The smallest species of shovelnose cat regularly found in fish stores is Sorubim lima,they grow to at least 12" and may grow to 20",all other species of shovelnose will reach at least 24" and possibly 48".They are all predators and will eat any fish they can fit un their mouths,which are huge.But they are not aggressive and can be housed with any non aggressive fish that is at least the same size as them.
I have two S.limas and keep them with some large bala sharks earth eater cichlids some medium sized cats and other non aggressive predators,they are fed on meaty frozen foods (mussels cockles and fish) and catfish pellets for predatory catfish,normal pellets are not suitable.They also take all the usual live foods such as bloodworm and shrimp.