Madtoms are a family of freshwater catfish that are generally only 2-5 inches in length.
Transcript (edited for clarity):
RUDY MANCKE:
Hi, I'm Rudy Mancke from USC for NatureNotes.
Madtoms — you ever heard of them? Smallest catfish species that we've got, and really four in South Carolina.
One's called a tadpole catfish. It's one to five inches, chubby body, terminal mouth, feeds on invertebrates. Pretty good in an aquarium, really. It hides in floating vegetation a lot.
And then speckled madtoms, which nest in bottles and cans on the bottom of streams. Hopefully you're not going to find them down there, but sadly sometimes we do. The first one I found was in a freshwater mussel. I was studying mussels, picked it up, and here was this little speckled madtom.