It's difficult when they are very young, but if you see enough of them you can tell by the color: On the juvenile queen angel, the trailing edge of both the dorsal and anal fins next to the tail have a very bright neon blue spot on each fin while the blue has a blue edge to the fin but not the bright blue spots. Also, sometimes the bars on the blue are more straight while the queens vary between curved and straight. And, one some of the queens, particularly the older juveniles, the
[hr]
and crowns have much more bright blue than the blue angels. If it seems that the fish you are looking at doesn't seem to have as much brilliant blue "trim" as you'd like, then it's probably a blue angel. As both fish age, the amount of blue trim on the queen really stands out more than the blue...
Both fish are exquisite though :thinking: