Round Goby

The Round Goby (Neogobius melanostomus) is a bottom-dwelling fish in the family Gobiidae, native to the Black Sea, Caspian Sea, and Sea of Azov basins of Eastern Europe and Western Asia. Since the late 20th century, it has become one of the most widespread invasive fish species in North America's Great Lakes and connected waterways, as well as parts of Western Europe, likely spread via ballast water from cargo ships. It is a hardy, adaptable species that thrives in both freshwater and brackish conditions, tolerating a wide range of temperatures and substrates. Its rapid spread and aggressive competition with native bottom-dwelling species have made it a focus of considerable ecological research and monitoring in invaded regions.

• Body: robust, blunt-headed, mottled olive-gray to brown, typically 10-18 cm
• Marking: a distinct black spot on the rear portion of the first dorsal fin, a key identifying feature
• Fins: pelvic fins fused into a single sucker-like disc on the belly, used to grip substrate
• Eyes: large, protruding, positioned high on the head

The fused pelvic disc and dorsal fin spot together distinguish the Round Goby from native sculpins and darters, which have separate pelvic fins and lack this marking. Its blunt, frog-like head profile is also more pronounced than in most native look-alikes.

In its native range, the Round Goby occupies the Black Sea, Caspian Sea, and Sea of Azov, along with connected river systems. In its invasive North American and Western European range, it has established itself in the Great Lakes, connecting waterways, and several European rivers, favoring rocky, gravel, or sandy bottoms in both fresh and brackish water. It tolerates a wide temperature and salinity range and can be found from shallow nearshore areas down to moderate depths, often sheltering under rocks or debris. Its adaptability to varied substrates and water conditions has been a major factor in its rapid spread beyond its native basin.

Round Gobies are primarily nocturnal bottom-dwellers, sheltering under rocks or debris during the day and becoming more active at dusk and night. They are aggressive and territorial, particularly males guarding nest sites in rock crevices during the breeding season, which can extend over several months with multiple spawning events. Males guard and fan the eggs, deposited on the underside of rocks, until hatching. The species feeds opportunistically on small invertebrates, including mollusks and insect larvae, and in invaded ecosystems it competes aggressively with native benthic fish for food and shelter, a key factor in its status as an invasive species of ecological concern in the Great Lakes region.