J. Great Lakes Res. 27(3):281–289 Internat. Assoc. Great Lakes Res., 2001

Morphology, Feeding, and Reproduction of the Round Goby, melanostomus (Pallas), in the Basin, Yugoslavia

Predrag Simonovic1,*å , Momir Paunovicå2, and Srdja Popovic1å 1Institute of Zoology, Faculty of Biology University of Belgrade Studentski trg 16 11001 Belgrade, Yugoslavia 2Department of Hydrobiology Institute for Biological Research 29 November 142 11000 Belgrade, Yugoslavia

ABSTRACT. The round goby Neogobius melanostomus was the last Ponto-Caspian goby to enter in the Danube River bordered by Serbia and Yugoslavia. There are five Ponto-Caspian goby species in the waters of Serbia including the sand goby Neogobius fluviatilis, the round goby Neogobius melanostomus, the Neogobius gymnotrachelus, the bighead goby Neogobius kessleri, and the tubenose goby marmoratus. The sand, bighead, and tubenose gobies occur along the Yugoslav Danube and in the lower reach of the Danube’s tributaries; the racer goby is found both upstream and downstream of the Djerdap II dam; and, the round goby has been collected only down- stream of the Djerdap II dam. Investigations on the continuous morphological characters of the round goby revealed neither sexual dimorphism, nor significant differences in adult size-classes, although some suggestions of sexual dimorphism were found in cranial skeletal analyses. Analysis of external continu- ous characters revealed a west-east cline along the distribution range of the round goby in the basin. Molluscivory for the round goby was corroborated along the Danube. Standard length of each age class for the round goby in the Danube was less than populations in the Caspian and Azov seas. INDEX WORDS: Round goby, distribution, morphology, feeding, Danube, Yugoslavia.

INTRODUCTION Zweimueller et al. 1996, Simonovicå1996 a, Si- The ichthyofauna of the Danube River basin is monovicå1996b, Erös and Guti 1997, Strañai 1997) well-known, yet new species continue to colo- described the spatial distribution of gobies in the nize the region (Biro 1971, Holc˚ik and Hensel upper and middle Danube sections and in the main 1974, Hegedis˚et al. 1991, Simonovicået al. 1998). tributaries. Recently, Ahnelt et al. (1998) confirmed Banarescu (1964) documented the distribution of that Ponto-Caspian gobies were well established in the Ponto-Caspian gobiids occurring in the waters the upstream areas of the basin. (both inland and marine) of Romania. Smirnov Information on the distribution of Ponto-Caspian (1986) reported the distribution of gobiid species in gobies in Yugoslav section of the Danube from the the lowermost section of the Danube, but mainly literature is scarce and out-of-date (Vukovicåand assigned Vidin (km 790) as the most upstream spot Ivanovicå1971, Risticå1972, Risticå1977). The dis- of their distribution. Others (Biro 1971, Jankovicået covery of the round goby Neogobius (Apollonia al. 1987, Ahnelt 1988, Ahnelt 1989, Ahnelt et al. Iljin 1927) melanostomus (Pallas 1811), as a new 1998, Harka 1990, Hegedis˚et al. 1991, Spindler gobiid species, for the fauna of Serbia and Yu- and Chovanec 1994, Lusk and Halac˚ka 1995, goslavia (Simonovicået al. 1998) completed the knowledge on the distribution of Ponto-Caspian go- bies in the Danube. The recent records on the dis- *Corresponding author: E-mail: [email protected] persal of Ponto-Caspian gobies in the Yugoslav

281 282 Simonovicået al.

FIG. 1. Position of the sampling sites in the Danube drainage in Serbia (Sample sites cor- respond to numbers in Table 1).

