I keep an MBU-puffer in my stingray tank. It has been there for about three months without any problems. Now its about 10 inches. I just love the puffer, as I love my rays and I really enjoy how they seem to get along so well. At feeding time my big leo-male sometimes jump on top of the puffer. But he does not hurt the puffer, and the puffer doesnt seem to mind, going on with his business. Im afraid that the puffer one day will turn on one of the rays. Is it a big risk? Do any of you have any experience with well behaved puffers suddenly turning on a ray?