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. 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. Gobies also are capable of rapid population growth.