stretch of the Danube, and also in the Danube basin, METHODS are of interest because gobiids also are expanding The neogobiids were caught by float and legger their distribution in other regions including in the angling, by using an “umbrella” fishnet (of the size , e.g., Dniepr, Dniestr, (Smirnov 1 × 1 m and mesh size 0.8 × 10–2 m) and by elec- 1986), the River Moscow (Sokolov et al. 1989, trofishing (220 VAC transformed to 220 V DC, 2.1 1994), the (Skora and Stolarski 1993) KW) at sites of the River Danube basin during 1993 and the Laurentian Great Lakes in North America to 1998 (Fig. 1). Sampling locations for the River (Jude et al. 1992). The round and tubenose Pro- terorhinus marmoratus (Pallas 1811) gobies, have Danube basin in Serbia are given in distance from Sulina, i.e., from the mouth into the Black Sea naturally surpassed their original limits of distribu- Î å ˚ tion in the Ponto-Caspian area (Smirnov 1986; onic and Jecinac 1991) (Table 1). Fish were pre- Miller 1986, 1990; Economidis and Miller 1990; served in 70% ethanol and transferred to the labora- Ahnelt et al. 1998). tory for processing. They were identified using The appearance of the round goby as a new taxonomic keys from Banarescu (1964), Smirnov species in the Yugoslav section of the Danube River (1986), and Miller (1986). Most specimens are still is noteworthy. The objective of this study was to stored in the collection of the Institute of Zoology, document the presence of gobiids in the Danube Faculty of Biology, University of Belgrade. River and to determine the relationship between the Using a binocular microscope, age was deter- round goby and other . Also examined were mined on scales taken from the left flank at the the morphology, feeding habits, size of age-classes, level of the first . Fish stomachs were ana- and maturity of the round goby. lyzed and sex and stage of gonad ripeness were Round Goby in the Danube 283

