I have a plecostamus that is about 20 years old and 18” long. I’m the past few weeks, he started developing some kind of growth on the side of his head, just under his eye but not covering his Gill. I worry that this is some kind of tumor. It has grown fast the last couple of weeks. He doesn’t act like it bothers him or affects him right now. But I’m just going by his normal behavior which really hasn’t changed. I worry about how serious this is because of his age. Can you offer any advice?