Mbuna Cichlids love to eat crayfish--given a chance
After reading the recommendation about removing the crayfish , I remembered what happened to me a few years ago when I had one in my 130 gallon tank. Because they go through a molting process as they grow--- and to do this they burrow under the substrate or into a cave and pull subtrate to cover the opening while this takes place, they are then very vulnerable until the new exoskeleton hardens.
One morning I woke up and had to do a double-take as I walked by my tank. I had a pretty large electric yellow hap that was swimming around with a large blue claw hanging out of his mouth -- almost seemed like he was "parading" around the tank with pride that he had this prize.
Sure enough -- as I looked around the floor of the tank, around rocks, etc. I saw other evidence of the carnage. They had evidently ganged-up on the crayfish during the night after un-covering his hiding place, and then literally ripped him to shreds in his un-protected state.
wouldn't want to see you have the same experience. Move the crayfish to another tank with less a less agressive species present.