Speaking from experience (after having foolishly listened to an otherwise normally informed employee at my LFS) - the blue crays love to redecorate, and no matter how well fed they are, they WILL attack/kill/eat any fish that gives them the opportunity. Mine was ok during the day, but when the fish settled in after lights went out... I had swordtails, bolivian rams, and I honestly don't remember what else in that tank, and he killed at least one from every group in his couple days in that tank and did substantial damage to many others.
They also get very large. Mine doubled in size in the couple of months it took to find him a new home. They are cool critters, but they don't play well with others, they pretty much need a species tank.
