Do you mean the Mekong River Giant Catfish, Pangasianodon gigas? The largest ever caught was something like 9 feet long and 646 pounds, and they are an endangered species.
Just get a paroon shark (pangasius sanitwongesi) basically the same size. Also gigas are algae eaters.......so if you got a big one, what you gonna do? Feed it a 50 lb algae wafer ?