When I was taking the photo, I thought that they were just two cleaner wrasses (醫生魚) dancing around, but actually they are not. If you take a closer look, the fish on the top is a real Blue-streak cleaner wrasse (Labroides dimidiatus) whose mouth is at the tip of its head; while the fish below is a False cleanerfish (Aspidontus taeniatus) whose mouth is located slightly below the black stripe. The False cleanerfish mimics both the appearance and the behaviours of a cleaner wrasse, however, instead of “cleaning” the client fish, it attacks and tries to bite pieces of skin tissue from the client fish for food.
This is the first publish record of False cleanerfish (Aspidontus taeniatus) found in Hong Kong water.
*(Update on May 11, 2018) According to a study in 1983, False cleanerfish (Aspidontus taeniatus) mainly feed on fish eggs and tentacles of polychaete such as tubeworms; they rarely feed on the fins or skin tissue of the client fish.