It looks very much like a loach, but I'm afraid it may be a barbel (as in, the british gamefish). The people at the pet store insisted it was a Synodontis catfish, but I've had 3 tropical aquariums over the last couple of years and know better.
Sorry if the pics are huge and hard to make out. He seems to like flakes but hasn't gone for gardenworms or mosquito larvae. He was $20.
He is about 4-6 inches (bad at guesstimation) and mostly black.
gaaa I feel silly now. I hadn't known black sharks had whiskers. I probably bought it for way too much. It's in a 55 gallon with 3 large angelfish and 5 little zebra danio.