Blue Tang (night coloration)
Acanthurus coeruleus

f16 @ 1/60s, ASA 64, Ektachrome slide film, Nikonos II w 28mm and Nikon close-up lens, Oceanic flash

"Acanthurus," Wikipedia, the free encyclopedia. Acanthurus is the type genus of the family Acanthuridae. Approximately half of all members of the family are members of the genus Acanthurus. They are found in tropical oceans, especially near coral reefs, with most species in the Indo-Pacific, but a few are found in the Atlantic Ocean. As other members of the family, they have a pair of spines, one on either side of the base of the tail, which are dangerously sharp (hence the name "surgeonfish"). Depending on species, they grow to a maximum length of 1550 cm (620 in). Many are very colourful and consequently popular in the marine aquarium trade.
Frederiksted Pier at night, St. Croix, U.S, Virgin Islands