migrating formerly into the Don and Dnieper rivers (K o t t e l a t et al. 2005). Also, it is necessary to find which species of lamprey inhabit the basins of the rivers Marica, Mesta and Struma (Aegean Sea watershed). K o v a č e v (1923) mentioned the capture of one specimen of lamprey (under the name of Lampetra fluviatilis) in the Kričim River, a right-hand tributary of the Marica River. From the Mesta River, the lampreys are not known, but in three brooks of the Greek segment of the Struma (Strymón) River basin, the Greek brook lamprey Eudontomyzon hellenicus Vladykov, Renaud, Kott, and Economidis, 1982 occurs (R e n a u d 1986). Therefore, the occurrence of E. hellenicus in the Bulgarian segment of the Struma River basin is possible. The occurrence of E. mariae in the Lower Danube proves that this species is able to inhabit not only the mountain and foothill zones of watercourses containing clear water with a strong current, but also the slow flowing, large and deep rivers with low transparency. In this respect, this species is similar to kessleri (Anikin, 1905) (H o l č í k 1986b). The distribution of lampreys in Bulgaria may have changed due to the deep human impact in the past caused by deforestation, hydraulic engineering and pollution. Nevertheless, the occurrence of E. mariae in the Lower Danube gives evidence that this species is the most widespread of lampreys in the Danube River basin.

Acknowledgements The authors are indebted to Miloš V a t e r , Jozef Čarnogurský and Ľubomír V i d l i č k a for their assistance in preparing illustrations. The first author is deeply indebted to the Ministry of Education of the Slovak Republic for the scholarship making possible his stay in the Institute of Zoology, Slovak Academy of Sciences in Bratislava. In addition we are grateful to Claude R e n a u d for interest, logistic help, critical comments and linguistic correction and also to two anonymous referees for the helpful comments.

LITERATURE

Balabai P.P. 1958: Metamorfoz minogi [Lamprey metamorphosis]. Izdatel´stvo Akademii Nauk SSSR, Kiev (in Russian). Bănărescu P. 1969: Fauna Republicii Socialiste Romănia. 12/1. şi Chondrichthyes (Ciclostomi şi Selacieni) [Fauna of the Socialistic Republic Rumania. 12/1. Cyclostomata and Chondrichthyes (Cyclostomes and cartilaginous fishes)]. Editura Academiei Republicii Socialiste Romănia, Bucurest (in Rumanian). Berg L.S. 1948: Ryby presnykh vod SSSR i sopredel´nykh stran [Freshwater Fishes of the USSR and adjacent countries]. 1. Izdatel´stvo Akademii Nauk SSSR, Moskva (in Russian). Botev B. & Pešev C. (eds) 1985: Červena kniga na NR Bălgarija. 2. Životni [Red Book of the People’s Republic of Bulgaria. 2. ]. Izdatelstvo na Bălgarskata Akademija na Naukite, Sofia (in Bulgarian). Drensky P. 1935: Petromyzoniden (Pisces) aus dem Donaugebiet. Sitzung Berichte der Gesellschaft Naturforschender Freunde: 102–106. Drenski P. 1948: Săstav i razprostranenie na ribite v Bălgarija [Synopsis and distribution of fishes in Bulgaria]. Godišnik na Sofiiskija universitet, Prirodo-matematički fakultet 3 (Estetstvena Istorija): 11–171 (in Bulgarian). Drenski P. 1951: Fauna na Bălgarija. 2. Ribite v Bălgarija [Fauna of Bulgaria. 2. Fishes of Bulgaria]. Bălgarska Akademija na Naukite, Sofia (in Bulgarian). Hardisty M.W. 1986a: Lampetra fluviatilis (Linnaeus, 1758). In: Holčík J. (ed.), The Freshwater Fishes of Europe. 1/I. Petromyzontiformes. AULA-Verlag, Wiesbaden: 248–278. Hardisty M.W. 1986b: Lampetra planeri (Bloch, 1784). In: Holčík J. (ed.) The Freshwater Fishes of Europe. 1/I. Petromyzontiformes. AULA-Verlag, Wiesbaden: 279–304.

