Mandarin fish is one of the popular subject for underwater photographer because of the striking beauty color and interesting habit (they went out mating during sunset everyday :P). It can be a tricky photographic subject, coming in and out of view, appearing only briefly at dusk to mate and seemingly wishing to avoid any bright light.
Mandarin Fish Fact Sheet
Family name: Callionymidae
Order name: Perciformes
Common name: Mandarinfish
Scientific name: Synchiropus splendidus