Blue Tang (night coloration)
Acanthurus coeruleus

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

"Blue Tang," Wikipedia, the free encyclopedia. A surgeonfish usually found in the Caribbean and the tropical Atlantic Ocean.
Frederiksted Pier at night, St. Croix, U.S. Virgin Islands