was searching board for info on gill cover, plates...found this thread
my current batch is being grown from smalls, when very small i couldn't easily see the short gill plate on a couple, but as they grew a little i could, as they grew bigger, i REALLY could. the ones with full a operculum kept it, the ones with short are staying short. it just is more obvious now that they are larger.
argentum, did anything change w/ yours?