The round goby (Neogobius melanostomus) is the latest potential nuisance invader to the Mississippi River Basin's ichthyofauna. Like the zebra mussel, the round goby is now becoming established in the Great Lakes and may soon find its way into the Mississippi River Basin through the Chicago Ship and Sanitary Canal and down the Illinois River to the rest of the Basin. Its biology was described at a February 21-22 conference in Chicago organized by the Illinois Natural History Survey and Illinois-Indiana Sea Grant. Round Gobies were first found in North America in the St. Clair River, just south of lake Huron, in 1990, along with the tubenose goby (Proterohinus marmoratus). Both species are native to the Black and Caspian seas. Tubenose gobies are "endangered" in Russia, but the Russian application of that definition is unknown. Both species have thrived in the St. Clair River and in Lake St. Clair downstream, where Michigan Dept. of Natural Resource trawl surveys catch them in large numbers.

The round goby has established two additional centers of distribution, in which it is abundant and spreading. These are Calumet Harbor on southern Lake Michigan, and the Grand River, a tributary to the central basin of Lake Erie. In all three location, round gobies are caught in large numbers by anglers, sufficient to make angling for perch and walleye difficult (tubenose gobies are not being caught by anglers). Round gobies are said to be good tasting, but bony. They are a major nuisance for anglers in Lake St. Clair, but are a good fish for kids, because they are so easy to catch. The largest specimens in the Great Lakes have been about 180 mm (7 inches), but they get larger in their native range.

Round gobies have also been collected in Lake Superior (two specimens in Duluth Harbor in 1995) and Lake Huron (one specimen taken at Goderich, Ontario by and angler and photographed in 1994). A sighting in eastern Lake Ontario was made in 1995 by a qualified scientist, but no specimen was collected, so the sighting is treated as unconfirmed. So far, no round gobies have been found on the Mississippi River basin side of the Chicago Ship and Sanitary Canal. However, Illinois plans to look for them in 1996. Round gobies have a fascinating, and not completely understood, life history. Females mature at one year of age, as small as 58 mm, and spawn every 20 days, up to six times, during the spring. Total fecundity is about 5,000 eggs. The eggs are cone-shaped and adhesive, clinging to rocks and other structure. Males guard the nests, and turn dark black when spawning. Males are said to die after spawning, but this may not always be the case. Males can live to be 5-6 years old. One hypothesis suggested to explain data on sex ratios and maturity is that females turn into males a year or two after spawning! Round gobies are benthic throughout their life, even when newly hatched. As they grow, round goby diets switch from small benthos (chironomids and crustaceans) to mollusks. They eat large numbers of zebra mussels, about 70-80/day. Their pharyngeal teeth are ideal for crushing shells. They are selective for small zebra mussels, less than 9 mm in length. Round gobies 100 mm long can eat zebra mussels up to 15 mm long. Freshwater sponges were found in 1/3 of goby stomachs in one study: sponges are extremely difficult to identify in stomach samples, because they look like partially digested mush. Round gobies eat some fish, and are cannibalistic. Many fish eat round gobies, especially smallmouth bass. Male and female round gobies can generally be externally distinguished by their genital papillae. Round gobies have a distinctive black spot on their anterior dorsal fin, but about 20% of the Lake Erie specimens lack the spot. This appears to be unique in the species. Round gobies are difficult or impossible to age by scales, but Ohio State biologists think it can be done if one looks at many scales from a specimen. Otoliths may be better: University of Windsor biologists are attempting to validate that technique. Impacts on populations of mottled sculpins (Cottus bairdi) are already apparent. There is concern that the lake subspecies of mottled sculpin may be driven to extinction. Other species that may be affected include logperch and lake sturgeon. There is concern about predation on lake trout eggs and fry, but ongoing research by the Illinois Natural History Survey indicates that the mottled sculpin may be a more effective predator on lake trout than the goby. If round gobies colonize the Mississippi River Basin, there is concern about their impacts on darters, several of which are listed on the Federal List of Threatened and Endangered Wildlife. Round gobies are behaviorally aggressive in defending optimal space. They are "smart" enough to turn over rocks to look for prey. They are larger than most competing species, feed in total darkness by sensing prey with their ultra sensitive lateral line system, and they tolerate poor water quality. All of these factors give them competitive advantages over native species. Last summer, Minnesota Sea Grant recommended in writing to the Aquatic Nuisance Species (ANS) Task Force that the round goby be declared an aquatic nuisance as defined by law, and that a control program be developed. The ANS Task Force responded that more information is needed, and there is a clear process that must be followed.

Condensed from River Crossings, May-June 1996