Just today one of my yellow tangs started swimming vertically for brief periods . It almost looks like it is posturing. Kind of looks like my clown when she is spawning. The video shows it mostly in the corner but it does do it in the middle of the tank. Some times it flares its fins that really looks like posturing. I also noticed it is pretty much staying in the one half of the tank and not swimming past half way. It does do it when one of the other tangs are not near also. I just fed and it ate. That's when I noticed it. All other fish are normal. I've never seen this behavior so need to know if its something I need to be concerned about.