The Round Goby, Neogobius melanostomus, is a small bottom dwelling fish that is usually between eight and fifteen centimeters long. Adults are a light gray color with mottled brown, black, and olive blotches over their body with a white underside. Juvenile Round Gobies have a solid gray body. The posterior part of the first of their two separated dorsal fins has a distinct black spot. They are covered in fine scales and have a terminal mouth opening (Frohnauer et al., 2018). Gobies have large heads with bulging eyes as well as a long, torpedo-shaped body. A feature that distinguishes Round Gobies from native North American fish is their single, fused, suction cup-like, pelvic fin.

Systematics:

Round Gobies are in the family Gobiidae. Recent phylogenetic analysis has shown that Gobiidae is a sister group to Butidae, Eleotridae, Rhyacichththydae, and Odontobutidae (Adrian-Kalchhauser et al., 2017). Round goby, Neogobius melanostomus, is in the Neogobiini tribe, which is one of three tribes within the Benthophilinae subfamily. The Benthophilinae diverged from the Gobiidae family. This subfamily includes gobies which are native to the Ponto-Caspian region. A tribe is a taxonomic group above genus but below subfamily The Neogobiini tribe includes only  the Neogobius genus. The genus Neogobius consists of gobies native to the Black and Caspian Seas. Within the genus there are four species: N. caspius, N. fluviatilis, N. pallasi, and N. melanostomus. Neogobius pallasi was once thought to be a subspecies of N. fluviatilis, but has been reclassified as a separate sister species (Neilson et al., 2009). The Neogobiini clade consists of N. caspius being a sister species to N. melanostomus and N. fluviatilis which can now be split into N. fluviatilis and N. pallasi.

The Round Goby is an invasive species that has spread from Eurasia to the Great Lakes of North America as well as the Baltic Sea, and Moscow River (Charlebois et al., 2001). The goby was most likely transported from the Black Sea, the Caspian Sea, or the Gulf of Gdansk through the ballast water of shipping containers. It was first described in the Great Lakes in 1990 and has since spread to every Great Lake as well as several of their tributaries and the Flint, Shiawassee, and Saginaw rivers in Michigan. It has started moving down the Chicago Sanitary and Shipping Canal towards its connection with the Mississippi River.

The Round Goby is able to thrive in a wide range of habitats, allowing it to proliferate when introduced to new bodies of water (Charlebois et al., 2001).  It is a benthic fish and has caused a decline in native benthic fishes. Recent study has shown that the Round Goby has been expanding its habitat from just nearshore rocky habitat and tributaries, to more open waters of the Great Lakes (Clapp et al., 2001). They prefer a habitat with many hiding spaces that can also be used as nesting sites (Skora et al., 2001).

Food: In Europe, Round Gobies feed primarily on mollusks such as various freshwater mussels and clams (Charlebois et al., 2001). However, they have been observed competing with native fishes in the Baltic Sea feeding on crustaceans, polychaetes, as well as bivalves (Skora et al., 2001). As in its natural habitat, it feeds on epibenthic organisms and benthic species that became abundant during different seasons. However, in the Great Lakes region, the Round Goby has also been reported eating zebra mussels, Dreissena polymorpha, an invasive freshwater mussel (Charlebois et al., 2001).  Round Gobies could have a greater impact on zebra mussel populations than native fish species (Djuricich et al., 2001).

Adrian-Kalchhauser, I., Svensson, O., Kutschera, V. E., Rosenblad, M. A., Pippel, M., Winkler, S., & Burkhardt-Holm, P. (2017). The mitochondrial genome sequences of the Round Goby and the Sand Goby reveal patterns of recent evolution in gobiid fish. BMC genomics, 18(1), 177.

Charlebois, P. M., Corkum, L. D., Jude, D. J., & Knight, C. (2001). The Round Goby (Neogobius melanostomus) invasion: current research and future needs. Journal of Great Lakes Research, 27(3), 263-266.

Clapp, D. F., Schneeberger, P. J., Jude, D. J., Madison, G., & Pistis, C. (2001). Monitoring round goby (Neogobius melanostomus) population expansion in eastern and northern Lake Michigan. Journal of Great Lakes Research, 27(3), 335-341.

Corkum, Lynda D., Andrew J. MacInnis, and Robert G. Wickett. "Reproductive habits of round gobies." Great Lakes Research Review 3.2 (1998): 13-20.

Djuricich, Paul, and John Janssen. "Impact of Round Goby predation on zebra mussel size distribution at Calumet Harbor, Lake Michigan." Journal of Great Lakes Research 27.3 (2001): 312-318.

Frohnauer, N. Galatowitsch, S. Larkin, D. Montz, G. Phelps, N. Plude, T. Weber, M. 2018. AIS Identification Guide Second Edition. Minnesota Aquatic Invasive Species Research Center.

MacInnis, Andrew J., and Lynda D. Corkum. "Fecundity and reproductive season of the Round Goby Neogobius melanostomus in the upper Detroit River." Transactions of the American Fisheries Society 129.1 (2000): 136-144.

Neilson, Matthew E., and Carol A. Stepien. "Escape from the Ponto-Caspian: Evolution and biogeography of an endemic goby species flock (Benthophilinae: Gobiidae: Teleostei)." Molecular Phylogenetics and Evolution 52.1 (2009): 84-102.

Skora, Krzysztof E., and Jadwiga Rzeznik. "Observations on diet composition of Neogobius melanostomus Pallas 1811 (Gobiidae, Pisces) in the Gulf of Gdansk (Baltic Sea)." Journal of Great Lakes Research 27.3 (2001): 290-299.