I have kept regular crayfish but never the blue kind, but either way they are peaceful and will only mess with small fish that are slow enough for them to catch. You really need to worry about the cichlid you choose, I used to feed my Oscars crayfish as snacks and they would only last seconds in the tank, so you want to make sure it is not a fish that will eat it (when it gets large enough) or will constantly pick at it and eat the legs and claws of it. So as far as American cichlids go, your best bets would be most of the dwarf cichlids such as the Pandas, Rams, Cockatoos, etc. Also Keyholes, Acaras and Severums would probably work fine.

MFK