This week, we launch “Chesapeake: A Journalism Collaboration” with other public radio stations in the bay watershed. And we do it with a look at catfish; not those ugly little bottom feeders with whiskers, but their larger—much larger—cousins, blue catfish. A few years ago, scientists worried this invasive species threatened other creatures in Chesapeake tributaries. So, a seafood wholesaler has appropriated a slogan from previous fish invasions --eat ‘em to beat ‘em—and begun aggressively