Its definatly a synodontis spicese. could be one of the more common ones like nigriventis although these spend a lot of time up side down (hence there common name up-side down cat) or it could be a fether fish syno. eupterus. can't see any markings on the photo.
It looks like a syno. eupterus - I've got one and it looks just like that. The the fishy equivalent of a vacuum cleaner. Eats anything and everything , mainly nocturnal and spend quite a bit of their time upside down. Have you ever seen yours skim just under the surface of the water (upside down of course) vacuuming in any food there?
About 8" long and 6" round the girth of it's belly Big, fat, messy fish but great characters and great clean up guys. Adults can get a bit terratorial and they do need quite a large tank. How big is your tank?