Any way you view it, a pot-bellied 14-inch “seven-striper” from North America is one impressive yellow perch. But show us a true 20-incher—a fish Swedish angler Tomas Helge Sköld calls ‘perchzilla’—and American anglers might just drop what they’re doing and hop on the next flight abroad. The transformation of a species began about 100 million years ago. As tectonic plates shifted and separated North America from Eurasia, once-related plant and animal species found themselves at opposite ends of the globe.…