i have a crayfish and he...
i have a crayfish and he is very aggressive to anything in his way. size doesnt matter. mine will not catch live fish. but he will eat it if its dead. i tried putting in feeders and thats what happened. other fish would be ok as long as they stayed off the bottom because he does cut with his big pincers. but he is really neat to watch and he is also an escape artist. make sure you have a good lid with no openings. you would be surprised to see all the things they can climb up-airlines,etc.
