The U.S. invasion brought about by the crown prince

When Crown Prince Akihito visited Chicago on October 3, 1960, his sole request was to visit Shedd Aquarium. Then Mayor Richard J. Daley, an avid angler, presented the prince with a gift that he scooped with a net from one of the tanks himself: 18 bluegills, the official Illinois state fish. [...] But in the meantime, the fish thrived unnoticed in the wild, multiplying in Japan's rivers, lakes, and streams, expanding its diet beyond insects, plankton, and aquatic plants to shrimp and native fish eggs. In their North American habitats, bluegills reproduce quickly and live for a long time, whereas in Japan, native shoreline fish had temporarily kept the bluegill population under control by eating their eggs and juveniles. By 1999, the bluegill had colonized all freshwater ecosystems in the country, spurring government-supported research into bluegill dispersal. But by then, it was way too late.

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