The round goby is a small, bottom-dwelling invasive fish. Native to the Black and Caspian seas in Eastern Europe, it was first found in North America in 1990 in the St. Clair River north of Windsor, Ontario. Researchers believe the fish was brought to North America in the ballast water of ships from Europe. In less than a decade the round goby has successfully spread through all five Great Lakes and has begun to invade inland waters. In some areas the fish has reached densities of more than 100 fish per square metre.
Round goby have reduced populations of sport fish by eating their eggs and young, and competing for food sources.
To prevent the spread of this invasive species, the Ontario government has banned the possession of live round goby and the use of round goby as a baitfish.
http://docs.files.ontario.ca/documents/3202/stdprod-104406.pdf