Juvenile Blue Tang in nighttime coloration
Acanthurus coeruleus

1/60s at f16, Ektachrome 64, ASA 64, Nikonos II w 28mm lens and close up lens, Oceanic flash

"Blue Tang," Reef Fish Identification, Florida, Caribbean, Bahamas by Paul Humann and Ned Deloach. Can change from powder blue to deep purple, and pale to dark. Dorsal and anal fins edged in bright blue. More circular than other surgeonfishes. Can be solitary, but more often in large aggregations foraging about shallow reef tops, grazing on algae. Schools can include Surgeonfish and Doctorfish.
Frederiksted Pier, St. Croix, U.S. Virgin Islands at night