I wouldn't do them in anything less than a 55g (Unless you have some weird shaped 40 or 50 breeder that has a 4' footprint but isn't quite as tall). They need lots of room to swim because they are so active. Even though they are smaller than the huge catfish, they still get 5"-6", and they do prefer to be kept in a group of their own kind, about 5-6 or so. I do love this catfish too though, and hope someday to have a tank for them as well.
Emily