Fu manchu liong get much bigger than 4 inches. They are considered a dwarf lion, but get to be about 6-8". You could definintly put him in a 55 though. Just an FYI thoguh, Lions are like dogs of the fishtank.... they eat alot and s*it alot too. If you put more than one in a tank, you might have a problem with water quality. I have a Dwarf lion as well in my 55. I was pissed though, b/c the week after i got him, my LFS got a FMC lion!!! grr.....