This is an adult Blue Tang swimming above the reef at a depth of 30 feet. Blue Tangs are a species of surgeonfish. Surgeonfish have a sharp spine at the base of their tails. This spine is as sharp as a knife, and can be used to attack other fish. Blue Tangs eat algae, and are usually seen in the daytime browsing and poking at the reef for tidbits of food. Young Blue Tangs are very territorial, and may use their sharp spines to chase away other Blue Tangs to protect their 'crop' of algae. The Blue Tangs' spines are bright yellow. You can see the yellow spine on the Blue Tang in this photo.
Blue Tangs can change color. 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. Old Blue Tangs also lose their aggressiveness. Although younger Blue Tangs are loners, old Blue Tangs are often seen in large schools.
Blue Tangs take shelter in the reef at night. They will sleep alone in a hole or crevice in the reef. At night, adult Blue Tangs change color by showing a pattern of blue and white vertical bars.
This Blue Tang was swimming above a reef called Conch Bar Reef on the west coast of the island of Grand Turk.