Another recent invader causing considerable concern is the a small bottom-dwelling fish with a large head resembling that of a tadpole. First discovered in Lake St. Clair in 1990, presumably introduced via ballast water from transoceanic vessels, the round goby and the tubenose goby have spread to Lakes Erie, Michigan and Superior and to many rivers, including the Mississippi watershed. Round gobies are thriving in the Great Lakes Basin because they are aggressive, voracious feeders that can forage in total darkness. The round goby takes over prime spawning sites traditionally used by native species competing with native fish for habitat and changing the balance of the ecosystem.
- Length:4 to 10 inches (250 mm)
- Coloring: grey with blotches of black and brown over their bodies, dorsal fin may be tinged with green, the front dorsal fin has a distinctive large black spot
- Common Names: Round goby, goby
- Found in Lakes: Michigan, Huron, Erie, and Superior
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.
Also native to the Black and Caspian sea 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.