Has anyone ever seen a fish that once was normal, fast swimming etc, develop a problem with their back end? I had a mollie who one day didn't want to move his tail. He could move it if he HAD to (if he was being bothered etc) but he would just let it hang...almost like it hurt him to move it. Eventually he died (probably of exhaustion of just using his front fins) but I was told it didn't sound like a disease or sickness, but that is sounded like nerve damage. Is this anything anyone has heard of??