This is an adult Blue Tang at night. This Blue Tang is sleeping in the reef at a depth of 30 feet. Blue Tangs change color at night. Adult Blue Tangs are a solid blue during the day, but at night change into a pattern of blue and white vertical bars. Blue Tangs take shelter in the reef at night. They will sleep alone in a hole or crevice in the reef. This Blue Tang has found shelter between a white branching coral and an orange barrel sponge. Do you think the Blue Tang's white bars give it camouflage while it sleeps next to the branches of the coral?
Blue Tangs also change color as they grow old. Juvenile Blue Tangs are actually bright yellow all over. As they get older, they gradually turn blue. Adolescent Blue Tangs are a light blue. Old Blue Tangs are a very dark blue.
This Blue Tang was sleeping at a reef called The Library on the west coast of the island of Grand Turk. The Library reef is just offshore from the island's library, which gives the reef its name.