This is a small wrasse, averaging 10 cm long. It can be recognized thanks to a wide longitudinal black stripe running along the side and eye; the back and the stomach are white. This white part changes to a bright blue on the front of the animal, while the black band widens at the tail. The young are black with an electric blue line. A genetic analysis of L. dimidiatus revealed the population fell into two monophyleticclades, with Indian Ocean populations generally having different stripe widths to western Pacific fishes. The Japanese cleaner wrasses, though, fell within the same group as Indian Ocean fish, despite differing in appearance, and both clades overlap around Papua New Guinea. Two closely related cleaner wrasse species, Labroides pectoralis and Labroides bicolor, were grouped inside the L. dimidiatus clade, so the bluestreak cleaner wrasse may in fact be polyphyletic, incorporating several species.
Distribution
The bluestreak cleaner wrasse is found on coral reefs in the tropics from the Red Sea and Indian Ocean to the western Pacific. It was first recorded from the Kermadec Islands Marine Reserve north of New Zealand in 2015, after researchers examined hundreds of hours of unused documentary film footage.
Cleaning
Cleaner wrasses are usually found at cleaning stations. Cleaning stations are occupied by different units of cleaner wrasses, such as a group of youths, a pair of adults, or a group of females accompanied by a dominant male. When visitors come near the cleaning stations, the cleaner wrasses greet the visitors by performing a dance-like motion in which they move their rear up and down. The visitors are referred to as "clients". Bluestreak cleaner wrasses clean to consume ectoparasites on client fish for food. The bigger fish recognise them as cleaner fish because they have a lateral stripe along the length of their bodies, and by their movement patterns. Cleaner wrasses greet visitors in an effort to secure the food source and cleaning opportunity with the client. Upon recognising the cleaner and successfully soliciting its attention, the client fish adopts a species-specific pose to allow the cleaner access to its body surface, gills and sometimes mouth. Other fish that engage in such cleaning behavior include goby fish . Some fish mimic cleaner wrasses. For example, a species of blenny called Aspidontus taeniatus has evolved the same behavior to tear small pieces of flesh or skin from bigger fish rather than rid them of parasites. Another species, the bluestreak fangblenny, Plagiotremus rhinorhynchos'', mimics juvenile cleaner wrasse so its presence is tolerated by the cleaners, which, it is assumed, enables it to take advantage of the concentration of potential victims.
