I know that a lot of people like petting their fish, however, it is not something I would actually advocate. You've got to be aware that a fishes skin is covered by a protective membrane. It is very important that this membrane is not damaged at all, if it is, then diseases can penetrate the fishes skin which could put its health at risk. So if you are going to touch the fish, do it very gently, and don't do it too much. I would also make sure that your hands are very clean before putting them in the tank water
