Round goby (mustakitatokko) – Neogobius melanostomus

The round goby is a bottom-dwelling fish that does not have a swim bladder and which is active when the light is low, and at night. It lives mostly in shallow water, where reproduction takes place during the summer months. Females lay their oval eggs in clusters in rock crevices. Once the male has fertilised the eggs, he stays to guard them. Round goby tolerates poor water quality, with oil present and in oxygen-poor conditions. For the winter, it finds waters that are slightly deeper.

The large black spot on the first dorsal fin, which is lacking in other goby species, is the identifying feature of round goby. Its base colour is usually pale, but there are darker spots or patches on the sides and back. However, males are almost black during the spawning season. The round goby resembles the black goby, as both have fused pelvic (bottom) fins, typical for gobies, and two dorsal fins very close to one another. In five years, it can achieve a length of around 25 cm, double that of the black goby.

The round goby is native to the Black Sea and Caspian Sea regions, from where it has spread to new water areas in ships' ballast waters or as eggs attached to the hull. The species was observed for the first time in the Baltic Sea on the coast of Poland in 1990. It was simultaneously found in the Great Lakes in North America. In Finland, the first reported observation was in winter 2005 in Kaarina and the following ones in Helsinki in spring 2009. Until now, the species has been detected in the nearby waters of 12 ports on the Finnish coast. 

In its native range, the round goby is a food fish, and could become so in Finland. In Poland, cod and cormorants have begun to feed on round goby.

Tämä laji on vieraslaji, jota ei ole säädetty haitalliseksi eli se ei kuulu kansalliseen eikä EU:n haitallisten vieraslajien luetteloon, ja esimerkiksi lajin myynti ja kasvattaminen ovat edelleen sallittuja. Kaikkia vieraslajeja koskee kuitenkin vieraslajilain mukainen ympäristöön päästämisen kielto ja siksi niihin on syytä suhtautua varauksella.

The species is an aggressive competitor, and if it becomes more common, it may result in losses in the original range of fish species due to competition for nutrition and space. It is established almost everywhere it has been observed. In some rivers and coastal areas in central Europe, the round goby has become the dominant species. Competition over nutrition is possible with the flounder (Platichthys flesus) and other species feeding on zoobenthos. The round goby has been proven to proliferate so intensely, that densities of dozens of individuals per square metre are common. This enables them to efficiently feed on the eggs and fry of other fish. When abundant, round gobies take to the baits of anglers greedily. In the Great Lakes, they have thus been found to hamper the fishing of other perciforms.

In Finland, the black goby (Gobius niger), European bullhead (Cottus gobio) and viviparous eelpout (Zoarces viviparus) may lose not only nutrition but also protection and breeding sites to round gobies. In Helsinki, the black goby is almost non-existent in places occupied by the round goby. In the future, the round goby may interfere with fishing for other species, including the net fishing of herring and vendace. Because the round goby potentially feeds on fish eggs and fry, it may threaten the fish stock of inland waters if it gains access to the Vuoksi waterway through the Saimaa canal.

The round goby has spread quickly along the Finnish coast, and no preventive measures have been undertaken. The Ballast Water Management Convention should be adopted immediately. Round goby can be fished using traditional fishing methods, such as angling or ice fishing. Fish traps, nets and trap nets can also be used. In inland waters, the most effective fishing method is electric fishing (subject to special authorisation). Individuals may not be transferred or used as bait in areas where the species is not yet present.

Saaliiksi saatua mustatäplätokkoa ei tule palauttaa veteen.

Tee mustatäplätokkohavainnosta ilmoitus Luonnonvarakeskukselle kalahavaintolomakkeella.

• Sapota, M.R. (2012). NOBANIS- invasive Alien Species Fact Sheet - Neogomius melanostomus. From Online Database of the European Network of Invsive Alien Species - NOBANIS www.nobanis.org. Date of access 2016-05-02. (PDF) 
• Joki, Niklas 2016. Vieraista meristä Itämereen löytänyt kala valtaa alaa Suomessa – "Aggressiivinen etenkin kutuaikaan", jossa asiantuntijoina Rikka Punttila sekä Teemu Tast.  Toimittaja: Niklas Joki. Yle Uutiset Kotimaa 2.5.2016