hmmm, just put a few of them in with a few paroon sharks, and wells. I think you would have the most awesome giant cat tank around. Better get at least a 50,000 gal. like the one someone tried to play off that he had. I am sure they would be quite happy in there. Once they all get to 9ft you could just feed them road kill, and for the mekongs just dump in 100's of pounds of algae wafers everyday. Seriously would the mekong not be an extremely hard fish to raise. You would need to make an algae aquarium just to feed them. 

I heard that you can saddle one up and ride it over the moon.