223 Holčík J. (ed.) 1986a: The Freshwater Fishes of Europe. 1/I. Petromyzontiformes. AULA-Verlag, Wiesbaden: 147–164. Holčík J. 1986b: Lethenteron kessleri (Anikin, 1905). In: Holčík J. (ed.), The Freshwater Fishes of Europe. 1/I. Petromyzontiformes. AULA-Verlag, Wiesbaden: 220–236. Holčík J. 1995: Geographic distribution of lampreys (Petromyzontiformes) in the Middle and Lower Danube (between and the Black Sea). Fischökologie 8: 23–30. Holčík J. & Delić A. 2000: New discovery of the Ukrainian brook lamprey in Croatia. J. Fish Biol. 56: 73–86. Karapetkova M. & Živkov M. 1995: Ribite v Bălgarija [Fishes in Bulgaria]. Geya-libris, Sofia (in Bulgarian). Kolarov P. 1960: Edna rjadka nahodka ot reka Dunav [One rare fish finding of the Danube River]. Priroda 3: 70–71 (in Bulgarian). Kottelat M. 1997: European freshwater fishes. Biologia, Bratislava 52 (Supplement 5):1–271. Kottelat M., Bogutskaya N.G. & Freyhof J. 2005: On the migratory Black and the nomenclature of the ludoga, Peipsi and ripus whitefishes (: Petromyzontidae; Teleostei, Coregonidae). Zoosyst. Rossica 14: 181–186. Kovačev V. 1923: Sladkovodnata ihtiologična fauna na Bălgarija [Freshwater ichthyological fauna of Bulgaria]. Arhiv na Minist. Na Zemedelieto i Dărž. Imoti. t.3. Izd. Na Minist. na Zemed., Sofija (in Bulgarian). Marinov B. 1978: Ihtiofaunata na bălgarskija sektor na reka Dunav i nejnoto stopansko značenie (Die Fischfauna im bulgarsichen Donauabschnitt und ihre Bedeutung für die Wirtschaft). In: Rusev B.K. & Naidenov V.T. (eds), Limnologija na bălgarskija sektor na reka Dunav. Izdatelstvo na Bălgarskata Akademija na Naukite, Sofia: 201–228 (in Bulgarian with German summary). Morov T. 1931: Sladkovodnite ribi v Bălgarija [Freshwater fishes of Bulgaria]. Bălgarski Ribarski Săjuz, Sofia (in Bulgarian). Renaud C.B. 1982: Revision of the lamprey Eudontomyzon Regan, 1911. M.Sc. Thesis, University of Ottawa, Ottawa. Renaud C.B. 1986: Eudontomyzon hellenicus Vladykov, Renaud, Kott, and Economidis, 1982. In: Holčík J. (ed.), The Freshwater Fishes of Europe. 1/I. Petromyzontiformes. AULA-Verlag, Wiesbaden: 186–195. Renaud C.B. & Holčík J. 1986: Eudontomyzon danfordi Regan, 1911. In: Holčík J. (ed.), The Freshwater Fishes of Europe. 1/I. Petromyzontiformes. AULA-Verlag, Wiesbaden: 147–164. Undžijan E. 1964: Vărhu edna nahodka na minoga ot reka Dunav (Űber einen Fund von Neunaugen aus der Donau). Izvestija na Narodnija Muzej – Ruse 1: 227–231 (in Bulgarian with German summary). Vassilev M.V. & Pehlivanov L.Z. 2005: Checklist of Bulgarian Freshwater Fishes. Acta Zoologica Bulgarica 57: 161–190. Vladykov V.D. & Follett W.I. 1958: Redescription of (Günther) of western North America, a species of lamprey (Petromyzontidae) distinct from Lampetra fluviatilis of Europe. J. Fish. Res. Bd. Canada 15: 47–77. Vladykov V.D. & Follett W.I. 1967: The teeth of lampreys (Petromyzonidae): their terminology and use in a key to the Holarctic genera. J. Fish. Res. Bd. Canada 24: 1067–1075. Vladykov V.D., Kott E. & Pharand-Coad S. 1975: A new nonparasitic species of lamprey, genus Lethenteron (Petromyzonidae) from eastern tributaries of the Gulf of Mexico, U.S.A. Nat. Mus. Nat. Sci. (Ottawa) Publ. Zool.12: 1–36. Vladykov V.D. & Kott E. 1976: The taxonomic significance of velar tentacles in Holarctic lampreys (Petromyzonidae). Rev. Trav. Inst. Pêches Marit. 40: 787–789. Vladykov V.D. & Kott E. 1979: List of northern hemisphere lampreys (Petromyzonidae) and their distribution. Dept. Fish. Oceans, Ottawa Musc. Spec. Publ. 42: 1–30. Živkov M., Prodanov K., Tričkova T., Rajkova-Petrova G. & Ivanova P. 2005: Ribite v Bălgarija – proučenost, opazvane i ustojčivo izpolzvane (Fishes in Bulgaria: research priorities, conservation and sustainable use). In: Petrova A. (ed.), Current state of Bulgarian biodiversity – problems and perspectives. Bulgarian Bioplatform, Sofia: 247–281 (in Bulgarian with English abstract).

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