Round gobies are small fish with large, frog-like heads, raised eyes, soft bodies, and spineless dorsal fins. Males are generally larger than females. They have a distinctive black spot on their front dorsal fin. Mature round gobies are covered by black and brown splotches that lighten when threatened. Round gobies are distinguished from sculpins by their fused pelvic fin, which is also called a suctorial disc and is used to help attach to a surface in flowing water.
Round gobies have been introduced in several areas outside of their native range. They are an invasive species in the Great Lakes region of North America, with a rapidly expanding range there. Round gobies are beginning to enter the river drainages of the Great Lakes, including the Chicago River, eventually resulting in the invasion of the Mississippi River drainage. (Sapota, 2006)
Bottom dwellers in the nearshore region of lakes and in rivers, round gobies prefer rocky habitats that provide lots of hiding opportunities. These habitats also include areas with sunken objects, piers, and mussel beds. Round gobies can be found in fresh or brackish water and at depths of 0 to 30 meters. They can survive in water temperatures of 0 to 30 degrees Celsius, but tend to thrive in warmer waters. Round gobies are able to survive in areas with poor water quality. They can also withstand low oxygen concentrations. Both of these qualities made them well-suited to surviving in ballast water, which is how they were introduced in the Great Lakes. (Fuller, et al., 2007; Jude, 1995; Marsden and Jude, 1995; Pascualita, 2008; Sapota, 2006)
There is almost no larval stage in the development of round gobies. Eggs take up to 18 days to hatch. (Sapota, 2006)
Males guard nests and attract females to spawn there. Multiple females may leave their eggs in a single male's nest.
Female round gobies spawn repeatedly, approximately every 20 days, from April until September while males guard the eggs and young. This repeated spawning gives them an ecological advantage over species which spawn less frequently. Females are mature by 2 to 3 years of age and males at 3 to 4 years. Females deposit 89 to 3841 eggs at a time. Fecundity is directly related to female body size. Eggs are laid on a hard substrate, such as gravel, rocks, or even submerged trash, and are then guarded by the male until hatching. (Marsden and Jude, 1995; Sapota, 2006)
Round gobies are extremely aggressive fish for their size. They will attack other fish to drive them away from an area. They are solitary, although there may be many of them in a small area. They do not travel far, generally staying in one place. Their swimming is characterized by short, darting movements, making it look as if they are "hopping" between hiding places. They generally stay near the bottom of the water. They may make very small, local migrations to deeper water in fall and back to shallow water in spring, but these migrations are only up to several kilometers in length.
Round gobies remain in very small home ranges.
Round gobies, like most other fish, use visual and chemical cues in communication. They have a complete lateral line system that helps them to hunt in dark water or at night. (Sapota, 2006)
Round gobies are voracious feeders. Up to 60% of their diet is made up of mussels in some places. They also eat aquatic insect larvae, the young and eggs of other fish, and aquatic snails. In the Great Lakes they prey on zebra mussels, another Great Lakes exotic from the same native region. They can eat up to 78 zebra mussels each day. A complete lateral line system allows them to feed in complete darkness. In the Great Lakes they also eat the young and eggs of mottled sculpin, logperch, darter species, and lake trout, among other species, making them a threat to those native populations.
Their hop-like swimming style and blotchy coloration that helps them blend in with their surroundings are defenses against predators. Round gobies are eaten by large, predatory fish and diving and wading birds.
Round gobies compete with native species where they are introduced. In the Great Lakes, they compete directly with similar fish, such as mottled sculpin, which they completely displace from spawning and foraging areas. They also compete with, and eat the young and eggs of, logperch and darter species.
Because round gobies often eats bivalves that filter the water, they are vectors for bioaccumulation of many contaminants. The contaminants that build up in round gobies are passed on to larger game fish and then possibly on to humans. Round gobies are a threat to native fish species, which they drive out of preferred habitat and compete directly for prey. Round gobies are a nuisance to anglers who lose their bait to them. (Ghedotti, et al., 1995)
In its native region of the Black and Caspian Seas, round gobies are prey fish for economically important food fishes, and are also fished for food. In the Great Lakes, they feed on zebra mussels, another exotic species that causes a host of problems. It does not reduce the concentration enough to control these mussels, though. (Ghedotti, et al., 1995)
As an invasive species in the United States, efforts to reduce round goby populations are underway. They have no special status in their native range, though their cousins, tubenose gobies, which are also invasive in the Great Lakes, are endangered in the Black Sea region. (Jude, 1995)
Tanya Dewey (editor), Animal Diversity Web.
Rebecca Hayes (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.
Fuller, P., A. Benson, E. Maynard. 2007. "Apollonia (Neogobius) melanostomus" (On-line). USGS Nonindigenous Aquatic Species Database. Accessed December 10, 2008 at http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=713.
Ghedotti, M., J. Smihula, J. Smith. 1995. Zebra mussel predation by round gobies in the laboratory. Journal for Great Lakes Research, 21: 665-669.
Jude, D. 1995. Two New Fish Aliens in the Great Lakes. Center for Great Lakes and Aquatic Sciences Factsheet University of Michigan.
Marsden, J., D. Jude. 1995. Round gobies invade North America. Great Lakes SeaGrant Factsheet, FS 065.
Pascualita, S. 2008. "fishbase.org" (On-line). Accessed December 10, 2008 at http://www.fishbase.org/summary/SpeciesSummary.php?id=12019.
Sapota, M. 2006. "NOBANIS – Invasive Alien Species Fact Sheet – Neogobius melanostomus" (On-line). Online Database of the North European and Baltic Network on Invasive Alien Species. Accessed December 11, 2008 at http://www.nobanis.org/files/factsheets/Neogobius_melanostomus.pdf.