Wrasse

• 1. Introduction

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  In 2019, a fish passed the mirror test. Not a dolphin, not a great ape, not an elephant. A small reef fish called the bluestreak cleaner wrasse, Labroides dimidiatus, looked at its own reflection and appeared to recognize itself. The finding rattled assumptions about animal consciousness that had stood for decades. But the cleaner wrasse is just one member of a sprawling family, Labridae, of more than 600 species spread across 81 genera. That family, the wrasses, turns out to be one of the most behaviorally complex, anatomically inventive, and ecologically varied groups of fish on the planet. How did a creature that fits in your palm end up at the center of debates about self-awareness, tool use, and the origins of sex itself?

• 2. A Name From Cornwall

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  The word wrasse reaches back to the Cornish language, where wragh is a lenited form of gwragh, meaning an old woman or hag. English speakers borrowed it through the Cornish dialect form wrath. The same root appears in Welsh as gwrach and in Breton as gwrac'h, tracing a line through the Celtic languages of the British Isles and Brittany. What exactly about the fish prompted that name is not recorded, but the family it describes ranges from the cold shores of Norway, where the Ballan wrasse survives in temperate waters, all the way through the tropical Atlantic, Indian, and Pacific Oceans. Most species stay close to the substrate, hugging coral reefs and rocky shores in shallow water where invertebrate prey is plentiful.

• 3. The Jaw as a Machine

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  Wrasses have become a primary study species in fish-feeding biomechanics, and the reason lies in a structure called the four-bar linkage. The nasal and mandibular bones connect at their rear ends to the rigid skull, and the maxilla joints tie the front tips of those two bones together, forming a closed loop of four rigid pieces linked by moving joints. That arrangement allows many different bone shapes to produce the same functional result, whether a fast jaw protrusion to snag a fleeing shrimp or a powerful crushing bite for a hard-shelled clam. The consequence shows up across wrasse lineages: different jaw forms converge on identical ecological outputs. Wrasse mouths are protractile, with separate teeth that jut outward, and many species have thick, sometimes peculiarly folded lips, a feature striking enough that German speakers called them Lippfische, lip-fish, and Dutch speakers coined lipvissen for the same reason.

• 4. Sex, Harems, and Nests

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  Most labrids are protogynous hermaphrodites, meaning individuals are born functionally female and the largest adults become territory-holding terminal-phase males. The California sheephead is a textbook example of this haremic mating system, where one dominant male controls a group of females. Wrasses actually exhibit three distinct mating systems: polygynous, lek-like, and promiscuous. Within those systems, spawning can happen as group events or as paired encounters, with the pattern depending on male body size. The default for the family is broadcast spawning, releasing large numbers of planktonic eggs to drift on tidal currents, with no parental involvement afterward. One subgroup breaks that pattern entirely. Fifteen of 23 species in the subfamily Labrinae, which split from the rest of the family during the Eocene, show broodcare: males of genera such as Symphodus, Centrolabrus, and Labrus build algae nests or hollow cavities, ventilate the eggs, and defend them against rival males and predators. In those species, eggs cannot survive without that care.

• 5. Evolutionary Pathways of Sex

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  Sex change in wrasses is typically female-to-male, but laboratory conditions have produced the reverse. Placing two male Labroides dimidiatus individuals in the same tank causes the smaller of the two to revert to female. Wrasses express three types of sexual development: functional gonochorism, where an individual is born one sex and stays that way; monandric protogyny, where all individuals start female but the largest can become male; and diandric protogyny, where individuals can be born either male or female, but females may still transition to male. Evolutionary analysis of wrasse lineages shows a trend toward monandry. Transitions directly from monandry to diandry are rare; lineages tend to pass through functional gonochorism as an intermediate step. Even the largest female in a group does not always change sex. Evidence shows she can, in some situations, maximize her own fitness by staying female and forgoing the transition.

• 6. Tool Use and the Anvil

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  Twenty-one species across eight wrasse genera have been documented smashing hard-shelled prey against large rocks or coral heads used as anvils. The list includes species of Choerodon, Coris, Cheilinus, Thalassoma, Symphodus, Halichoeres, Bodianus, and Pseudolabrus. Prey items are typically clams, sea urchins, and crabs. At least some of these species return to the same anvil repeatedly, suggesting they can remember and locate a specific tool site. On one documented occasion, a blue tuskfish was filmed using an anvil not on an invertebrate but on a young green sea turtle. The behavior places wrasses in a short list of non-primate animals that use objects as tools, and the consistency of anvil reuse raises questions about the cognitive map a small reef fish carries of its own territory.

• 7. Cleaners, Cheaters, and the Mirror

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  Cleaner wrasses run what are effectively service stations on tropical reefs. Larger fish, including predatory species, queue at these cleaning stations and wait while Labroides dimidiatus individuals remove gnathiid parasites, sometimes swimming into open mouths and gill cavities to do so. Predators rarely eat the cleaners, which may reflect the value of having a reliable cleaning partner. Cleaner wrasses also cheat. They are known to consume healthy mucus and tissue from their clients, which costs the client metabolically. The 2019 mirror test study found that bluestreak cleaner wrasses passed the test, the first fish recorded to do so. The test's inventor, American psychologist Gordon G. Gallup, disputed the interpretation, arguing the fish were likely attempting to scrape off a perceived parasite rather than demonstrating self-recognition. The study's authors responded that the fish inspected themselves in the mirror both before and after scraping, which they argued indicated genuine self-awareness. A 2024 study complicated the picture further: mirror-naive bluestreak cleaner wrasses initially showed aggression toward photographs of wrasses sized 10% larger or 10% smaller than themselves, but after seeing their own reflections, they stopped confronting the larger images.

• 8. Wrasses and Humans

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  Tautog, a wrasse species native to the Western Atlantic coast of North America, was the most common food fish for indigenous people in that region. Today wrasses appear widely in public and private aquaria, and several smaller species are considered reef safe, coexisting with coral without damaging it. A more recent application has emerged in commercial salmon farming: cleaner wrasses are deployed to control sea-lice infestations, and Scotland has developed a commercial fish-farming operation specifically to produce cleaner wrasse as pest-control agents, marketing them as lice busters. The 2015 study by Munoz and Diaz catalogued 338 parasite taxa taken from 127 labrid species, a figure that underlines how embedded wrasses are in marine food webs. The fossil record stretches back to the Early Eocene at Monte Bolca, Italy, and wrasse remains from the Middle Eocene La Meseta Formation in Antarctica show that the family once ranged far wider than it does today, before the continent's cooling during the Oligocene erased them from the southern pole.