ID Black dots on yellow tang?

[Delphinus]

How big is he Danny?

If he's small enough, get an empty Coca-Cola 2l bottle, rip off the label, cut off the top, rinse it etc. and put it in the tank with some mysis or other favourite food. Yank it out when he swims into it (you'll only get 1 or 2 shots at this before he clues in).

If he's too big for a pop bottle trap, maybe get some clear acrylic or glass even for baffles, whatever you may have lying around or whatever is easiest to get ahold of, and then corral him into the pop bottle or net.

Good luck!