Moon wrasse

The moon wrasse (Thalassoma lunare), also known as the crescent wrasse or lyretail wrasse, is a species of wrasse native to the Indian Ocean and the western Pacific Ocean. It is an inhabitant of coral reefs and surrounding areas at depths from 1 to 20 m (3.3 to 65.6 ft). 
Moon wrasses are carnivores and tend to prey on fish eggs and small sea-floor dwelling invertebrates. This species can reach 45 cm (18 in) in total length. It is part of the aquarium trade.