TABLE 1. Authors’ and others data on recent (since 1986) records of gobies in the Danube and its tribu- taries on the territory of Serbia and Yugoslavia: localities, sampling dates, and sizes of both saved and unpreserved samples. Fig. 1 Sampling Date (in ‘d/m/y’, Sample Status in collection Species No. River locality or ‘y’ format) size or source Neogobius melanostomus 1 Danube Prahovo (km 861) 13-15/09/1997 13 + (on loan) Round goby 2 Danube Prahovo (km 861) 01/10/1998 30 + (on loan) Neogobius fluviatilis 3 Danube Zemun (km 1172) 19/09/1993 85 + (in 70% alc.) sand goby 4 Danube Ores˚ac (km 1124) 04/06/1994 3 In 70% alc. 5 Danube Bezdan (km 1426) 13/07/1996 1 — 6 Danube Prahovo (km 861) 15/09/1997 16 + (in 70% alc.) 7 Danube Begec˚(km 1276) ??/??/1986 12 Jankovicået al. 8 Danube Prahovo (km 861) 01/10/1998 10 + (in 70% alc.) 9 Sava Novi Beograd 15/05 1994 16 + (in skeleton) 10 V. Morava Velika Plana 06/09/1998 9 + (in 70% alc.) 11 Sava Sabac (121 km) 24/09/1998 12 + (in 70% alc.) Neogobius gymnotrachelus 12 Danube Prahovo (km 861) 13-15/09/1997 1 + (in 70% alc.) Racer goby 13 Danube Brza Palanka (km 884) ??/10/ 1991 2 + (in 70% alc.) Neogobius kessleri 14 Danube Bezdan (km 1425) 15/10/1996 1 Hegedis˚et al. Bighead goby 15 Danube Prahovo (km 861) 13-15/09/1997 3 + (in 70% alc.) 16 Danube Belgrade (km 1173) 1992 45 + (in 70% alc.) 17 Danube Gradis˚te (km 1062) 29/11/1993 12 — 18 Danube Golubac (km 1042) 30/11/1992 16 + (in 70% alc.) 19 Danube Ores˚ac (km 1124) 04/06/1994 2 + (in 70% alc.) 20 Sava Novi Beograd 1993, 1994 20 + (in skeleton) 21 Sava Sabac (121 km) 09/10/1998 2 + (in 70% alc.) Proterorhinus marmoratus 22 Danube Zemun (km 1172) 1993, 1994 33 + (on loan) Tubenose goby 23 Sava Novi Beograd 24/05/1995 16 + (in skeleton) 24 Tamis˚ Tomas˚evac 21/10/1998 3 + (in 70% alc.) recorded. Non-mollusc food items were identified base length; hA—anal fin height; lP—pectoral fin mainly to order and family levels (Kerovec 1986), length; lV—pelvic disk length). Measures were and molluscs were identified to the and transformed to indices of standard length. Round species levels (Loz˚ek 1956). Items related to spe- goby populations from the Serbian section of the cific aspects of feeding patterns were analyzed by Danube were compared with those from the Azov χ2 Frequency Analysis, with the Yate’s correction and Black seas and the River Dniepr (Smirnov applied (Petz 1985). Correspondence Analysis was 1986). Squared Euclidean distance (Sokal and used to examine overall food partitioning. Rohlf 1981) between means of external continuous Meristic traits of round goby were counted on a characters was used as a measure of (dis)similarity reduced character set (Smirnov 1986) using a dis- between the sample from Prahovo (Fig. 1) and oth- section microscope (× 6). Calipers (0.1 mm), were ers from the literature (Smirnov 1986). The rela- used to measure 15 continuous external morpholog- tionships between analyzed samples were derived ical characters conforming to the character set from the obtained distance matrix using an agglom- given in Holc˚ik (1989) (hmax—maximal body erative UPGMA clustering method (Sokal and height; hmin—minimal body height; aD1—predor- Rohlf 1981). sal length; pD2—postdorsal length; aP—prepec- A multivariate analysis of round goby from the toral length; aV—preventral length; aA—preanal Baltic Sea (the Gulf of Gdansk) was used to exam- length; lD1—first dorsal fin base length; hD1—first ine external morphology (using the truss network dorsal fin height; lD2—second dorsal fin base scheme, i.e., a set of longitudinal, vertical, and di- length; hD2—second dorsal fin height; lA—anal fin agonal distances between homologous points of 284 Simonovicået al. particular body regions; Bookstein et al. 1985), THE ROUND GOBY continuous osteological characters and karyological Morphology characters. These analyses used different techiques, explained in detail in Simonovicåand Nikolicå The values for discrete traits (lateral rows of (1995/1996), Simonovicå(1996a, b, 1999), and Si- scales, number of rays in fins, etc.) given in the lit- monovicået al. (1996). Intraspecific variability of erature (Berg 1949, Svetovidov 1964, Georgiev gobiids was examined to determine phylogenetic 1966, Smirnov 1986) for the round goby were relationships among the five Ponto-Caspian gobiid within the range of values obtained for the round species occurring in Yugoslav waters. goby from the Danube at Prahovo. Although sample sizes for males and females RESULTS AND DISCUSSION were small, analysis on continuous morphometric characters (Table 2) did not reveal sexual dimor- Ponto-Caspian Gobies in Yugoslav Waters phism, corroborating the results derived form the Records were established for the occurrence of multivariate analysis of the “truss box network” sand Neogobius (Apollonia) fluviatilis (Pallas scheme of characters in the round goby from Baltic 1811), bighead Neogobius () kessleri Sea (Simonovicåand Mesaros˚1998). The results of (Günther 1861), and tubenose gobies in the Yu- intraspecific analysis of cranial skeletons in large goslav section of the River Danube. Sand and big- adult round goby (up to 19 cm TL) from the Baltic head gobies occur along the entire Yugoslav section Sea revealed no difference between four size of the River Sava. The occurrences were verified of classes (< 14 cm TL; 14–15 cm TL: 15–16 cm TL; the tubenose goby (upstream from the mouth of the > 16 cm TL), judging from the comparison of their River Tamis˚into the Danube), and the sand goby ontogenetic trajectories (b1 = 0.036 ± 0.243; b2 = (upstream from the mouth of the River Velika –1.241 ± 0.287; b3 = 0.149 ± 0.308; b4 = –0.239 ± Morava into the Danube) (Table 1, Fig. 1). There is 0.144) by q test (q1–2 = 2.438; q2=3 = 2.531; q3–4 unconfirmed information, obtained from anglers, =1.576; k = 4; n = 18; df = 10). These results agree that sand, bighead, and tubenose gobies occur in with the lack of allometric growth in cranial skele- tributaries of the Danube (V. Morava, Sava, Tamis˚) ton elements in large specimens. However, the upstream of the sampling locations (River Tisa in comparison of ontogenetic trajectory of males the vicinity of city Zabalj) (Table 1). The Bentophilus stellatus (Sauvage 1874), has been reported in the one of Djerdap reservoirs (Nal- bant in Ahnelt et al. 1998) and may represent the TABLE 2. Sexual dimorphism of continuous sixth Ponto-Caspian goby species in the Yugoslav characters (in % of standard length) of the round section of the Danube. goby from the Danube at Prahovo (M—mean, In addition to the round goby, three other gobiid SE —standard error of mean; values were not sig- species were caught in the Danube River near the nificantly different). city of Prahovo: sand goby, racer goby Neogobius males (n = 9) females (n = 4) (Babka) gymnotrachelus (Kessler 1857), and big- t(11, 0.05) head goby. According to the catch data from the M SE M SE [2.20] River Danube at Prahovo (Simonovicået al. 1998), Hmax 17.74 1.525 15.43 2.662 0.806 the syntopic gobiid community in the inshore zone Hmin 7.91 0.618 7.00 1.259 0.737 is rather uniform. After repeated sampling in Octo- aD1 27.16 2.150 24.48 3.895 0.652 ber 1998, it was observed that gobiids (sand, big- pD2 13.69 0.849 12.60 1.607 0.660 head, and round goby; the racer goby was not AP 23.77 1.715 21.93 3.300 0.549 caught) share the same littoral habitat with the com- AV 22.51 1.648 20.60 2.858 0.894 AA 44.46 4.013 39.75 6.839 0.626 mon gudgeon Gobio gobio, a small, native, lD1 14.60 1.137 12.98 2.214 0.728 rheophilic, bottom-dwelling cyprinid. The finding hD1 10.89 0.859 10.43 1.667 0.275 of round and tadpole gobies in the lowermost sec- lD2 24.78 1.687 22.58 3.941 0.615 tion of the Danube in Serbia, i.e., downstream from hD2 11.72 0.810 10.40 1.773 0.791 the Îerdap II dam, was expected, since Smirnov LA 18.48 1.459 16.95 2.678 0.545 (1986) documented their occurrence in the Roman- HA 9.33 0.440 8.90 1.154 0.437 ian section of the Danube up to Vidin (km 790), ap- LP 18.79 1.171 17.13 2.293 0.722 proximately 71 km downstream of the Prahovo. LV 16.07 0.972 14.85 2.004 0.623 Round Goby in the Danube 285

