Male purple queen anthias (Pseudanthias tuka). This gregarious fish inhabits reefs in the tropical Indian and western Pacific Oceans. It feeds on small crustaceans, plankton and fish eggs, and can reach a length of around 12 centimetres. Males are discernible by the dark purple colouration at the base of the dorsal fin. Photographed off Derawan Islands, East Kalimantan, Indonesia.