Issue
Knowl. Manag. Aquat. Ecosyst.
Number 420, 2019
Topical Issue on Fish Ecology
Article Number 13
Number of page(s) 5
DOI https://doi.org/10.1051/kmae/2019006
Published online 11 March 2019

© S. Zogaris et al., Published by EDP Sciences 2019

Licence Creative Commons
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The racer goby Babka gymnotrachelus (Kessler, 1857) is native to the river catchments of the Black, Marmara and Caspian seas (Miller & Vasil'eva, 2003). Since the mid 1990s, this goby has invaded several central European rivers although it has not been recorded in Balkan rivers that enter the Mediterranean (Piria et al., 2017a; Koutsikos et al., 2019). Here we report on the recent discovery of B. gymnotrachelus in the transboundary Evros-Maritza-Meriç basin (hereafter Evros, the classical name), the largest river in the Balkans after the Danube. The Evros has been called an “open-door” for invading alien species (Ozulug et al., 2018); that is, human-assisted species dispersal which drift downstream of Bulgarian entry points. This dispersal pathway concerns species introduced from Bulgaria's Danubian and Black Sea basin freshwater fauna. In recent years another non-native Ponto-Caspian goby, the Pontian monkey goby Neogobius fluviatilis (Pallas, 1814) was documented in Bulgarian (Stefanov et al., 2008) and Greek parts of the Evros basin (Zogaris and Apostolou, 2011) but despite several sampling visits, the population in Greek waters was not re-located (Economou et al., 2016; Zogaris et al., 2018) and no new non-native gobies were recorded in this river until now.

During September 10th 2018, 13 specimens of B. gymnotrachelus were collected on routine EU Water Framework Directive (EU WFD) fish monitoring within Greek territory in the Evros. Electrofishing surveys are undertaken with a five-meter aluminum boat that holds a generator-powered direct-current electrofisher (EFKO, 8 kW, 150–300/300–600 V) with a hand-held netted ring anode of 40 cm diameter (effective electric field of about 2.5 m diameter). This method catches fishes along the banks and at depths of down to about 1.7 m. At least 400 m of river stretch within Greek territory was sampled at each survey site; however, benthic habitats in deeper waters were out of reach. All stunned fish were collected by the netted anode and by a second operator using a separate dip-net. After measurement and identification nearly all specimens were released alive back to the river. In this survey, non-native gobies were collected, photographed in a field aquarium, anaesthetized (using clove oil), humanly euthanized and fixed in a 98% ethanol solution for lab study (Fig. 1).

B. gymnotrachelus was found at sampling sites “Evros_MD” near Nea Vissa village and at “Evros_UP” near Ormenio village (Fig. 2). Additionally, at “Evros_MD” and at the southernmost site, “Lykofos”, N. fluviatilis was re-located; this species was first discovered in Greek territory 24 river kilometers downstream of “Lykofos” in 2011 (Zogaris and Apostolou, 2011). A tributary site, “Erythro_DW” had no gobies; although native gobies have been found in many other tributaries (Dimitriou et al., 2012). B. gymnotrachelus specimens were collected in a variety of habitats, including muddy backwaters and deeper water near rocky groynes. The fish community in the sampled areas was rich (13–20 species per site) and the native western tubenose goby Proterorhinus semilunaris (Heckel, 1837) was by far the most abundant goby (Tab. 1).

B. gymnotrachelus specimens were identified (based on: Miller and Vasil'eva, 2003; Kottelat and Freyhof, 2007; Vassilev et al., 2012) by the following characteristics:

  • the lack of a black spot on the posterior part of the first dorsal fin versus a visible black spot in Neogobius melanostomus (not present in this river);

  • the first branched ray of the second dorsal fin is about as long as the penultimate ray versus the second dorsal branched fin ray, being twice as long as the penultimate ray in N. fluviatilis;

  • a more roundish head versus a more flat and broader head in Ponticola kessleri (not present in this river) and versus the narrower pointed head of N. fluviatilis, and;

  • areas without scales on the nape (this area feels very smooth when touched as compared with N. fluviatilis, where nape scaling gives a relatively rough texture).

In addition, the sides of B. gymnotrachelus often show a characteristic but variable slanting striped pattern. Since sexual maturity occurs after the second year of life, at an approximate total length (TL) greater than 5.8 cm (Grabowska, 2005; Cocan et al., 2016) only specimens from “Evros_MD” had reached reproductive sizes (Tab. 2). The 8 specimens from “Evros_UP” includes young-of-the-year juveniles, providing first evidence that the species probably reproduces and is therefore established in the area. The possibility of young-of-the-year fishes being recently introduced by humans at this location is highly unlikely, and this is corroborated by the older individuals collected at Evros_MD, which is 46 river kilometers downstream. All collected specimens were stored in the HCMR Fish Museum at Anavissos, Greece.