TABLE 3. Means(M) and standard errors (SE) of continuous morphological traits of the round goby from the Danube at Prahovo (1), as well as from the River Dniepr (2), Black Sea around the Danube Delta (3), Black Sea in the area of Sevastopolis (4) and Azov Sea in the area of Berdyansk (5), and testing of differences between them (degrees of freedom in brackets; *—p < 0.05; **—p < 0.01). t testing between 1 and: Locality 1 2 3 4 5 2 3 4 5 M SE M SE M SE M SE M SE (38) (53) (36) (60) Hmax 22.40 0.40 24.24 0.52 23.13 0.23 23.61 0.28 25.19 0.20 2.808** 1.584 2.486* .281** Hmin 10.09 0.14 13.10 0.30 10.76 0.10 12.47 0.16 12.72 0.20 9.108** 3.920** 11.239** 10.806** aD1 34.88 0.52 35.44 0.28 34.88 0.23 35.67 0.28 35.27 0.27 0.943 0.009 1.334 0.660 pD2 17.99 0.41 17.77 0.13 15.94 0.16 15.27 0.20 16.11 0.24 0.507 4.635** 5.936** 3.940** AP 30.92 0.35 33.71 0.39 30.04 0.20 33.59 0.21 32.10 0.22 5.310** 2.188* 6.519** 2.839* AV 30.11 0.35 31.88 0.26 30.32 0.20 32.11 0.22 30.80 0.21 4.066** 0.529 4.844** 1.698 AA 56.71 1.16 59.24 0.52 58.78 0.24 59.67 0.39 58.62 0.28 1.988 1.745 2.417* 1.598 lD1 18.64 0.36 19.15 0.37 18.86 0.16 17.99 0.23 18.41 0.15 0.992 0.565 1.502 0.574 hD1 14.33 0.36 17.84 0.16 15.69 0.16 15.83 0.22 16.40 0.20 9.012** 3.495** 3.593** 5.081** lD2 31.96 0.40 33.61 0.36 33.83 0.19 34.03 0.34 33.53 0.21 3.052** 4.193** 3.924** 3.452** hD2 15.08 0.24 15.40 0.22 16.17 0.18 16.35 0.21 16.61 0.21 0.965 3.594** 3.945** 4.754** LA 23.83 0.42 26.74 0.40 26.22 0.20 27.19 0.29 25.48 0.33 5.005** 5.116** 6.558** 3.083** HA 12.51 0.43 14.34 0.29 13.67 0.18 13.03 0.21 15.00 0.24 3.542** 2.500* 1.089 5.081** LP 24.53 0.40 25.90 0.27 26.35 0.16 23.99 0.26 28.78 0.24 2.828** 4.212** 1.142 9.098** LV 21.10 0.41 21.50 0.27 20.16 0.19 18.95 0.40 22.38 0.29 0.820 2.094* 3.769** 2.563*

