the darkness on top of the heads and in between the verticle stripes could be a sign of stress, mine show darkness in the same area when they aren't relaxed...
bro are you kidding?! those fish look stressed out of there mind! im thinking maybe from a camera flashing a bunch of times. thats why i asked.. but those fish i would say are around 6 to 8 inches or so and those are deff some super dark stress marks for that size fish!