From the Chicago News Cooperative:

When University of Wisconsin-Milwaukee professor John Jannssen found a round goby in Calumet Harbor in 1994, he feared the worst. The small fish with an almost endearing wide-eyed stare reproduces prolifically and eats voraciously. Jannssen and other scientists expected it to gobble up the eggs of prized sport fish and hog the mussels and snails that other fish would normally eat.

Today millions of round gobies are thriving in the waters of Lake Michigan off Chicago and throughout much of the Great Lakes. But as is often the case with invasive species, their ecological impact has not been devastating, but complicated–even beneficial in some cases. Read more.