Short answers, pulled from the story.
Labridae is a family of marine ray-finned fish that contains over 600 species in 81 genera, divided into eight subfamilies. Many wrasses are brightly colored, and most are less than 20 cm long, though the humphead wrasse can reach up to 2.5 m.
In a 2019 study, bluestreak cleaner wrasses (Labroides dimidiatus) passed the mirror test, making them the first fish recorded to do so. The test's inventor, American psychologist Gordon G. Gallup, disputed the interpretation, suggesting the fish were likely trying to scrape off a perceived parasite rather than demonstrating self-recognition.
Most wrasses are protogynous hermaphrodites, meaning individuals are born functionally female and the largest can become male. Sex change is typically female-to-male, but placing two male Labroides dimidiatus in the same tank causes the smaller individual to revert to female.
Twenty-one species across eight wrasse genera have been documented smashing hard-shelled prey against rocks or coral used as anvils. At least some species remember and return to a specific anvil site. On one occasion, a blue tuskfish was filmed using an anvil on a young green sea turtle.
The word wrasse comes from the Cornish word wragh, a lenited form of gwragh meaning an old woman or hag, borrowed through the Cornish dialect form wrath. The same root appears in Welsh as gwrach and in Breton as gwrac'h.
Cleaner wrasses are deployed in commercial salmon farms to control sea-lice infestations. Scotland has developed a commercial fish-farming operation that produces cleaner wrasse specifically as pest-control agents, marketed as lice busters.