(bm = –0.108 ± 0.068) with that of females (bf = hovo differs from all others in minimal body height 0.090 ± 0.052) for cranial skeleton characters was (hmin), prepectoral distance (aP), first dorsal fin close to significance for sexual dimorphism (qm-f = height (hD1), second dorsal fin base length (lD2), 3.207; k=2; n=18; df-14; p ª 0.05). The slight sexual and anal fin base length (lA) (Table 3). The similar- dimorphism, both on the Principal Component ity between the Prahovo and Danube Delta Region Analysis loadings (regardless of size-component), samples in a few characters (hmax, aV, aA) may be and on the ANOVA tests, was due mainly to signifi- due to the general stability of those traits. The sam- cant differences for articular plate (p < 0.01) in the ple from the Prahovo is closer to the sample from lower jaw, premaxillar height (p < 0.02) in the the Danube Delta Region for most of characters for upper jaw and supracleithrum—postemporal bridge which a statistical difference was found, implying (p < 0.01) in the pectoral girdle (Simonovicå1996c). some sort of clinal variability for these continuous Comparison of 15 characters (Smirnov 1986) be- traits (aP, hD1, lD2, hD2, lA, and hA). Cluster tween the round goby from the River Danube at analysis (Fig. 2) illustrated the assumption, but it Prahovo and those from the localities at the River needs to be tested. Dniepr, Danube Delta, Sevastopolis region (all from the Black Sea basin), and at Berdyansk (from Feeding the Azov Sea) revealed statistically significant dif- In late summer, the round goby fed mainly on ferences (Table 3). Round gobies in riverine habi- mollusks, especially polymorpha (Dreis- tats have retained similar proportions of predorsal senidae) and followed by Pisidium (Spheriidae) and (aD1), postdorsal (pD2), and preanal (aA) distances Anodonta sp. (Unionidae), the last. Other prey in- and first dorsal fin base (lD1) and ventral disk (lV) cluded two species of snails, Lymnaea peregra and length (Table 3). Few of these characters seem to be Theodoxus danubialis, an amphipod (Gammarus stable in the samples compared, e.g., aD1, aA, and sp.), one Oligochaeta and three insects (Diptera lD1. The remaining characters revealed great vari- and Plecoptera). Gammarids dominated the non- ability, corroborating the findings of Smirnov mollusk prey items. Apparently, the round goby se- (1986), who found differences between his samples lects mollusks and gammarids. Mollusks were the for various continuous traits. The sample from Pra- favored prey item over the non-mollusks in all age- 286 Simonovicået al.

