Round Goby

Fascinating facts about the Round Goby

• A single round goby can lay up to five thousand eggs, each only 4 × 2.2 mm, and males fan the clutch until hatch, achieving up to 95% success – a reproductive efficiency that helps the species explode in new waters.
• When they first appeared in North America, round gobies were caught on June 28, 1990 in the St. Clair River, and within a few years they spread into tributaries of the Great Lakes and even reached the Hudson River by 2021, showing how quickly a ballast-water hitchhiker can colonize an entire continent.
• Males grow larger than females, reaching up to 24.6 cm (9.7 in) and 79.8 g (2.8 oz), while juveniles stay under one year and are only grey, a striking color shift that signals sexual maturity and territory defense.
• Round gobies tolerate salinities of 18–24% and inhabit depths from 1–2 m to 10–17 m, allowing them to thrive from fresh rivers to brackish seas, which fuels their ability to invade both marine and inland ecosystems.
• In the Great Lakes, round gobies now make up about 90% of the Lake Erie watersnake’s diet and over 86% of lake sturgeon meals in the Niagara River, turning a problematic invader into a critical food source for recovering native predators.

At a glance

About the Round Goby

The round goby (Neogobius melanostomus) is a small, soft-bodied bottom-dweller distinguished by a stark black spot on its first dorsal fin and large, slightly protruding eyes. Adults range from 10 to 25 cm (4–10 in), with males outgrowing females and turning an inky black during the spawning season, their cheeks swelling as they guard nests. Their fused pelvic fins form a suction-cup disc that lets them cling to sandy or rocky substrates on continental shelves, from shallow 1–2 m waters down to 10–17 m, tolerating salinities of 18–24 %. In native basins, Black Sea, Caspian Sea, Sea of Marmara and their rivers, the goby thrives in both fresh and marine settings, feeding nocturnally and diurnally on mollusks, crustaceans, worms, zebra mussels and other benthic invertebrates, even preying on invasive mussels and juvenile gobies. A surprising trait is its dual role as both predator and prey: while it aggressively outcompetes native sculpin and logperch, it also fuels recovery of predators such as lake sturgeon, burbot and the Lake Erie watersnake, which now derives up to 90 % of its diet from gobies. This complex ecological dance fuels its rapid expansion across the Baltic, North Sea, Danube, Rhine and the Great Lakes, where it was first caught on June 28 1990 in the St. Clair River, Ontario.

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