When I was around 10 years old I discovered that with my 5mw laser pointer. Even though it might sound silly to some I kinda worry for the fish. I used to have a few small saltwater aquariums and all my little buddies were kinda expensive to be blinding them. Like I said I dont know how it would affect them. But yeah it was still pretty fun. I used to do it to schooling fish. Maybe I might try it again haha.