A slim fish with a black stripe that widens toward the tail, dancing up and down over the same square meter of reef year after year. That dance is an advertisement, and the queue in front of it is the business.
Client fish arrive, hold still, spread their fins and open their mouths and gill covers, and the wrasse goes over them removing parasites and dead tissue - including inside the mouth of predators that would eat it in any other context. Reefs where cleaners were experimentally removed lost fish diversity within months: the service is load-bearing for the whole community.
It cheats, and the cheating is why the species is so studied. A cleaner prefers client mucus to parasites, and taking a bite of healthy mucus makes the client jolt and leave. So cleaners cheat less with clients that have somewhere else to go, more with captive ones, and behave better when other fish are watching them work - reputation management in a fish, tested experimentally many times over.
It also passed a mirror mark test in 2019: an individual with a mark placed where it can only be seen in a mirror tried to scrape it off. Whether that means self-recognition is argued about, loudly, and this animal is at the center of it.
The genus. Labroides Bleeker 1851 - -oides (having the form of Labrus). ETYFish
The species. Labroides dimidiatus (Valenciennes 1839) - halved or divided in two. ETYFish
- small slim fish, white in front shading to blue, with a black stripe widening to the tail
- swims with an exaggerated up-and-down dance to advertise
- always at the same spot, with a queue of larger fish waiting
- length up to 14 cm
Why it's threatened
There are no major threats known for this species, although it is targeted for the aquarium trade and there are occuring coral habitat degradation in parts of its range.
Threat classification from the IUCN Red List.
