Round goby

Neogobius melanostomus

Order: Gobiiformes

Family: Gobiidae

Genus: Neogobius

The round goby is a small, bottom-dwelling fish with a robust body and a distinctive fused pelvic fin that forms a suction cup-like disc, allowing it to anchor to rocks and surfaces in fast-moving water. Adults range from 6 to 25 centimetres in length, with mottled grey, brown, and black markings that help them blend into rocky lakebeds. They have large, bulbous eyes set high on their head and a slightly protruding lower jaw. Males turn almost entirely black during the breeding season and become aggressively territorial.

Originally from Eurasia, this species was introduced to the Great Lakes in the 1990s, likely via ballast water from ships. Since then, it has spread rapidly through connected freshwater systems.

Conservation Status: IUCN

Distribution

Native: Coastal regions of the Black and Caspian Seas
Invasive: Great Lakes Basin (including Lake Ontario), St. Lawrence River, inland tributaries in Ontario, Québec, and several U.S. states

Habitat

Prefers rocky bottoms and shallow waters of lakes, rivers, and harbours. Often found near docks, breakwalls, and manmade structures. It thrives in a wide range of temperatures and water conditions, including low oxygen levels, making it a resilient invader.

Diet

Carnivorous and opportunistic. Eats aquatic invertebrates like zebra mussels, small crustaceans, insect larvae, and fish eggs. Its powerful jaws and pharyngeal teeth allow it to crush hard-shelled prey like snails and mussels, contributing to the decline of native invertebrates.

Reproduction

Breeding occurs multiple times during warmer months. Males establish and guard nests under rocks or crevices and attract females with body movements and sounds. A single male may guard eggs from several females. After fertilization, males aggressively protect the eggs until they hatch, often fanning them with their fins to ensure oxygen flow.

Adaptation

Suction-cup pelvic fin allows it to grip surfaces in moving water
Tolerant of low oxygen and variable conditions
High reproductive output helps rapid population growth
Aggressive nest defence increases offspring survival
Diet flexibility helps it outcompete native bottom feeders

Threats to Survival

In its native range, the round goby faces natural predators and ecological limits.
In its invaded range, it has few natural predators and poses more of a threat than it receives. However, predation by native birds and fish is increasing as ecosystems slowly adapt.