Although gobies belong to a family of fish with a worldwide distribution in both salt and fresh water, they had not been found in the Great Lakes prior to 1990. The round goby first turned up in Lake Superior's Duluth/Superior harbor area in 1995. Presumably, the fish arrived in ballast water discharged by trans-oceanic ships.
It can be difficult to distinguish between round gobies and sculpins, but the goby's fused pelvic fin is the best way to tell them apart. Round gobies are bottom-dwelling fish that perch on rocks and other substrates. They are aggressive fish and voracious feeders. They will vigorously defend spawning sites in rocky or gravel habitats, thereby restricting access of other less aggressive fish to prime spawning areas. Gobies also have a well-developed sensory system that enhances their ability to detect water movement. This allows them to feed in complete darkness, and gives them another advantage over other fish in the same habitat.
Also native to the Black and Caspian seas region, its cousin, the tubenose goby, appeared for the first time in the St. Clair River in 1990; however, this species--which is endangered in its native habitat--has remained uncommon in the Great Lakes.
Gobies also are capable of rapid population growth. They spawn repeatedly during the summer months, and each time, a female can produce up to 5,000 eggs. The males die after spawning.
In Europe, the diet of round gobies consists primarily of bivalves (clams and mussels) and large invertebrates, but they also eat fish eggs, small fish and insect larvae. In the United States, studies have revealed that the diet of round gobies includes insect larvae and zebra mussels.