no-dont do it
crayfish/yabbies all stalk and attack fish, usually while sleeping at night in a crevice...Ive tried it, and it doesnt work...yabbies make great pets, but must be housed alone (no fish, and no other yabbies either, they fight)...you might get away with tetras, or some other mid water schooling fish, but any fish that shelters in your rockwork at night will be fair game for your cray...
your cray will eat anything...as long as it sinks to the ground...I used to feed my yabbie steak (keep a small bit in the freezer and just chop off small pieces), on a skewer...keep your fingers away from their claws!!! Also, sinking veggie tabs are good for them
OT-what sort of cichlids are they?