There are two main kinds of big aquatic salamanders, hellbenders and mud puppies (or waterdogs, as they're also known). Both kinds eat small fish, crawdads, and aquatic insects. Hellbenders are the biggest, getting up to 2 feet long or better, and they have big, wide mouths and a flattish head. They are rapidly becoming an endangered species over much of their range for reasons not completely understood, but it may have to do with water quality and chemical contamination. Hellbenders do not have external gills as adults. Water dogs or mud puppies do have external gills, they don't get nearly as big (maybe 12-14 inches maximum), and they have narrower heads and smaller mouths. In Ozark streams, I've caught mud puppies on live minnows while fishing for walleye. They seem to have the habit of attacking minnows by grabbing their bellies and clamping onto them and chewing until they wear a hole in the belly, because I've reeled in a lot of minnows with chewed up bellies in areas where mud puppies are common. It also seemed that if the mud puppies were out and about, the walleye weren't, because I almost never caught a walleye on a day when the mud puppies were biting. I suspect big walleye really like to eat mud puppies!
Touring Kayak Paddles