Round goby (Neogobius melanostomus)

Synonyms: Gobius melanostomus, Apollonia melanostoma

Description:

Round goby (Neogobius melanostomus) is a small bottom-dwelling fish from the Black and Caspian Seas of Eurasia that reached the Great Lakes in ships' ballast water and was first found in 1990 in the St. Clair River [1][2]. It spread to all five Great Lakes within a few years and is an aggressive competitor that crowds out native bottom fish and eats their eggs [2][3]. MISIN tracks it because it spreads through bait-bucket release and is now one of the most abundant fish in parts of the Great Lakes [3].

Identification:

Round goby is a small, soft-bodied fish, usually 3 to 6 inches long (sometimes up to 10 inches), with a large, blunt head and frog-like eyes set high on top of the head [2][3]. Its body is gray to tan with dark brown or black blotches, and there is a distinct black spot at the back of the first (spiny) fin on its back [3]. The surest way to identify it ? and to tell it from native bottom fish ? is to look at the underside: the round goby's pelvic fins are fused into a single, scallop-shaped suction cup, while native sculpins and darters have two separate pelvic fins [2][3].

Round gobies are easiest to notice in the warm months, from spring through fall, when they are active in rocky shallows and constantly grab at anglers' bait [3]. During the spawning season the males turn almost entirely black, which makes them especially easy to spot [2].

At-a-glance cues:

1. Pelvic fins fused into a single suction-cup-like fin on the belly (native sculpins have two separate ones) [2][3]
2. A distinct black spot at the back of the first fin on the back [3]
3. Small gray-to-tan body with dark blotches and a large, blunt head with raised eyes [2][3]
4. Breeding males turn almost entirely black [2]

Habitat:

Round goby is native to the Black, Caspian, and Azov Seas of Eurasia and was carried to North America in the ballast water of ocean-going ships [1][2]. After turning up in the St. Clair River in 1990, it spread to all five Great Lakes and into many connecting rivers and tributaries [2][3].

It is a bottom fish of shallow, rocky and weedy areas of lakes and large rivers, and it also uses sandy bottoms [2]. Part of what makes it such a successful invader is its toughness: it tolerates both fresh and brackish water, a wide range of temperatures, and poor, low-oxygen water that many native fish cannot handle [2].

Reproduction:

Round gobies reach new waters almost entirely because of people. The fish first arrived in ballast water, but within the region the biggest risk is anglers using them as live bait and then dumping the bait bucket; they also hitch rides on boats and gear [2][3]. Because of this, round goby is illegal to use or possess as bait in many places [3].

Once established, round gobies breed fast. Females can spawn several times in a season (roughly every few weeks from April through September), laying their sticky eggs on the undersides of rocks, shells, and other hard surfaces [2]. The males turn black, guard the nest aggressively, and then die after the spawning season [2]. This rapid, repeated breeding lets the fish build very large populations quickly, so the key to limiting it is preventing its spread to new waters [2][3].

Impact and Damage:

For people, round goby is not a health hazard, and the most direct nuisance is for anglers: gobies aggressively grab bait, making it hard to catch the fish you actually want [3]. The deeper problem is what they do to native fish and the food web [3].

Round gobies are aggressive and reach very high numbers ? more than 20 fish per square meter in some places ? and they take over the rocky habitat that native bottom fish need [2]. They outcompete and displace native sculpins and darters; one study documented a local population of mottled sculpin disappearing after round gobies arrived [4]. They also eat the eggs and young of native and sport fish such as smallmouth bass and lake trout [2][3]. Round gobies feed heavily on invasive zebra and quagga mussels, and through that link they are tied to outbreaks of avian botulism (type E): a toxin can pass from mussels to gobies to the fish-eating birds that eat them, killing large numbers of waterbirds [2][3].

Similar species:

Round goby is mistaken for several native bottom fish, so check the belly fins and the dorsal spot.

Mottled sculpin (Cottus bairdii) is the closest look-alike ? a native bottom fish of similar size and blotchy color ? but it has two separate pelvic fins rather than the round goby's single fused, suction-cup fin, and it lacks the black dorsal spot [2][3].

Logperch (Percina caprodes) is a native darter that lives on the bottom in similar places, but it is slender with a pointed, pig-like snout and dark vertical bars, and it too has separate pelvic fins [2].

Slimy sculpin (Cottus cognatus) is another native bottom fish confused with round goby, but like other sculpins it has two separate pelvic fins and no black dorsal spot [2].

Tubenose goby (Proterorhinus semilunaris) is a smaller invasive goby that also has a fused pelvic fin, but it is told apart by the short tube-like nostrils that project out over its upper lip [2].

Monitoring and rapid response:

Signs to watch for:

1. Small bottom fish that constantly grab your hook or bait in rocky shallows [3]
2. A gray, blotchy fish with a single suction-cup-like pelvic fin on the belly and a black spot on the first fin on its back [2][3]
3. Almost entirely black fish (breeding males) around rocks in the warm months [2]

What you can do:

1. Never use round goby as bait and never release it ? dispose of unwanted bait and any goby you catch in the trash, not back in the water [3].
2. Learn to tell round goby from native sculpins by the single fused (suction-cup) pelvic fin, so you do not move it by mistake [2][3].
3. Clean, drain, and dry your boat, trailer, livewell, and gear between waterbodies, and never move water or live fish from one lake or river to another [3].
4. Report any round goby you find, especially in a new lake or river, so agencies can respond quickly [3].
5. Across the Great Lakes, agencies rely on ballast-water rules, monitoring, and barriers to slow the spread, but there is no known way to remove established round goby populations from open water ? which is why prevention is so important [3].

When to call a professional:

1. Round goby found in a lake, river, or any water connected to other waterbodies, where it cannot be contained [2][3]
2. Any situation that would involve barriers, ballast-water management, or large-scale monitoring, which are agency-led efforts [3]
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. Integrated Taxonomic Information System (ITIS). Neogobius melanostomus (Pallas, 1814) ? TSN 172072. itis.gov
2. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Neogobius melanostomus (round goby) ? Species Profile. nas.er.usgs.gov
3. Minnesota Department of Natural Resources. Round goby (Neogobius melanostomus). dnr.state.mn.us
4. Janssen J, Jude DJ (2001). "Recruitment failure of mottled sculpin Cottus bairdi in Calumet Harbor, southern Lake Michigan, induced by the newly introduced round goby Neogobius melanostomus." Journal of Great Lakes Research 27(3):319?328. doi.org/10.1016/S0380-1330(01)70647-8

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