URBANA, ILL. Wherever round gobies turn up in large numbers in the Great Lakes and nearby waterways, mottled sculpin-a fish that is the major part of the yellow perch's diet--disappear. The gobies, an alien nuisance fish species similar in size and appearance to the native sculpins, are clearly out-competing them, but how?

One critical factor is that round gobies can interfere with mottled sculpin spawning, according to a study funded by Illinois-Indiana Sea Grant. In effect, the round gobies appear to evict defending mottled sculpins from spawning shelters.

"We tested this theory in an artificial stream and found that when round gobies were added to successful mottled sculpin nest areas, they ate the sculpin egg masses, changed to their spawning coloration and began to defend the sites," said John Janssen, biologist at the University of Wisconsin-Milwaukee.

"By interfering with mottled sculpin reproduction, the round goby may have a negative impact on the food supply of yellow perch, an important sport fish in Lake Michigan. At this point, we don't know whether the round goby will be a part of the yellow perch diet," Janssen added. Yellow perch populations have declined in recent years.

The round goby is native to the Black and Caspian Seas and was probably brought to the Great Lakes in the ballast water discharged from transatlantic ships. Gobies were first spotted in 1990 in the St. Clair River, the channel connecting Lake Huron and Lake St. Clair. Since then, the aggressive, robust fish has expanded its population throughout most of the Great Lakes. Now, experts are concerned that the goby will spread from the Great Lakes water basin to the Mississippi water basin, further affecting North American native species and ecosystems.

Round gobies look very similar to mottled sculpins. Gobies have large heads (as do sculpins) and so they slightly resemble large tadpoles. They are typically about 5 inches long,
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Contact: JohnJanssen
jjanssen@uwm.edu
414-382-1733
National Sea Grant College Program
5-Sep-2001

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