The Harlequin sweetlip (Plectorhinchus chaetodonoides) is a small species of fish that is found in coral reefs between 1 to 30 meters of Indian Ocean and the central-western Pacific Ocean: Bali New Guinea, Sumatra, Great Barrier Reef, Philippines, Mauritius Islands, Maldives Islands, New Caledonia, Vanuatu Islands.
Plectorhinchus, means “muzzle with folds” while chaetodonoides indicates “has the appearance resembling to a Chaetodon.”. Sweetlips are also called “grunts” from the fact that they can use their specialized teeth in the back of their throats, to make a grunting sound.
This fish is mainly nocturnal. The young usually hide amongst corals in lagoons in the daytime, while adults are found solitarily in caves and under rock overhangs. Usually, they feed at night on shrimp, crabs, snails, worms, and small fishes.
Juveniles are quite appealing and is easily distinguished by its pattern; brown with large white patches edged in black and white-and-black fins. Juveniles has oval body, compressed laterally, with an arched back and a flat belly; the mouth, very large, protractile and with fleshy lips, the skin is covered with ctenoid scales that make it rough to the touch; the branchial operculum has a pre-operculum; the caudal peduncle is long and well defined. As they mature, body color changes to white with increased brown spots and physical size transformation.
They swim with the head pointing down and with exaggerated fin movements to keep predators away. Like shown in the video below (video from Mikael Reuter)