and those gizzards are about twice as slimy as anything else out there!What djamieson said, "Someone told me the easiest way to tell is by looking at the lips. If the lower lip juts out further than the upper lip it's a hickory. And if they're more or less even it's an American. Is that right?
The jutting of the hickory's lower lip is pronounced and easily observable. But you might need to close their mouths before this is obvious.
The other shad: I've lost track of the number of fishermen at Chain Bridge I've observed crank in a huge snagged gizzrd shad and proudly decree it to be an American shad. The mouths of gizzard shad is located slightly under their nose. Gizzard shad also have a very long last filament to their dorsal fin that trails back along their back. To see this extra long filament, you will need to stand up the dorsal fin. Sometimes its 1.5 to 2" longer than the other rays on the dorsal fin. Plus, gizzard shad are much more drab than either hickories or Americans.