Teug is acclimating to it's new environment. Sudden changes a multitude of things. It can be mood, lighting, oxygenation levels, or all. Some polys will keep their external gills even when larger.
No way really? I've never seen a large poly with external gills. But she's about 4.5 inches?? I've never raised a juvi poly before so I'm new to this haha. Maybe that's why she's been taking been long gulps/breaths and now it's kind of slowed down?
Any other non poly tank mates? When a young poly feels threatened. The gills will either stay around longer or become pronounced.