lished data). Unlike the round goby, other gobiids fed on larvae of different insect groups (Chironomi- dae, non-chironomid Diptera, Trichoptera, Ephemeroptera, Hemiptera, Coleoptera, and Odonata), Oligochaeta, goby fry and insect eggs (Fig. 3) in all seasons (sand goby χ2 = 1.76; df = 7; bighead goby χ2 = 6.44; df = 14). However, a clear distinction among goby species based on their diet did not occur (χ2 = 296.74; df = 1560) because bi- valves and gammarids were found in all fishes. On the pairwise testing between species, the significant partitioning for prey occurred among the round goby and sand (χ2 = 14.33, df = 7, p < 0.05) and tubenose (χ2 = 13.19, df = 7, p < 0.1) gobies. A FIG. 2. Phenetic relatioships between round similarity in diets between round and bighead gob- goby samples derived from the UPGMA clustering ies (χ2 = 5.86, df = 7) was attributed to the presence of the Squared Euclidean distances. of gammarids. The similarity in feeding found be- tween all other gobies (χ2 ranging from 3.19 to 10.93, df = 7) was mainly due to their mutual feed- ing on larvae of different insect groups (among classes. The selectivity for mussels over the snails which chironomids dominated), gammarids, and did not occur in age- and size-classes (Simonovicået Oligochaeta. al. 1998). The molluscivory of the Danubian round goby confirmed the findings of Svetovidov (1964). Reproduction Also, Smirnov (1986) concluded that “in general, the diet of the round goby in different regions is In late September 1998, the gonads of male and consisted mainly on mollusks;” Ray and Corkum female round goby were tiny, and firmly attached (1997) stated that zebra mussels Dreissena poly- on the dorsal wall of the body cavity, corresponding morpha were the dominant prey of large (> 7 cm) to II stage of maturity (Moiseev et al. 1981). The round gobies. stage II develoment of gonads in early fall is in The diet of round goby from the River Danube at agreement with the reports of Kulikova and Fan- Prahovo is similar to those reported from other lo- deeva (1975) and Moiseeva and Rudenko (1978), calities with some differences in the taxa of particu- who reported that II and III stages overwinter. In lar food items in round goby samples from marine the other regions, the round goby spawns repeatedly or oligohaline environments. In comparison to the from the end of April to the end of August (Vino- reports dealing with the riverine round gobies, the gradov 1948; Il’in 1949). Spawning episodes per molluscan taxa, specific to the Pontic region (Dreis- year vary from 2 (Trifonov 1955, Kostyuchenko sena polymorpha, Pisidium), were the same as the 1960), 3 to 4 and 4 (Bil’ko 1968, Kalinina 1976), to diet of the round goby in the Danube. 5 to 6 (Kulikova and Fandeeva 1975). Neither fe- cundity, nor the extent of the spawning season of round goby in the middle Danube River is known. Food Partitioning Among Gobies Apart from the extensive data on prey items of Size-at-age neogobiids (Smirnov 1986), other studies have not examined partitioning of prey items among species The standard length of round goby from the Pra- that share the same habitat. Knowledge on the uti- hovo is up to 42 mm (year 0), 77 mm (year 1), and lization of food resources by neogobiids would be 93 mm (year 2). These size-at-age values are some- useful for predicting the outcome of the recently in- what less than those reported from the Azov, Black, troduced round goby in the Yugoslav section of the and Caspian seas (Fig. 4). According to Berg Danube. On the basis of the neogobiid samples (1949), the round goby achieves 45 (n=105) from several localities (1, 3, 4, 9, 11, 16, mm and 95 mm in age-classes 0 and 1, respectively, 18, 19, 24, and 21; Table 1), the round goby may and the Azov Sea values are 70 mm, 120 mm, and feed in the nearshore areas of the Danube (unpub- 140 mm in age classes 0, 1, and 2, respectively. Ac- Round Goby in the Danube 287

FIG. 3. UPGMA clustered correspondent scores on Euclidean distances (small insert) between goby species from the Yugoslav section of the Danube and its tributaries, presenting feeding pattern, with its most prominent determinants from the Correspondence Analysis applied.

FIG. 4. Growth-in-length (SL) of round goby from Danube, Prahovo compared with those from Azov and Caspian Seas (taken from the literature; see text). 288 Simonovicået al. cording to Smirnov (1986), the Azov Sea round Îonicå, M., and Jec˚inac, R. 1991. Dunav od Bezdana do goby grows up to 50 mm, 99 mm, 116 mm, and 123 Timoka [Danube from Bezdan to Timok]. Belgrade: mm in age classes 0 to 3, respectively. Pronalazas˚vo. Small intraspecific variability found for the adult Economidis, P.S., and Miller, P.J. 1990. Systematics of round goby is concordant with the pattern found for the freshwater gobies from Greece (Teleostei: Gobi- other neogobiids (sand and bighead) (Simonovicå idae). Journal of Zoology, London 221:125–170. and Nikolicå1995/1996, Simonovicå1996a). Results Erõs, T., and Guti, G. 1997. [First record of bighead obtained for the round goby from the Yugoslav sec- goby (Neogobius kessleri Günther, 1861) in Hungar- tion of the Danube River suggested a sort of cline ian section of Danube] (in Hungarian). Halászat 90:83–84. for its morphology, and confirmed the molluscivory Georgiev, Z.M. 1966. [Some new and little known gob- of that species. A study of resource partitioning be- ies (, Pisces) of Bulgarian ichthyofauna] (in tween the round goby and small-sized native Bulgarian). Izv. NII ryb. stop. 7:159–228. cyprinids in different seasons may help to deter- Harka, Á. 1990. Zusätzliche Verbreitungsgebiete der mine the impact of the round goby on the well es- Marmorierten Grundel (Proterorhinus marmoratus tablished fish communities in the inshore areas of Pallas) in Mitteleuropa. Österr. Fischerei the Danube. 43:262–265. Hegedis˚, A., Nikc˚evicå, M., Micåkovicå, B., Jankovicå, D., ∂ ACKNOWLEDGMENTS and An us, R.K. 1991. 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