OOOoo I love my blue crawfish. He is the most awsome thing in my tank. Anyways I have had much success keeping him with tiger barbs, cherry barbs, zebra danios, CAE
,a snail that came from who knows where, and buenes aires tetras. Fish that are fast swimmers without fancy fins are good. The crawfish actually move kind of slowly when they are hunting so a faster fish can easily escape them. They are also really good scavengers.