yeah, a mbu can take apart a crayfish/crawfish, depending on the size of the crayfish. If the crayfish is so big, it can tear apart your mbu...use discretion 
any photos of the beast?IME, mbus don't swim constantly unless they are trying to beg for food.They may sit on the ground passively until something attracts their attention, usually their owner or in-tank activity. My 22-inch mbu will swim back and forth along the front of its 8-foot x 3-foot home when it wants me to feed it.
is the temperament on the mbu more agressive or the fahaka?
