I had a crayfish that got pretty big years ago. When you have a crayfish, no fish is safe unless he is much bigger. My crayfish would climb up on a big rock in the middle of the tank. He would stick his claws out, spread apart and pincers open. Then he would freeze. He would remain completely still laying in wait. When an unsuspecting fish would swim by he would grab it in a flash and hang on for dear life. Needless to say, I had to eventually get rid of him. Not sure if CPO crayfish have such a nature, but they are meat eaters if they can get it.