FIRST RECORD OF THE ROUND GOBY , NEOGOBIUS MELANOSTOMUS ( ACTINOPTERYGII : PERCIFORMES : GOBIIDAE ) IN BELGIUM

Almost six years after the first finding of the round goby Neogobius melanostomus (Gobiidae) in the Netherlands, several specimens of this invasive Ponto-Caspian benthic fish were also recorded in the Belgian part of the River Scheldt and in the Albert Canal. This is the first record of the round goby in Belgium.

The round goby Neogobius melanostomus (Pallas, 1814) is a benthic, euryhaline species o f the family Gobiidae, native to central Eurasia including the Black-, Azov-, and Caspian seas.Maximum standard length is 25.0 cm but smaller sizes are attained in fresh waters (Pinchuk et al. 2003).Diagnostic characteristics o f the round goby following Pinchuk et al. (2003) include a completely scaled nape w ith cycloid scales on the anterior and middle nape (also upper opercle, breast, pectoral fin lobes, and part o f abdomen with cycloid scales while the rest o f the body has weak ctenoid scales), head depth about equal to width, a lateral line typically with 49-55 scales, pelvic disc with weakly defined lateral lobes on anterior membrane usually not reaching anus, dorsal fins contiguous and second dorsal fin uniform in height.Most conspicuous is the prominent posterior black spot on the first dorsal fin.This spot does not occur in other Ponto-Caspian gobies except in Neogobius caspius (Eichwald, 1831).The latter species, however, can be easily distinguished from the round goby by e.g., ante rior nostrils very close to the upper lip and a lateral line w ith 58-71 scales (Pinchuk and Miller 2003).
The Ponto-Caspian round goby was transported with ballast water to different parts o f Europe and North America (Corkum et al. 2004).In the Netherlands, van Beek (2006) reported the first record in 2004 and recent fish surveys have shown that the species is now w ide spread and abundant in the Dutch Rhine and Meuse delta (Spikmans and van Kessel 2010).The only other westem-European country w ith populations o f N. melanostomus seems to be Germany where it occurs in the river Danube and in the Baltic Sea (Kottelat and Freyhof 2007).Other (North, Central and East) European countries with records o f introduced round goby include Austria (Mühlegger et al. 2010), Poland (Grabowska et al. 2010), Czech Republic (Lusk et al. 2010), Hungary (Borza et al. 2009), Slovakia (Stráñai and Andreji 2004), Bulgaria (Polacik et al. 2008), Serbia, Romania, Estonia, andSweden (Froese andPauly 2010).
The round goby was recorded for the first time in Belgian waters in the tidal, mesohaline part (three to four pro mille salinity at the time o f sampling) o f the River Scheldt near Liefkenshoektunnel (lat 51°17'27.75"N,long 4°18'05.74"E)(Fig. 1) on 8 April 2010.The first specimen found measured 10.5 cm total length (TL) (Fig. 2) and was caught in a paired fyke net.The fykes were placed in the River Scheldt in the framework o f a fish monitoring pro gramme o f the Research Institute for Nature and Forest.Only two months after this discovery, 12 specimens o f the round goby were caught by an angler on three occasions (8, 15, and 24 June 2010) in the Albert Canal near Hasselt (approx.lat 50°56'59"N , long 5°19'18"E) (Fig. 1).Two of those 12 specimens mentioned above were given to the first author (9.3 and 10.6 cm TL, respectively).The remaining ones were photographed and released.On 29 June 2010, another specimen (5.2 cm TL) was caught in a fyke net in the River Scheldt near Zandvliet (lat 51°22'57.3"N, long 4°14'15.52"E)(Fig. 1).
The first caught specimen was carefully examined and identified as the genus Neogobius following Miller and Vasil'eva (2003) and further diagnosed as N. melanosto mus following Pinchuk et al. (2003).The morphometric characteristics and meristics o f this specimen o f N. melanostomus (Table 1) were similar to those reported in the literature (Pinchuk et al. 2003).This specimen has been deposited in the Royal Belgian Institute o f Natural Sciences (Brussels, Belgium) as reference material (1 spec imen, 105.1 m m TL, location: Liefkenshoektunnel, Scheldt, collection reference: KBIN 24.768).
