The Round goby originates from the Caspian Sea, the northern parts of the Black Sea and the Sea of Azov (including their tributaries). Today, it is however also found in other parts of the world were it is considered an invasive species and efforts are made to eradicate it in these environments it in order to protect the ecological balance. The Round goby is an adaptable bottom-dwelling fish that can survive in shallow areas of the ocean as well as in brackish and freshwater rivers and lakes. It can over-winter as far down as 60 meters below the surface.
The Round goby (Neogobius melanostomus) is grayish with black, brown, gray and olive green markings. As a juvenile, the fish is gray without markings, except for the characteristic black spot that is located on the front dorsal fin. The body is usually between 4 and 10 inches long in mature specimens and the eyes protrude somewhat from the top of the head. The pelvic fins have developed into a sucking disc. The Round goby is a night active species that feed primarily on smaller fish, fish eggs, crustaceans, mollusks, insect larvae and worms.
The Round goby is a prolific fish, since the female can spawn several times during each spawning season. She will reach sexual maturity when she is between one and two years old, while the males need 3-4 years before they can reproduce. The breeding period begins in April and continues until September. The Round goby is an egg-laying species and the male will protect the nest with the eggs, as well as the hatched offspring. A Round goby egg is typically 4 millimeters long and 2.2 millimeters across.
As mentioned above, the Round goby is today found outside its original habitat. You will for instance find Round goby in all the five Laurentian Great Lakes. You can also find Round gobies in the St. Lawrence River, the Detroit River, the St. Clair River and in Lake St. Clair.
The first recorded sighting of a Round goby in the Great Lakes drainage is from 1990, when an angler caught a Round goby in the St. Clair River in Canada. The Round goby is successfully spawning in Canadian and U.S. waters which make the species hard to eradicate. During the winter of 90/91, 9 juvenile Round gobies were found in Michigan and determined to be no older than one year. Spawning had therefore most likely occurred during the previous summer. Other waters were you will find Round goby in the U.S. are the Shiawassee River, the Chicago River and the Cal-Sag Canal.
In Europe, Poland’s Gulf of Gdansk is experiencing problems with accidentally introduced Round gobies, and the Moscow River, Volga River (Kuybyshev Reservoir) and Aral Sea have also reported cases of Rounded goby. In the Aral Sea, the Rounded gobies were however eradicated during the end of the 1980’s since the salinity of the water rose dramatically due to evaporation and diversion.
The Round goby has probably managed to spread to North America and Europe by means of ballast water in oceangoing ships. Ships traveling shorter distances can continue to spread the species once it has been introduce to an area.