This is definitely a unicornfish, a fish part of the genus Naso. Unfortunately, I'm unable to identify this fish completely, maybe (Naso unicornis), since they are common in aquaculture? Other fish pictured here that I was able to identify include Bluering Angelfish (Pomacanthus annularis) and Royal Blue Tang (Paracanthurus hepatus).
Some species from the genus Naso. Naso unicornis seems likely but cannot confirm since the distinctive blue caudal spines are not visible in the photo. The fish behind the unicornfish is a Porkfish, the one above the Royal Blue Tang is a Redtail Butterflyfish. The fish behind the Royal Blue Tang is Barred Spinefoot and the two resting on the substrate are some spinefoot species.
