Round gobies have established large non-native populations in the Baltic Sea, several major Eurasian rivers, and the North American Great Lakes.

The eyes are large and protrude slightly from the top of the head and, like most gobies, the pelvic fins are fused to form a single disc (shaped like a suction cup) on the belly.

They are also found in the rivers of Crimea and the Caucasus (Mezib, Pshada, Vulan, Kodori, and Çoruh) and in the Caspian Sea, represented by subspecies Neogobius melanostomus affinis.

Since 1990, the round goby has been registered as introduced in the North American Great Lakes, in parts of Europe, and in the Baltic Sea as an invasive species.

[7] In the same season, near the Romanian coasts of the Black Sea, the round goby feeds on polychaetes, crustaceans (Idotea balthica, Pachygrapsus marmoratus, Xantho poressa, etc.

In the Great Lakes, they also eat the young and eggs of Cottus bairdii, Percina caprodes, Etheostoma spp., and Salvelinus namaycush, among other species, making them a threat to those native populations.

Males also use visual displays, including posturing and changing color from beige to black during mating season, and can produce sounds during courtship.

First discovered in North America in the St. Clair River in 1990, the round goby is considered an invasive species with significant ecological and economic impact.

An aggressive fish, the round goby outcompetes native species such as the sculpin and logperch for food (such as snails and mussels), shelter, and nesting sites, substantially reducing their numbers.

The goby's robust ability to survive in degraded environmental conditions has helped to increase its competitive advantage compared to native species.

[23] It is now distributed all along the southwestern Baltic Sea coast, including Stettiner Haff (Szczecin Lagoon), the Unterwarnow (Warnow river estuary), the mouth of the Trave, and the Nord-Ostsee (Kiel) Canal.

As of 2010, the westernmost site of round goby occurrence in Europe was the lower Scheldt, including the tidal zone in the river mouth, and Albert Canal, Belgium.

[26] The most abundant parasites of the Black Sea round goby are metacercariae of trematodes of the Heterophyidae family, such as Cryptocotyle concavum, C. lingua, and Pygidiopsis genata.

[28][29] In the 1950s, along the coast of the Gulf of Taganrog (Sea of Azov), the round goby was registered as a host of epizootic nematodes Tetrameres fissispina and Streptocara crassicauda, which were fatal to ducklings.

[38] The parasite "load" on the invasive gobies in the Great Lakes appears relatively low in comparison with their native habitats, lending support to the "enemy release hypothesis".