Black tang - Zebrasoma rostratum
It is the two blackfishes one in the center and the other in the lower left side of the picture. You can discern their white tail spine and their protruding snout. The smaller black fishes above are damselfishes, Dascyllus trimaculatus and there is also a moorish idol at the right bottom part. In the background there are mostly Anthias and Blunt-headed wrasse juveniles.
''Zebrasoma rostratum'', the longnose surgeonfish or black tang, is a marine reef tang in the fish family ''Acanthuridae''. They may live at water depths of 10–61 m or more. The fish grow to a maximum length of 21 cm. Zebrasoma rostratum is found in the South Pacific off the coasts of the Society Islands, Marquesas Islands, Line Islands, Tuamoto Islands to the Pitcairn Islands.