me thinks moving more as needs more water and oxygen through gills goin on what was previously said.
didnt look to me like gill curl in the early pics.
looked just like mine does when he opens his gills then they flatten down again as he closes them . i dont think mine has gill curl and he seems more than happy.
just for info = if he stops moving his tal or it seems straighter due to the more movement now required. ==== dont be tempted to cut that off too !! lol . ( same goes for all fins and head too . )