Synodontis nigriventris is the most commonly seen Upside Down Catfish and has taken the common name, however, there are other species that have the same characteristic; the much rarer Synodontis contractus and the vicious Asian Upside Down Catfish, Mystus leucophasis.
In the wild these fish can been seen in large shoals much like Corydoras, so they should be kept accordingly if you want them to be active. A dimly light tank and many retreats make an excellent home for a group of these fish, they fit perfectly into most community tanks aswell. They will eat most of the prepared and live foods available. Best of luck