A dark spot on the dorsal fin is common. Round Goby – The distinctive feature of the round goby is its fused pelvic (bottom) fins. This fish can grow up to 10 inches in length, although 3- to 6-inch fish are more common. The smaller tubenose goby has two, rather distinct, tube-like projections from its head. Map courtesy of U. S. Geological Survey. The round goby is a small, but aggressive bottom-dwelling fish that grows rapidly, and reproduces several times in one spawning season. It is a huge threat to North American aquatic ecosystems because it is adaptable to a wide range of environmental conditions, and will eat just about anything alive that will fit in its mouth. Species Description Round gobies have a soft body and a large round head with thick lips and distinctive frog-like raised eyes. They can reach up to 10 inches in length as adults, but are usually less than seven inches in the Great Lakes. Females and immature males are a solid slate gray mottled with black and brown spots. Spawning males turn almost solid black. Two distinguishing characteristics of round gobies are a single, scallop-shaped pelvic fin and a distinctive black spot located on the dorsal fin. Round gobies closely resemble the native mottled sculpin, but the two species can be easily separated by looking at the pelvic fins. The sculpin has two separated pelvic fins compared to the single, fused pelvic fin found on the round goby. The sculpin also lacks the large black spot found on the dorsal fin of the round goby. Native & Introduced Ranges Round gobies are native to Eurasia in the Black, Caspian, and Azov seas, and tributaries. They were first discovered in the St. Clair River in 1990, presumably released during ballast water exchanges of transoceanic ships. They have since spread to all of the Great Lakes, and are now working their way inland through rivers and canal systems. In Pennsylvania, the round goby is abundant in Lake Erie and its lower tributaries. The first inland occurrence for Pennsylvani
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