s working on gill area of dragon wrasse
Novaculichthys taeniourus, on a reef in
Hawaii|thumb|right|alt=Photo of two small wrasses cleaning large wrasse's gills Cleaner wrasses are the best-known of the
cleaner fish. They live in a
cleaning symbiosis with larger, often predatory, fish, grooming them and benefiting by consuming what they remove. "Client" fish congregate at wrasse "
cleaning stations" and wait for the cleaner fish to remove
gnathiid parasites, the cleaners even swimming into their open mouths and gill cavities to do so. Cleaner wrasses are best known for feeding on dead tissue, scales, and
ectoparasites, although they are also known to '
cheat', consuming healthy tissue and mucus, which is energetically costly for the client fish to produce. The
bluestreak cleaner wrasse,
Labroides dimidiatus, is one of the most common cleaners found on tropical reefs. Few cleaner wrasses have been observed being eaten by predators, possibly because predator survival is more important than the parasite removal. In a 2019 study, cleaner wrasses passed the
mirror test, the first fish to do so. However, the test's inventor, American psychologist
Gordon G. Gallup, has said that the fish were most likely trying to scrape off a perceived parasite on another fish and that they did not demonstrate self-recognition. The authors of the study retorted that because the fish checked themselves in the mirror before and after the scraping, this meant that the fish had self-awareness and recognized that their reflections belonged to their own bodies. In a 2024 study, "mirror-naive" bluestreak cleaner wrasse were reported to initially show aggression to wrasse photographs sized 10% larger or 10% smaller than themselves, regardless of size. However, upon viewing their reflections in a mirror, they avoided confronting photographs 10% larger than they were. ==Significance to humans==