Fish
Wrasse
Labridae · also called wrasses
Wrasses are the reef’s utility fish. The family runs from thumb-sized jewels to the two-metre humphead wrasse, and it includes the cleaner wrasse, a small fish that makes its living picking parasites off other fish — even out of the mouths of predators that could swallow it whole. Most wrasses also do something else unusual: they start life as females and some become males later.
Overview
Wrasses are the family Labridae, around 600 species, one of the largest families of marine fish, on reefs and rocky coasts worldwide and richest on Indo-Pacific reefs. They range from 5 cm dwarf wrasses to the humphead wrasse at over 2 m and 190 kg. Most eat hard-shelled invertebrates — snails, crabs, urchins — crushed with strong jaws and throat teeth. The parrotfish, once their own family, are now placed within the wrasses.
Female first
Most wrasses are protogynous hermaphrodites — they mature as females, and some change into males. When a harem’s dominant male dies, the largest female becomes male within days to weeks and takes over.
The cleaning station
The bluestreak cleaner wrasse runs a fixed station on the reef where other fish queue to have parasites and dead skin removed. Big predators tolerate it entering their mouths because the service is worth more than the snack — and removing cleaners from a reef measurably shrinks the other fish. In one study, a cleaner wrasse appeared to pass a mirror self-recognition test.
Reef gardeners
By eating sea urchins and, in the parrotfish, scraping algae and dead coral, wrasses help stop reefs turning to weed, so healthy wrasse populations are linked to reefs that recover better from bleaching.
Status
Wrasses as a family are Not Evaluated. Most small species are common, but large, slow-growing, sex-changing species are vulnerable — the humphead wrasse is Endangered and heavily targeted for the live reef food fish trade, and some parrotfish are depleted where they are speared faster than they mature.
Wrasse: common questions
How does a cleaner wrasse work, and why don't big fish eat it?
A bluestreak cleaner wrasse, and a few other cleaner species, sets up a fixed cleaning station on the reef, advertised by a bobbing dance and bold blue-and-black stripes. Other fish queue up and hold still, sometimes changing colour or opening their gills and mouths, while the wrasse picks off external parasites, dead skin, and mucus, which is its main food. Large predatory fish tolerate a small fish swimming into their mouths because the service is worth more than a snack, and a predator that ate its cleaner would find itself parasite-ridden and shunned. Cleaner wrasses also seem to recognise regular client fish and give them priority, and clients punish or avoid a wrasse that cheats by biting healthy tissue.
Do wrasses really change sex?
Yes, and it is the normal way of life for most of the family. Wrasses are typically protogynous, starting adult life as females and with the capacity to become male later. In many species a group is controlled by one large dominant male; when he dies or is removed, the largest female begins turning into a male within hours behaviourally and over one to two weeks physically, her ovaries remodelling into testes, and she takes over the group. Some wrasses also have males that are male from the start, which take a sneaking rather than a harem-holding approach. This flexible system lets a small population keep the right balance of sexes.
Are parrotfish a kind of wrasse?
Genetically, yes. Parrotfish were long treated as their own family, Scaridae, on the basis of their fused, beak-like teeth for scraping algae and coral, but molecular studies show they are nested well within the wrasses, and many biologists now classify them as a subfamily or tribe of Labridae. They share the wrasse traits of vivid colour, sex change, and a role as reef grazers, and several parrotfish sleep in the mucus cocoon described for some wrasses. So a parrotfish can reasonably be called a highly specialised, coral-scraping wrasse.
Which is the biggest wrasse?
The humphead wrasse, also called the Napoleon wrasse or Maori wrasse, is by far the largest, reaching over 2 metres and around 190 kilograms, with a prominent bulging forehead in large males and thick lips. It is a slow-growing, long-lived reef fish that can live 30 years or more and changes sex from female to male at around nine years old. Those same traits, together with its habit of gathering to spawn at predictable times and places, have made it easy to overfish, and it is now an Endangered species heavily sought for the live reef fish trade in parts of Asia, where a single large individual can fetch a very high price.