I don't know for sure, that's just what first popped in my head when I saw your picture. You could try googling a bunch of images of sergeant majors, and see if it looks like any of them.
that's definitely not a sergeant major. even the smallest of them have the evenly spaced lines. whatever it is, I have one in a tank with sergeant majors both larger and smaller and there is an obvious difference between the two species when they're next to each other. If i come across its name I'll be sure to put it up.
Perhaps it is a hybrid or misbarred carribean sargent? The aspect that is throwing me off is the dark head and 6 stripes. All of the sargent pictures I've seen have light heads and 5 stripes. The one you posted appears to have a 6th stripe that encompasses the top of the head. The scissortail damsel has this feature, but your picture doesn't show the dark tail streaks that the scissortail has. Also important to consider is location since this was found off of key west. Perhaps send the picture to wetwebmedia and see if they can identify it?
I've caught 8 very tiny juvies in the last week living among the pin fish and sergeant majors, glad to know what they are finally!:claphands:claphands Thanks!!!