While ballast water transport was an important vector for the rapid spreading o f the round goby over long dis tances, also active migration was suggested as a coloniza tion route.This was facilitated by the opening o f the Main-Danube Canal in 1992 which connected the Rhine and Danube river systems and thus enabling Ponto-Caspian species to move actively to West-Europe (Copp et al. 2005).As in the Netherlands (van Beek 2006), it is likely that round gobies were released in the lower part o f the River Scheldt (within the proximity o f the international har bour o f Antwerp) with ballast water disposal.It cannot be ruled out, however, that also active migration o f specimens from the dense populations in the Dutch Rhine delta through the Rhine-Scheldt Canal (Fig. 1) has taken place.The specimens recorded in the purely freshwater Albert Canal almost certainly must have reached there as a result o f natural dispersal as there is no transport o f sea vessels.The distance between the locations on the lower River Scheldt and the Albert Canal is about 100 km making active migration (Komis and Vander Zanden 2010) a pos sible explanation even with three ship locks in this section.It is unlikely that the round gobies were used (illegally) by anglers as live bait and released after fishing.The catches o f 12 round gobies by an angler in the Albert Canal suggest that this gobiid is probably already abundant in certain parts o f this canal.The Albert Canal constitutes the main corri dor between the two largest river systems in Belgium namely the Rivers Meuse and Scheldt.Hence, we predict that due to the strategic position o f the Albert Canal a wide distribution o f round goby in Belgium will soon be a fact.
The introduction o f N. melanostomus has caused eco logical as well as economical problems with well docu mented cases for the Laurentian Great Lakes (USA and Canada) and for the G ulf o f Gdansk (Poland) (for an overview see Corkum et al. 2004).M ain concerns expressed by Corkum et al. (2004) are: -transfer o f contaminants through the food web; -detrimental effects on native species; -proliferation due to multiple-spawning habits; -potential expansion by anglers through use as live bait; and -economic costs o f gobies as bycatch in nets o f com mercial fishery.Dorenbosch (2009) suggests that the decline of native bull head populations of Cottus perifretum Freyhof, Kottelat et Nolte, 2005 and Cottus rhenanus Freyhof, Kottelat et Nolte, 2005 in the Dutch River Rhine since 2000 may be related to a rapid increase in numbers of the Ponto-Caspian gobiids there.Apart from the round goby, other gobiid species from the Ponto-Caspian region may be expected in the near future in Belgium (Verreycken et al. 2007)  In order to reduce the establishment, expansion and impact o f non-native and invasive species in Belgium, a draft o f the Royal decree on the import, export, transit and possession o f invasive alien species was prepared in 2009.This decree prohibits the possession and transport o f live specimens o f some invasive non-native species in Belgium e.g.Amur (or Chinese) sleeper Perccottus glenii Dybowsky, 1877 and also the round goby.However, this proposal has not been endorsed yet.Hopefully it will soon as was the case in the N etherlands where w estern tubenose goby, Proterorhinus semilunaris (Heckel, 1837), settled in the Dutch Rhine system in 2002; round goby in 2004; bighead goby, Ponticola kessleri (Günther, 1861), in 2007; and monkey goby, Neogobius fluviatilis (Pallas, 1814), in2009 (van Kessel et al. 2009).

Fig. 1 .Fig. 2 .
Fig. 1.Locations o f first records o f Neogobius melanostomus in Belgium ( • ) with indication o f main rivers and canals

Table 1
Meristics and morphometric characteristics (as percentage o f indicated measurements) o f the first Neogobius melanostomus specimen caught in Belgium in the Scheldt River near Liefkenshoektunnel (lat 51°17'27.75"N, Note: Spinous rays in Roman letter type, articulated rays in Arabic letter type.