B. gymnotrachelus and other related Ponto-Caspian goby species have been assessed as “invasive” in the Balkan countries (Simonović et al., 2013), however this species' invasion progress has been poorly recorded (Roche et al., 2013; Jakšić et al., 2016; Piria et al., 2017b). Caution is needed in tracking, identification and invasiveness assessments of Ponto-Caspian gobies since even hybridization among invaders is a possibility, although probably extremely rare (Haertl et al., 2012; Lindner et al., 2013). In our case, hybridization with sympatric gobies is highly unlikely but genetic analyses and further study is recommended in order to research the provenance and mode of entry into the Evros river basin (e.g. Ohayon and Stepien, 2007; Grabowski et al., 2016). In our opinion natural dispersion into the Evros by B. gymnotrachelus is inconceivable, despite the fact that this river is geographically close and historically related to the Black/Marmara Sea catchments that host native populations of this and other Ponto-Caspian gobies. We hypothesize that the probable vector for invasion is the accidental transfer through fish stocking practices from the Danubian/Black Sea catchments to the Evros's Bulgarian artificial dam reservoirs. Fish stocking and unintentional angler-associated translocations are frequent in the Bulgarian part of the basin and several freshwater organisms have entered Greece and Turkey through this transboundary river (İnnal and Erk'akan, 2006; Barbieri et al., 2015; Ozulug et al., 2018). The Bulgarian part of the Evros basin has several large reservoirs, including hydroelectric dams and it is well-known that these attract amateur fishing activity were fish introductions are poorly regulated (Stefanov et al., 2008). Large numbers of young-of-the-year fishes, including alien gobiids, are known to pass through hydroelectric dam turbines and overflows (Janáč et al., 2013). Reservoir development with stocking and amateur fishing are a primary route of entry of many invasive species of fish in the Mediterranean: river basins (Clavero and Hermoso, 2011; Koutsikos et al., 2019) and elsewhere (Johnson et al., 2008).

The Evros's B. gymnotrachelus record is especially important because it provides: i) first evidence of what we presume to be an early stage invasion process; ii) preliminary data that the native P. semilunaris is still the most abundant goby relative to the other two non-native Ponto-Caspian gobies (at least in the shallower waters and river banks sampled); and, iii) possible indication of a downstream dispersal from Bulgaria of B. gymnotrachelus (the juvenile specimens at “Evros_UP” were collected literally c. 20 m. from Bulgarian territorial waters). However, this report also shows the inadequate degree of ichthyological monitoring by the three countries sharing the Evros river. Additionally, boat-based electrofishing on its own may not be adequate for quantitative surveys of benthic gobies and other methods should also be employed (Szalóky et al., 2015; Lenhardt et al., 2017). Moreover, it is noteworthy that B. gymnotrachelus has been overlooked and its establishment status was undefined until recently even in several Danube tributaries (Roche et al., 2013; Piria et al., 2017b); the species is probably overlooked in the Bulgarian and Turkish stretches of the Evros also. This species should obviously be present in the Bulgarian part of the Evros but there are no published records to our knowledge (Vassilev et al., 2012; Yankova, 2016). Biological pollution problems such as the expansion of non-native Ponto-Caspian gobies, which are a potential pressure on biotic communities (Roche et al., 2013), is also a reason for international cooperation in monitoring and management of this important transboundary river (Dimitriou et al., 2012; Trebitz et al., 2017).

Acknowledgements

The monitoring project is supported by the Special Secretariat for Water, Ministry of Environment and Energy and by European Union funding. We thank D. Kommatas who shares responsibility in the boat-based electrofishing unit and E. Dimitriou who heads the WFD monitoring project at HCMR. We are grateful to colleagues in Bulgaria and Turkey who assisted us with their knowledge of this shared river.

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Cite this article as: Zogaris S, Ntakis A, Barbieri R. 2019. The racer goby, Babka gymnotrachelus (Kessler, 1857) invades the Evros river: evidence of recent establishment in Greece. Knowl. Manag. Aquat. Ecosyst., 420, 13.

All Tables

Table 1

Total number and size classes of gobid fishes caught at four surveyed sites.

Table 2

Babka gynotrachelus total length (mm), sex and location (MD = Evros_MD, UP = Evros_UP).

All Figures

thumbnail Fig. 1

Cropped photograph of Babka gymnotrachelus from Evros_MD site (93.5 mm TL). Photographed alive on-site in a field aquarium after application of clove-oil anesthetic.

In the text
thumbnail Fig. 2

EU WFD boat-based fish monitoring sites on the Evros river.

In the text

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